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• Big Data – Buzz Words: What is Hadoop – Day 6 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned what is NoSQL. In this article we will take a quick look at one of the four most important buzz words which goes around Big Data – Hadoop. What is Hadoop? Apache Hadoop is an open-source, free and Java based software framework offers a powerful distributed platform to store and manage Big Data. It is licensed under an Apache V2 license. It runs applications on large clusters of commodity hardware and it processes thousands of terabytes of data on thousands of the nodes. Hadoop is inspired from Google’s MapReduce and Google File System (GFS) papers. The major advantage of Hadoop framework is that it provides reliability and high availability. What are the core components of Hadoop? There are two major components of the Hadoop framework and both fo them does two of the important task for it. Hadoop MapReduce is the method to split a larger data problem into smaller chunk and distribute it to many different commodity servers. Each server have their own set of resources and they have processed them locally. Once the commodity server has processed the data they send it back collectively to main server. This is effectively a process where we process large data effectively and efficiently. (We will understand this in tomorrow’s blog post). Hadoop Distributed File System (HDFS) is a virtual file system. There is a big difference between any other file system and Hadoop. When we move a file on HDFS, it is automatically split into many small pieces. These small chunks of the file are replicated and stored on other servers (usually 3) for the fault tolerance or high availability. (We will understand this in the day after tomorrow’s blog post). Besides above two core components Hadoop project also contains following modules as well. Hadoop Common: Common utilities for the other Hadoop modules Hadoop Yarn: A framework for job scheduling and cluster resource management There are a few other projects (like Pig, Hive) related to above Hadoop as well which we will gradually explore in later blog posts. A Multi-node Hadoop Cluster Architecture Now let us quickly see the architecture of the a multi-node Hadoop cluster. A small Hadoop cluster includes a single master node and multiple worker or slave node. As discussed earlier, the entire cluster contains two layers. One of the layer of MapReduce Layer and another is of HDFC Layer. Each of these layer have its own relevant component. The master node consists of a JobTracker, TaskTracker, NameNode and DataNode. A slave or worker node consists of a DataNode and TaskTracker. It is also possible that slave node or worker node is only data or compute node. The matter of the fact that is the key feature of the Hadoop. In this introductory blog post we will stop here while describing the architecture of Hadoop. In a future blog post of this 31 day series we will explore various components of Hadoop Architecture in Detail. Why Use Hadoop? There are many advantages of using Hadoop. Let me quickly list them over here: Robust and Scalable – We can add new nodes as needed as well modify them. Affordable and Cost Effective – We do not need any special hardware for running Hadoop. We can just use commodity server. Adaptive and Flexible – Hadoop is built keeping in mind that it will handle structured and unstructured data. Highly Available and Fault Tolerant – When a node fails, the Hadoop framework automatically fails over to another node. Why Hadoop is named as Hadoop? In year 2005 Hadoop was created by Doug Cutting and Mike Cafarella while working at Yahoo. Doug Cutting named Hadoop after his son’s toy elephant. Tomorrow In tomorrow’s blog post we will discuss Buzz Word – MapReduce. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• Using Hadooop (HDInsight) with Microsoft - Two (OK, Three) Options

  - by BuckWoody

  Microsoft has many tools for “Big Data”. In fact, you need many tools – there’s no product called “Big Data Solution” in a shrink-wrapped box – if you find one, you probably shouldn’t buy it. It’s tempting to want a single tool that handles everything in a problem domain, but with large, complex data, that isn’t a reality. You’ll mix and match several systems, open and closed source, to solve a given problem. But there are tools that help with handling data at large, complex scales. Normally the best way to do this is to break up the data into parts, and then put the calculation engines for that chunk of data right on the node where the data is stored. These systems are in a family called “Distributed File and Compute”. Microsoft has a couple of these, including the High Performance Computing edition of Windows Server. Recently we partnered with Hortonworks to bring the Apache Foundation’s release of Hadoop to Windows. And as it turns out, there are actually two (technically three) ways you can use it. (There’s a more detailed set of information here: http://www.microsoft.com/sqlserver/en/us/solutions-technologies/business-intelligence/big-data.aspx, I’ll cover the options at a general level below)  First Option: Windows Azure HDInsight Service  Your first option is that you can simply log on to a Hadoop control node and begin to run Pig or Hive statements against data that you have stored in Windows Azure. There’s nothing to set up (although you can configure things where needed), and you can send the commands, get the output of the job(s), and stop using the service when you are done – and repeat the process later if you wish. (There are also connectors to run jobs from Microsoft Excel, but that’s another post)   This option is useful when you have a periodic burst of work for a Hadoop workload, or the data collection has been happening into Windows Azure storage anyway. That might be from a web application, the logs from a web application, telemetrics (remote sensor input), and other modes of constant collection.   You can read more about this option here:  http://blogs.msdn.com/b/windowsazure/archive/2012/10/24/getting-started-with-windows-azure-hdinsight-service.aspx Second Option: Microsoft HDInsight Server Your second option is to use the Hadoop Distribution for on-premises Windows called Microsoft HDInsight Server. You set up the Name Node(s), Job Tracker(s), and Data Node(s), among other components, and you have control over the entire ecostructure.   This option is useful if you want to  have complete control over the system, leave it running all the time, or you have a huge quantity of data that you have to bulk-load constantly – something that isn’t going to be practical with a network transfer or disk-mailing scheme. You can read more about this option here: http://www.microsoft.com/sqlserver/en/us/solutions-technologies/business-intelligence/big-data.aspx Third Option (unsupported): Installation on Windows Azure Virtual Machines  Although unsupported, you could simply use a Windows Azure Virtual Machine (we support both Windows and Linux servers) and install Hadoop yourself – it’s open-source, so there’s nothing preventing you from doing that.   Aside from being unsupported, there are other issues you’ll run into with this approach – primarily involving performance and the amount of configuration you’ll need to do to access the data nodes properly. But for a single-node installation (where all components run on one system) such as learning, demos, training and the like, this isn’t a bad option. Did I mention that’s unsupported? :) You can learn more about Windows Azure Virtual Machines here: http://www.windowsazure.com/en-us/home/scenarios/virtual-machines/ And more about Hadoop and the installation/configuration (on Linux) here: http://en.wikipedia.org/wiki/Apache_Hadoop And more about the HDInsight installation here: http://www.microsoft.com/web/gallery/install.aspx?appid=HDINSIGHT-PREVIEW Choosing the right option Since you have two or three routes you can go, the best thing to do is evaluate the need you have, and place the workload where it makes the most sense.  My suggestion is to install the HDInsight Server locally on a test system, and play around with it. Read up on the best ways to use Hadoop for a given workload, understand the parts, write a little Pig and Hive, and get your feet wet. Then sign up for a test account on HDInsight Service, and see how that leverages what you know. If you're a true tinkerer, go ahead and try the VM route as well. Oh - there’s another great reference on the Windows Azure HDInsight that just came out, here: http://blogs.msdn.com/b/brunoterkaly/archive/2012/11/16/hadoop-on-azure-introduction.aspx  

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• Big Data – Buzz Words: What is HDFS – Day 8 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned what is MapReduce. In this article we will take a quick look at one of the four most important buzz words which goes around Big Data – HDFS. What is HDFS ? HDFS stands for Hadoop Distributed File System and it is a primary storage system used by Hadoop. It provides high performance access to data across Hadoop clusters. It is usually deployed on low-cost commodity hardware. In commodity hardware deployment server failures are very common. Due to the same reason HDFS is built to have high fault tolerance. The data transfer rate between compute nodes in HDFS is very high, which leads to reduced risk of failure. HDFS creates smaller pieces of the big data and distributes it on different nodes. It also copies each smaller piece to multiple times on different nodes. Hence when any node with the data crashes the system is automatically able to use the data from a different node and continue the process. This is the key feature of the HDFS system. Architecture of HDFS The architecture of the HDFS is master/slave architecture. An HDFS cluster always consists of single NameNode. This single NameNode is a master server and it manages the file system as well regulates access to various files. In additional to NameNode there are multiple DataNodes. There is always one DataNode for each data server. In HDFS a big file is split into one or more blocks and those blocks are stored in a set of DataNodes. The primary task of the NameNode is to open, close or rename files and directory and regulate access to the file system, whereas the primary task of the DataNode is read and write to the file systems. DataNode is also responsible for the creation, deletion or replication of the data based on the instruction from NameNode. In reality, NameNode and DataNode are software designed to run on commodity machine build in Java language. Visual Representation of HDFS Architecture Let us understand how HDFS works with the help of the diagram. Client APP or HDFS Client connects to NameSpace as well as DataNode. Client App access to the DataNode is regulated by NameSpace Node. NameSpace Node allows Client App to connect to the DataNode based by allowing the connection to the DataNode directly. A big data file is divided into multiple data blocks (let us assume that those data chunks are A,B,C and D. Client App will later on write data blocks directly to the DataNode. Client App does not have to directly write to all the node. It just has to write to any one of the node and NameNode will decide on which other DataNode it will have to replicate the data. In our example Client App directly writes to DataNode 1 and detained 3. However, data chunks are automatically replicated to other nodes. All the information like in which DataNode which data block is placed is written back to NameNode. High Availability During Disaster Now as multiple DataNode have same data blocks in the case of any DataNode which faces the disaster, the entire process will continue as other DataNode will assume the role to serve the specific data block which was on the failed node. This system provides very high tolerance to disaster and provides high availability. If you notice there is only single NameNode in our architecture. If that node fails our entire Hadoop Application will stop performing as it is a single node where we store all the metadata. As this node is very critical, it is usually replicated on another clustered as well as on another data rack. Though, that replicated node is not operational in architecture, it has all the necessary data to perform the task of the NameNode in the case of the NameNode fails. The entire Hadoop architecture is built to function smoothly even there are node failures or hardware malfunction. It is built on the simple concept that data is so big it is impossible to have come up with a single piece of the hardware which can manage it properly. We need lots of commodity (cheap) hardware to manage our big data and hardware failure is part of the commodity servers. To reduce the impact of hardware failure Hadoop architecture is built to overcome the limitation of the non-functioning hardware. Tomorrow In tomorrow’s blog post we will discuss the importance of the relational database in Big Data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• Computer Networks UNISA - Chap 14 &ndash; Insuring Integrity &amp; Availability

  - by MarkPearl

  After reading this section you should be able to Identify the characteristics of a network that keep data safe from loss or damage Protect an enterprise-wide network from viruses Explain network and system level fault tolerance techniques Discuss issues related to network backup and recovery strategies Describe the components of a useful disaster recovery plan and the options for disaster contingencies What are integrity and availability? Integrity – the soundness of a networks programs, data, services, devices, and connections Availability – How consistently and reliably a file or system can be accessed by authorized personnel A number of phenomena can compromise both integrity and availability including… security breaches natural disasters malicious intruders power flaws human error users etc Although you cannot predict every type of vulnerability, you can take measures to guard against the most damaging events. The following are some guidelines… Allow only network administrators to create or modify NOS and application system users. Monitor the network for unauthorized access or changes Record authorized system changes in a change management system’ Install redundant components Perform regular health checks on the network Check system performance, error logs, and the system log book regularly Keep backups Implement and enforce security and disaster recovery policies These are just some of the basics… Malware Malware refers to any program or piece of code designed to intrude upon or harm a system or its resources. Types of Malware… Boot sector viruses Macro viruses File infector viruses Worms Trojan Horse Network Viruses Bots Malware characteristics Some common characteristics of Malware include… Encryption Stealth Polymorphism Time dependence Malware Protection There are various tools available to protect you from malware called anti-malware software. These monitor your system for indications that a program is performing potential malware operations. A number of techniques are used to detect malware including… Signature Scanning Integrity Checking Monitoring unexpected file changes or virus like behaviours It is important to decide where anti-malware tools will be installed and find a balance between performance and protection. There are several general purpose malware policies that can be implemented to protect your network including… Every compute in an organization should be equipped with malware detection and cleaning software that regularly runs Users should not be allowed to alter or disable the anti-malware software Users should know what to do in case the anti-malware program detects a malware virus Users should be prohibited from installing any unauthorized software on their systems System wide alerts should be issued to network users notifying them if a serious malware virus has been detected. Fault Tolerance Besides guarding against malware, another key factor in maintaining the availability and integrity of data is fault tolerance. Fault tolerance is the ability for a system to continue performing despite an unexpected hardware or software malfunction. Fault tolerance can be realized in varying degrees, the optimal level of fault tolerance for a system depends on how critical its services and files are to productivity. Generally the more fault tolerant the system, the more expensive it is. The following describe some of the areas that need to be considered for fault tolerance. Environment (Temperature and humidity) Power Topology and Connectivity Servers Storage Power Typical power flaws include Surges – a brief increase in voltage due to lightening strikes, solar flares or some idiot at City Power Noise – Fluctuation in voltage levels caused by other devices on the network or electromagnetic interference Brownout – A sag in voltage for just a moment Blackout – A complete power loss The are various alternate power sources to consider including UPS’s and Generators. UPS’s are found in two categories… Standby UPS – provides continuous power when mains goes down (brief period of switching over) Online UPS – is online all the time and the device receives power from the UPS all the time (the UPS is charged continuously) Servers There are various techniques for fault tolerance with servers. Server mirroring is an option where one device or component duplicates the activities of another. It is generally an expensive process. Clustering is a fault tolerance technique that links multiple servers together to appear as a single server. They share processing and storage responsibilities and if one unit in the cluster goes down, another unit can be brought in to replace it. Storage There are various techniques available including the following… RAID Arrays NAS (Storage (Network Attached Storage) SANs (Storage Area Networks) Data Backup A backup is a copy of data or program files created for archiving or safekeeping. Many different options for backups exist with various media including… These vary in cost and speed. Optical Media Tape Backup External Disk Drives Network Backups Backup Strategy After selecting the appropriate tool for performing your servers backup, devise a backup strategy to guide you through performing reliable backups that provide maximum data protection. Questions that should be answered include… What data must be backed up At what time of day or night will the backups occur How will you verify the accuracy of the backups Where and for how long will backup media be stored Who will take responsibility for ensuring that backups occurred How long will you save backups Where will backup and recovery documentation be stored Different backup methods provide varying levels of certainty and corresponding labour cost. There are also different ways to determine which files should be backed up including… Full backup – all data on all servers is copied to storage media Incremental backup – Only data that has changed since the last full or incremental backup is copied to a storage medium Differential backup – Only data that has changed since the last backup is coped to a storage medium Disaster Recovery Disaster recovery is the process of restoring your critical functionality and data after an enterprise wide outage has occurred. A disaster recovery plan is for extreme scenarios (i.e. fire, line fault, etc). A cold site is a place were the computers, devices, and connectivity necessary to rebuild a network exist but they are not appropriately configured. A warm site is a place where the computers, devices, and connectivity necessary to rebuild a network exists with some appropriately configured devices. A hot site is a place where the computers, devices, and connectivity necessary to rebuild a network exists and all are appropriately configured.

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• Trying to detect collision between two polygons using Separating Axis Theorem

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Cocos2d: Moving background on update: offsett issue

  - by mm24

  working with Objective C, iOS and Cocos2d I am developing a vertical scrolling shooter game for iPhone (retina display models with 640 width x 960 height pixel resolution). My basic algorithm works as following: I create two instances of an image that has exactly 640 width x 960 height pixel of resolution, which we will call imageA and imageB I then set the two imags with exactly 480.0f of offset from each other, as the screenSize of a CCScene is set by default to 480.0f. At each update method call I move the two images by the same value. I make sure that their offsett stays to 480.0f However when running the game I see a 1 pixel height line between the two images. This literally bugs me and would like to adjust this. What am I doing wrong? This is a zoom in on the background when the "offsett line" is visible. The white line you can see divides the two background images and is not meant to exist as both images are completely black :): If I change the yPositionOfSecondElement value to 479.0f until the first loop the two images overlap correctly, but as soon as the loop starts the two images starts having an offsett of -1.0f. Here is the initialization code: -(void) init { //... screenHeight = 480.0f; yPositionOfSecondElement= screenHeight;//I tried subtracting an offsett of -1 but eventually the image would go wrong again yPositionOfFirstElement = 0.0f; loopedBackgroundImageInstanceA = [BackgroundLoopedImage loopImageForLevel:levelName]; loopedBackgroundImageInstanceA.anchorPoint = CGPointMake(0.5f, 0.0f); loopedBackgroundImageInstanceA.position = CGPointMake(160.0f, yPositionOfFirstElement); [node addChild:loopedBackgroundImageInstanceA z:zLevelBackground]; //loopedBackgroundImageInstanceA.color= ccRED; loopedBackgroundImageInstanceB = [BackgroundLoopedImage loopImageForLevel:levelName]; loopedBackgroundImageInstanceB.anchorPoint = CGPointMake(0.5f, 0.0f); loopedBackgroundImageInstanceB.position = CGPointMake(160.0f, yPositionOfSecondElement); [node addChild:loopedBackgroundImageInstanceB z:zLevelBackground]; //.... } And here is the move code called at each update: -(void) moveBackgroundSprites:(BackgroundLoopedImage*)imageA :(BackgroundLoopedImage*)imageB :(ccTime)delta { isEligibleToMove=false; //This is done to avoid rounding errors float yStep = delta * [GameController sharedGameController].currentBackgroundSpeed; NSString* formattedNumber = [NSString stringWithFormat:@"%.02f", yStep]; yStep = atof([formattedNumber UTF8String]); //First should adjust position of images [self adjustPosition:imageA :imageB]; //The can get the actual image position CGPoint posA = imageA.position; CGPoint posB = imageB.position; //Here could verify if the checksum is equal to the required difference (should be 479.0f) if (![self verifyCheckSum:posA :posB]) { CCLOG(@"does not comply A"); } //At this stage can compute the hypotetical new position CGPoint newPosA = CGPointMake(posA.x, posA.y - yStep); CGPoint newPosB = CGPointMake(posB.x, posB.y - yStep); // Reposition stripes when they're out of bounds if (newPosA.y <= -yPositionOfSecondElement) { newPosA.y = yPositionOfSecondElement; [imageA shuffle]; if (timeElapsed>=endTime && hasReachedEndLevel==FALSE) { hasReachedEndLevel=TRUE; shouldMoveImageEnd=TRUE; } } else if (newPosB.y <= -yPositionOfSecondElement) { newPosB.y = yPositionOfSecondElement; [imageB shuffle]; if (timeElapsed>=endTime && hasReachedEndLevel==FALSE) { hasReachedEndLevel=TRUE; shouldMoveImageEnd=TRUE; } } //Here should verify that the check sum is equal to 479.0f if (![self verifyCheckSum:posA :posB]) { CCLOG(@"does not comply B"); } imageA.position = newPosA; imageB.position = newPosB; //Here could verify that the check sum is equal to 479.0f if (![self verifyCheckSum:posA :posB]) { CCLOG(@"does not comply C"); } isEligibleToMove=true; } -(BOOL) verifyCheckSum:(CGPoint)posA :(CGPoint)posB { BOOL comply = false; float sum = 0.0f; if (posA.y > posB.y) { sum = posA.y - posB.y; } else if (posB.y > posA.y){ sum = posB.y - posA.y; } else{ return false; } if (sum!=yPositionOfSecondElement) { comply= false; } else{ comply=true; } return comply; } And here is what happens on the update: if(shouldMoveImageA && shouldMoveImageB) { if (isEligibleToMove) { [self moveBackgroundSprites:loopedBackgroundImageInstanceA :loopedBackgroundImageInstanceB :delta]; } Forget about shouldMoveImageA and shouldMoveImageB, this is just for when the background reaches the end of level, this works.

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• Quadratic Programming with Oracle R Enterprise

  - by Jeff Taylor-Oracle

       I wanted to use quadprog with ORE on a server running Oracle Solaris 11.2 on a Oracle SPARC T-4 server For background, see: Oracle SPARC T4-2 http://docs.oracle.com/cd/E23075_01/ Oracle Solaris 11.2 http://www.oracle.com/technetwork/server-storage/solaris11/overview/index.html quadprog: Functions to solve Quadratic Programming Problems http://cran.r-project.org/web/packages/quadprog/index.html Oracle R Enterprise 1.4 ("ORE") 1.4 http://www.oracle.com/technetwork/database/options/advanced-analytics/r-enterprise/ore-downloads-1502823.html Problem: path to Solaris Studio doesn't match my installation: $ ORE CMD INSTALL quadprog_1.5-5.tar.gz * installing to library \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library\u2019 * installing *source* package \u2018quadprog\u2019 ... ** package \u2018quadprog\u2019 successfully unpacked and MD5 sums checked ** libs /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c aind.f -o aind.o bash: /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95: No such file or directory *** Error code 1 make: Fatal error: Command failed for target `aind.o' ERROR: compilation failed for package \u2018quadprog\u2019 * removing \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library/quadprog\u2019 $ ls -l /opt/solarisstudio12.3/bin/f95 lrwxrwxrwx   1 root     root          15 Aug 19 17:36 /opt/solarisstudio12.3/bin/f95 -> ../prod/bin/f90 Solution: a symbolic link: $ sudo mkdir -p /opt/SunProd/studio12u3 $ sudo ln -s /opt/solarisstudio12.3 /opt/SunProd/studio12u3/ Now, it is all good: $ ORE CMD INSTALL quadprog_1.5-5.tar.gz * installing to library \u2018/u01/app/oracle/product/12.1.0/dbhome_1/R/library\u2019 * installing *source* package \u2018quadprog\u2019 ... ** package \u2018quadprog\u2019 successfully unpacked and MD5 sums checked ** libs /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c aind.f -o aind.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/ cc -xc99 -m64 -I/usr/lib/64/R/include -DNDEBUG -KPIC  -xlibmieee  -c init.c -o init.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64  -PIC -g  -c -o solve.QP.compact.o solve.QP.compact.f /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64  -PIC -g  -c -o solve.QP.o solve.QP.f /opt/SunProd/studio12u3/solarisstudio12.3/bin/f95 -m64   -PIC  -g  -c util.f -o util.o /opt/SunProd/studio12u3/solarisstudio12.3/bin/ cc -xc99 -m64 -G -o quadprog.so aind.o init.o solve.QP.compact.o solve.QP.o util.o -xlic_lib=sunperf -lsunmath -lifai -lsunimath -lfai -lfai2 -lfsumai -lfprodai -lfminlai -lfmaxlai -lfminvai -lfmaxvai -lfui -lfsu -lsunmath -lmtsk -lm -lifai -lsunimath -lfai -lfai2 -lfsumai -lfprodai -lfminlai -lfmaxlai -lfminvai -lfmaxvai -lfui -lfsu -lsunmath -lmtsk -lm -L/usr/lib/64/R/lib -lR installing to /u01/app/oracle/product/12.1.0/dbhome_1/R/library/quadprog/libs ** R ** preparing package for lazy loading ** help *** installing help indices   converting help for package \u2018quadprog\u2019     finding HTML links ... done     solve.QP                                html      solve.QP.compact                        html  ** building package indices ** testing if installed package can be loaded * DONE (quadprog) ====== Here is an example from http://cran.r-project.org/web/packages/quadprog/quadprog.pdf > require(quadprog) > Dmat <- matrix(0,3,3) > diag(Dmat) <- 1 > dvec <- c(0,5,0) > Amat <- matrix(c(-4,-3,0,2,1,0,0,-2,1),3,3) > bvec <- c(-8,2,0) > solve.QP(Dmat,dvec,Amat,bvec=bvec) $solution [1] 0.4761905 1.0476190 2.0952381 $value [1] -2.380952 $unconstrained.solution [1] 0 5 0 $iterations [1] 3 0 $Lagrangian [1] 0.0000000 0.2380952 2.0952381 $iact [1] 3 2 Here, the standard example is modified to work with Oracle R Enterprise require(ORE) ore.connect("my-name", "my-sid", "my-host", "my-pass", 1521) ore.doEval(   function () {     require(quadprog)   } ) ore.doEval(   function () {     Dmat <- matrix(0,3,3)     diag(Dmat) <- 1     dvec <- c(0,5,0)     Amat <- matrix(c(-4,-3,0,2,1,0,0,-2,1),3,3)     bvec <- c(-8,2,0)    solve.QP(Dmat,dvec,Amat,bvec=bvec)   } ) $solution [1] 0.4761905 1.0476190 2.0952381 $value [1] -2.380952 $unconstrained.solution [1] 0 5 0 $iterations [1] 3 0 $Lagrangian [1] 0.0000000 0.2380952 2.0952381 $iact [1] 3 2 Now I can combine the quadprog compute algorithms with the Oracle R Enterprise Database engine functionality: Scale to large datasets Access to tables, views, and external tables in the database, as well as those accessible through database links Use SQL query parallel execution Use in-database statistical and data mining functionality

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• How can I estimate the entropy of a password?

  - by Wug

  Having read various resources about password strength I'm trying to create an algorithm that will provide a rough estimation of how much entropy a password has. I'm trying to create an algorithm that's as comprehensive as possible. At this point I only have pseudocode, but the algorithm covers the following: password length repeated characters patterns (logical) different character spaces (LC, UC, Numeric, Special, Extended) dictionary attacks It does NOT cover the following, and SHOULD cover it WELL (though not perfectly): ordering (passwords can be strictly ordered by output of this algorithm) patterns (spatial) Can anyone provide some insight on what this algorithm might be weak to? Specifically, can anyone think of situations where feeding a password to the algorithm would OVERESTIMATE its strength? Underestimations are less of an issue. The algorithm: // the password to test password = ? length = length(password) // unique character counts from password (duplicates discarded) uqlca = number of unique lowercase alphabetic characters in password uquca = number of uppercase alphabetic characters uqd = number of unique digits uqsp = number of unique special characters (anything with a key on the keyboard) uqxc = number of unique special special characters (alt codes, extended-ascii stuff) // algorithm parameters, total sizes of alphabet spaces Nlca = total possible number of lowercase letters (26) Nuca = total uppercase letters (26) Nd = total digits (10) Nsp = total special characters (32 or something) Nxc = total extended ascii characters that dont fit into other categorys (idk, 50?) // algorithm parameters, pw strength growth rates as percentages (per character) flca = entropy growth factor for lowercase letters (.25 is probably a good value) fuca = EGF for uppercase letters (.4 is probably good) fd = EGF for digits (.4 is probably good) fsp = EGF for special chars (.5 is probably good) fxc = EGF for extended ascii chars (.75 is probably good) // repetition factors. few unique letters == low factor, many unique == high rflca = (1 - (1 - flca) ^ uqlca) rfuca = (1 - (1 - fuca) ^ uquca) rfd = (1 - (1 - fd ) ^ uqd ) rfsp = (1 - (1 - fsp ) ^ uqsp ) rfxc = (1 - (1 - fxc ) ^ uqxc ) // digit strengths strength = ( rflca * Nlca + rfuca * Nuca + rfd * Nd + rfsp * Nsp + rfxc * Nxc ) ^ length entropybits = log_base_2(strength) A few inputs and their desired and actual entropy_bits outputs: INPUT DESIRED ACTUAL aaa very pathetic 8.1 aaaaaaaaa pathetic 24.7 abcdefghi weak 31.2 H0ley$Mol3y_ strong 72.2 s^fU¬5ü;y34G< wtf 88.9 [a^36]* pathetic 97.2 [a^20]A[a^15]* strong 146.8 xkcd1** medium 79.3 xkcd2** wtf 160.5 * these 2 passwords use shortened notation, where [a^N] expands to N a's. ** xkcd1 = "Tr0ub4dor&3", xkcd2 = "correct horse battery staple" The algorithm does realize (correctly) that increasing the alphabet size (even by one digit) vastly strengthens long passwords, as shown by the difference in entropy_bits for the 6th and 7th passwords, which both consist of 36 a's, but the second's 21st a is capitalized. However, they do not account for the fact that having a password of 36 a's is not a good idea, it's easily broken with a weak password cracker (and anyone who watches you type it will see it) and the algorithm doesn't reflect that. It does, however, reflect the fact that xkcd1 is a weak password compared to xkcd2, despite having greater complexity density (is this even a thing?). How can I improve this algorithm? Addendum 1 Dictionary attacks and pattern based attacks seem to be the big thing, so I'll take a stab at addressing those. I could perform a comprehensive search through the password for words from a word list and replace words with tokens unique to the words they represent. Word-tokens would then be treated as characters and have their own weight system, and would add their own weights to the password. I'd need a few new algorithm parameters (I'll call them lw, Nw ~= 2^11, fw ~= .5, and rfw) and I'd factor the weight into the password as I would any of the other weights. This word search could be specially modified to match both lowercase and uppercase letters as well as common character substitutions, like that of E with 3. If I didn't add extra weight to such matched words, the algorithm would underestimate their strength by a bit or two per word, which is OK. Otherwise, a general rule would be, for each non-perfect character match, give the word a bonus bit. I could then perform simple pattern checks, such as searches for runs of repeated characters and derivative tests (take the difference between each character), which would identify patterns such as 'aaaaa' and '12345', and replace each detected pattern with a pattern token, unique to the pattern and length. The algorithmic parameters (specifically, entropy per pattern) could be generated on the fly based on the pattern. At this point, I'd take the length of the password. Each word token and pattern token would count as one character; each token would replace the characters they symbolically represented. I made up some sort of pattern notation, but it includes the pattern length l, the pattern order o, and the base element b. This information could be used to compute some arbitrary weight for each pattern. I'd do something better in actual code. Modified Example: Password: 1234kitty$$$$$herpderp Tokenized: 1 2 3 4 k i t t y $ $ $ $ $ h e r p d e r p Words Filtered: 1 2 3 4 @W5783 $ $ $ $ $ @W9001 @W9002 Patterns Filtered: @P[l=4,o=1,b='1'] @W5783 @P[l=5,o=0,b='$'] @W9001 @W9002 Breakdown: 3 small, unique words and 2 patterns Entropy: about 45 bits, as per modified algorithm Password: correcthorsebatterystaple Tokenized: c o r r e c t h o r s e b a t t e r y s t a p l e Words Filtered: @W6783 @W7923 @W1535 @W2285 Breakdown: 4 small, unique words and no patterns Entropy: 43 bits, as per modified algorithm The exact semantics of how entropy is calculated from patterns is up for discussion. I was thinking something like: entropy(b) * l * (o + 1) // o will be either zero or one The modified algorithm would find flaws with and reduce the strength of each password in the original table, with the exception of s^fU¬5ü;y34G<, which contains no words or patterns.

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• Macports irssi & perl5 installation issues

  - by Dmitri DB

  Long time reader, first time poster. Big, appreciative thanks for everyone's collective questioning and answering here and at stackoverflow, it's helped me quite a lot over the time I've been learning answers through these sites! Apologies in advance if I didn't search hard enough on posts already up on this site to find out what I could do about this issue, but I thought I'd just reach out for the sake of trying at least once. I've experienced this issue while starting up my macports-installed version of irssi: 13:25 -!- Irssi: Error in script dispatch: 13:25 Can't locate lib.pm in @INC (@INC contains: /opt/local/lib/perl5/site_perl/5.12.4/darwin-multi-2level /opt/local/lib/perl5/site_perl/5.12.4 /opt/local/lib/perl5/vendor_perl/5.12.4/darwin-multi-2level /opt/local/lib/perl5/vendor_perl/5.12.4 /opt/local/lib/perl5/5.12.4/darwin-multi-2level /opt/local/lib/perl5/5.12.4 /opt/local/lib/perl5/site_perl/5.12.3/darwin-multi-2level /opt/local/lib/perl5/site_perl/5.12.3 /opt/local/lib/perl5/site_perl /opt/local/lib/perl5/vendor_perl .) at (eval 18) line 1. 13:25 BEGIN failed--compilation aborted at (eval 18) line 1. 13:25 Huh, strange. I looked into it a bit: [email protected] /opt/local/lib/perl5 ?- find . -name "lib.pm" -ls 14673887 16 -r--r--r-- 1 root admin 6853 25 Jun 23:39 ./5.12.4/darwin-thread-multi- 2level/lib.pm [email protected] /opt/local/lib/perl5 ?- l 5.12.4/darwin-thread-multi-2level total 1864 drwxr-xr-x 55 root admin 1870 28 Jun 19:28 . drwxr-xr-x 158 root admin 5372 28 Jun 19:28 .. -rw-r--r-- 1 root admin 177814 25 Jun 23:39 .packlist drwxr-xr-x 6 root admin 204 28 Jun 19:28 B -r--r--r-- 1 root admin 25714 25 Jun 23:39 B.pm drwxr-xr-x 64 root admin 2176 28 Jun 19:28 CORE drwxr-xr-x 3 root admin 102 28 Jun 19:28 Compress -r--r--r-- 1 root admin 3000 25 Jun 23:39 Config.pm -r--r--r-- 1 root admin 228094 25 Jun 23:39 Config.pod -r--r--r-- 1 root admin 409 25 Jun 23:39 Config_git.pl -r--r--r-- 1 root admin 38759 25 Jun 23:39 Config_heavy.pl -r--r--r-- 1 root admin 21174 25 Jun 23:39 Cwd.pm -r--r--r-- 1 root admin 63535 25 Jun 23:39 DB_File.pm drwxr-xr-x 3 root admin 102 28 Jun 19:28 Data drwxr-xr-x 5 root admin 170 28 Jun 19:28 Devel drwxr-xr-x 4 root admin 136 28 Jun 19:28 Digest -r--r--r-- 1 root admin 25185 25 Jun 23:39 DynaLoader.pm drwxr-xr-x 22 root admin 748 28 Jun 19:28 Encode -r--r--r-- 1 root admin 29731 25 Jun 23:39 Encode.pm -r--r--r-- 1 root admin 6736 25 Jun 23:39 Errno.pm -r--r--r-- 1 root admin 5445 25 Jun 23:39 Fcntl.pm drwxr-xr-x 5 root admin 170 28 Jun 19:28 File drwxr-xr-x 3 root admin 102 28 Jun 19:28 Filter -r--r--r-- 1 root admin 1819 25 Jun 23:39 GDBM_File.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Hash drwxr-xr-x 3 root admin 102 28 Jun 19:28 I18N drwxr-xr-x 11 root admin 374 28 Jun 19:28 IO -r--r--r-- 1 root admin 1404 25 Jun 23:39 IO.pm drwxr-xr-x 6 root admin 204 28 Jun 19:28 IPC drwxr-xr-x 4 root admin 136 28 Jun 19:28 List drwxr-xr-x 4 root admin 136 28 Jun 19:28 MIME drwxr-xr-x 3 root admin 102 28 Jun 19:28 Math -r--r--r-- 1 root admin 2519 25 Jun 23:39 NDBM_File.pm -r--r--r-- 1 root admin 4208 25 Jun 23:39 O.pm -r--r--r-- 1 root admin 15563 25 Jun 23:39 Opcode.pm -r--r--r-- 1 root admin 21011 25 Jun 23:39 POSIX.pm -r--r--r-- 1 root admin 58962 25 Jun 23:39 POSIX.pod drwxr-xr-x 5 root admin 170 28 Jun 19:28 PerlIO -r--r--r-- 1 root admin 2515 25 Jun 23:39 SDBM_File.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Scalar -r--r--r-- 1 root admin 10837 25 Jun 23:39 Socket.pm -r--r--r-- 1 root admin 41003 25 Jun 23:39 Storable.pm drwxr-xr-x 4 root admin 136 28 Jun 19:28 Sys drwxr-xr-x 3 root admin 102 28 Jun 19:28 Text drwxr-xr-x 5 root admin 170 28 Jun 19:28 Time drwxr-xr-x 3 root admin 102 28 Jun 19:28 Unicode -r--r--r-- 1 root admin 14462 25 Jun 23:39 attributes.pm drwxr-xr-x 38 root admin 1292 28 Jun 19:28 auto -r--r--r-- 1 root admin 19892 25 Jun 23:39 encoding.pm -r--r--r-- 1 root admin 6853 25 Jun 23:39 lib.pm -r--r--r-- 1 root admin 11044 25 Jun 23:39 mro.pm -r--r--r-- 1 root admin 997 25 Jun 23:39 ops.pm -r--r--r-- 1 root admin 13945 25 Jun 23:39 re.pm drwxr-xr-x 3 root admin 102 28 Jun 19:28 threads -r--r--r-- 1 root admin 33283 25 Jun 23:39 threads.pm So, it sort of seems to me that the permissions which perl5 got installed with for these modules has gotten mixed up somehow? I'm not really a perl user beyond enjoying it for massive directory-recursive find/replace operations within text files, so I haven't much of an idea what the permissions here are supposed to look like, and I'm not really sure how to go about determining how macports has gone and installed perl this way when it's otherwise worked without failure for years now. Does anyone have any recommendations for the sanest path towards rectifying this issue? Also, is there any interesting reason as to why the macports default for the perl5 port installs 5.12.4, and not 5.16.0, which has to be explicitly installed via the perl5.16 port? Thanks again!

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• Can the STREAM and GUPS (single CPU) benchmark use non-local memory in NUMA machine

  - by osgx

  Hello I want to run some tests from HPCC, STREAM and GUPS. They will test memory bandwidth, latency, and throughput (in term of random accesses). Can I start Single CPU test STREAM or Single CPU GUPS on NUMA node with memory interleaving enabled? (Is it allowed by the rules of HPCC - High Performance Computing Challenge?) Usage of non-local memory can increase GUPS results, because it will increase 2- or 4- fold the number of memory banks, available for random accesses. (GUPS typically limited by nonideal memory-subsystem and by slow memory bank opening/closing. With more banks it can do update to one bank, while the other banks are opening/closing.) Thanks. UPDATE: (you may nor reorder the memory accesses that the program makes). But can compiler reorder loops nesting? E.g. hpcc/RandomAccess.c /* Perform updates to main table. The scalar equivalent is: * * u64Int ran; * ran = 1; * for (i=0; i<NUPDATE; i++) { * ran = (ran << 1) ^ (((s64Int) ran < 0) ? POLY : 0); * table[ran & (TableSize-1)] ^= stable[ran >> (64-LSTSIZE)]; * } */ for (j=0; j<128; j++) ran[j] = starts ((NUPDATE/128) * j); for (i=0; i<NUPDATE/128; i++) { /* #pragma ivdep */ for (j=0; j<128; j++) { ran[j] = (ran[j] << 1) ^ ((s64Int) ran[j] < 0 ? POLY : 0); Table[ran[j] & (TableSize-1)] ^= stable[ran[j] >> (64-LSTSIZE)]; } } The main loop here is for (i=0; i<NUPDATE/128; i++) { and the nested loop is for (j=0; j<128; j++) {. Using 'loop interchange' optimization, compiler can convert this code to for (j=0; j<128; j++) { for (i=0; i<NUPDATE/128; i++) { ran[j] = (ran[j] << 1) ^ ((s64Int) ran[j] < 0 ? POLY : 0); Table[ran[j] & (TableSize-1)] ^= stable[ran[j] >> (64-LSTSIZE)]; } } It can be done because this loop nest is perfect loop nest. Is such optimization prohibited by rules of HPCC?

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• Overriding Object.Equals() instance method in C#; now Code Analysis / FxCop warning CA2218: "should

  - by Chris W. Rea

  I've got a complex class in my C# project on which I want to be able to do equality tests. It is not a trivial class; it contains a variety of scalar properties as well as references to other objects and collections (e.g. IDictionary). For what it's worth, my class is sealed. To enable a performance optimization elsewhere in my system (an optimization that avoids a costly network round-trip), I need to be able to compare instances of these objects to each other for equality – other than the built-in reference equality – and so I'm overriding the Object.Equals() instance method. However, now that I've done that, Visual Studio 2008's Code Analysis a.k.a. FxCop, which I keep enabled by default, is raising the following warning: warning : CA2218 : Microsoft.Usage : Since 'MySuperDuperClass' redefines Equals, it should also redefine GetHashCode. I think I understand the rationale for this warning: If I am going to be using such objects as the key in a collection, the hash code is important. i.e. see this question. However, I am not going to be using these objects as the key in a collection. Ever. Feeling justified to suppress the warning, I looked up code CA2218 in the MSDN documentation to get the full name of the warning so I could apply a SuppressMessage attribute to my class as follows: [SuppressMessage("Microsoft.Naming", "CA2218:OverrideGetHashCodeOnOverridingEquals", Justification="This class is not to be used as key in a hashtable.")] However, while reading further, I noticed the following: How to Fix Violations To fix a violation of this rule, provide an implementation of GetHashCode. For a pair of objects of the same type, you must ensure that the implementation returns the same value if your implementation of Equals returns true for the pair. When to Suppress Warnings ----- Do not suppress a warning from this rule. [arrow & emphasis mine] So, I'd like to know: Why shouldn't I suppress this warning as I was planning to? Doesn't my case warrant suppression? I don't want to code up an implementation of GetHashCode() for this object that will never get called, since my object will never be the key in a collection. If I wanted to be pedantic, instead of suppressing, would it be more reasonable for me to override GetHashCode() with an implementation that throws a NotImplementedException? Update: I just looked this subject up again in Bill Wagner's good book Effective C#, and he states in "Item 10: Understand the Pitfalls of GetHashCode()": If you're defining a type that won't ever be used as the key in a container, this won't matter. Types that represent window controls, web page controls, or database connections are unlikely to be used as keys in a collection. In those cases, do nothing. All reference types will have a hash code that is correct, even if it is very inefficient. [...] In most types that you create, the best approach is to avoid the existence of GetHashCode() entirely. ... that's where I originally got this idea that I need not be concerned about GetHashCode() always.

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• Syntax error in INSERT INTO statement

  - by user454563

  I wrote a program that connects to MS Access. When I fill in the fields and add a new item to Access the program fails. The exception is "Syntax error in INSERT INTO statement" Here is the relevant code. **************************************************************** AdoHelper.cs **************************************************************** using System; using System.Collections.Generic; using System.Text; using System.Data; using System.Data.OleDb; namespace Yad2 { class AdoHelper { //get the connection string from the app.config file //Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Yad2.accdb static string connectionString = Properties.Settings.Default.DBConnection.ToString(); //declare the db connection static OleDbConnection con = new OleDbConnection(connectionString); /// <summary> /// To Execute queries which returns result set (table / relation) /// </summary> /// <param name="query">the query string</param> /// <returns></returns> public static DataTable ExecuteDataTable(string query) { try { con.Open(); OleDbCommand command = new OleDbCommand(query, con); System.Data.OleDb.OleDbDataAdapter tableAdapter = new System.Data.OleDb.OleDbDataAdapter(command); DataTable dt = new DataTable(); tableAdapter.Fill(dt); return dt; } catch (Exception ex) { throw ex; } finally { con.Close(); } } /// <summary> /// To Execute update / insert / delete queries /// </summary> /// <param name="query">the query string</param> public static void ExecuteNonQuery(string query) { try { con.Open(); System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand(query, con); command.ExecuteNonQuery(); } catch (Exception ex) { throw ex; } finally { con.Close(); } } /// <summary> /// To Execute queries which return scalar value /// </summary> /// <param name="query">the query string</param> public static object ExecuteScalar(string query) { try { con.Open(); System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand(query, con); /// here is the Excaption !!!!!!!!! return command.ExecuteScalar(); } catch { throw; } finally { con.Close(); } } } } **************************************************************************** **************************************************************************** DataQueries.cs **************************************************************************** using System; using System.Collections.Generic; using System.Text; using System.Data; namespace Yad2 { class DataQueries { public static DataTable GetAllItems() { try { string query = "Select * from Messages"; DataTable dt = AdoHelper.ExecuteDataTable(query); return dt; } catch (Exception ex) { throw ex; } } public static void AddNewItem(string mesNumber, string title , string mesDate , string contactMail , string mesType , string Details ) { string query = "Insert into Messages values(" + mesNumber + " , '" + title + "' , '" + mesDate + "' , '" + contactMail + "' , , '" + mesType + "' , '" + Details + "')"; AdoHelper.ExecuteNonQuery(query); } public static void DeleteDept(int mesNumber) { string query = "Delete from Item where MessageNumber=" + mesNumber; AdoHelper.ExecuteNonQuery(query); } } } *********************************************************************************************** plase help me .... why the program falls ?

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• Entity Association Mapping with Code First Part 1 : Mapping Complex Types

  - by mortezam

  Last week the CTP5 build of the new Entity Framework Code First has been released by data team at Microsoft. Entity Framework Code-First provides a pretty powerful code-centric way to work with the databases. When it comes to associations, it brings ultimate flexibility. I’m a big fan of the EF Code First approach and am planning to explain association mapping with code first in a series of blog posts and this one is dedicated to Complex Types. If you are new to Code First approach, you can find a great walkthrough here. In order to build a solid foundation for our discussion, we will start by learning about some of the core concepts around the relationship mapping.   What is Mapping?Mapping is the act of determining how objects and their relationships are persisted in permanent data storage, in our case, relational databases. What is Relationship mapping?A mapping that describes how to persist a relationship (association, aggregation, or composition) between two or more objects. Types of RelationshipsThere are two categories of object relationships that we need to be concerned with when mapping associations. The first category is based on multiplicity and it includes three types: One-to-one relationships: This is a relationship where the maximums of each of its multiplicities is one. One-to-many relationships: Also known as a many-to-one relationship, this occurs when the maximum of one multiplicity is one and the other is greater than one. Many-to-many relationships: This is a relationship where the maximum of both multiplicities is greater than one. The second category is based on directionality and it contains two types: Uni-directional relationships: when an object knows about the object(s) it is related to but the other object(s) do not know of the original object. To put this in EF terminology, when a navigation property exists only on one of the association ends and not on the both. Bi-directional relationships: When the objects on both end of the relationship know of each other (i.e. a navigation property defined on both ends). How Object Relationships Are Implemented in POCO domain models?When the multiplicity is one (e.g. 0..1 or 1) the relationship is implemented by defining a navigation property that reference the other object (e.g. an Address property on User class). When the multiplicity is many (e.g. 0..*, 1..*) the relationship is implemented via an ICollection of the type of other object. How Relational Database Relationships Are Implemented? Relationships in relational databases are maintained through the use of Foreign Keys. A foreign key is a data attribute(s) that appears in one table and must be the primary key or other candidate key in another table. With a one-to-one relationship the foreign key needs to be implemented by one of the tables. To implement a one-to-many relationship we implement a foreign key from the “one table” to the “many table”. We could also choose to implement a one-to-many relationship via an associative table (aka Join table), effectively making it a many-to-many relationship. Introducing the ModelNow, let's review the model that we are going to use in order to implement Complex Type with Code First. It's a simple object model which consist of two classes: User and Address. Each user could have one billing address. The Address information of a User is modeled as a separate class as you can see in the UML model below: In object-modeling terms, this association is a kind of aggregation—a part-of relationship. Aggregation is a strong form of association; it has some additional semantics with regard to the lifecycle of objects. In this case, we have an even stronger form, composition, where the lifecycle of the part is fully dependent upon the lifecycle of the whole. Fine-grained domain models The motivation behind this design was to achieve Fine-grained domain models. In crude terms, fine-grained means “more classes than tables”. For example, a user may have both a billing address and a home address. In the database, you may have a single User table with the columns BillingStreet, BillingCity, and BillingPostalCode along with HomeStreet, HomeCity, and HomePostalCode. There are good reasons to use this somewhat denormalized relational model (performance, for one). In our object model, we can use the same approach, representing the two addresses as six string-valued properties of the User class. But it’s much better to model this using an Address class, where User has the BillingAddress and HomeAddress properties. This object model achieves improved cohesion and greater code reuse and is more understandable. Complex Types: Splitting a Table Across Multiple Types Back to our model, there is no difference between this composition and other weaker styles of association when it comes to the actual C# implementation. But in the context of ORM, there is a big difference: A composed class is often a candidate Complex Type. But C# has no concept of composition—a class or property can’t be marked as a composition. The only difference is the object identifier: a complex type has no individual identity (i.e. no AddressId defined on Address class) which make sense because when it comes to the database everything is going to be saved into one single table. How to implement a Complex Types with Code First Code First has a concept of Complex Type Discovery that works based on a set of Conventions. The convention is that if Code First discovers a class where a primary key cannot be inferred, and no primary key is registered through Data Annotations or the fluent API, then the type will be automatically registered as a complex type. Complex type detection also requires that the type does not have properties that reference entity types (i.e. all the properties must be scalar types) and is not referenced from a collection property on another type. Here is the implementation: public class User{    public int UserId { get; set; }    public string FirstName { get; set; }    public string LastName { get; set; }    public string Username { get; set; }    public Address Address { get; set; }} public class Address {     public string Street { get; set; }     public string City { get; set; }            public string PostalCode { get; set; }        }public class EntityMappingContext : DbContext {     public DbSet<User> Users { get; set; }        } With code first, this is all of the code we need to write to create a complex type, we do not need to configure any additional database schema mapping information through Data Annotations or the fluent API. Database SchemaThe mapping result for this object model is as follows: Limitations of this mappingThere are two important limitations to classes mapped as Complex Types: Shared references is not possible: The Address Complex Type doesn’t have its own database identity (primary key) and so can’t be referred to by any object other than the containing instance of User (e.g. a Shipping class that also needs to reference the same User Address). No elegant way to represent a null reference There is no elegant way to represent a null reference to an Address. When reading from database, EF Code First always initialize Address object even if values in all mapped columns of the complex type are null. This means that if you store a complex type object with all null property values, EF Code First returns a initialized complex type when the owning entity object is retrieved from the database. SummaryIn this post we learned about fine-grained domain models which complex type is just one example of it. Fine-grained is fully supported by EF Code First and is known as the most important requirement for a rich domain model. Complex type is usually the simplest way to represent one-to-one relationships and because the lifecycle is almost always dependent in such a case, it’s either an aggregation or a composition in UML. In the next posts we will revisit the same domain model and will learn about other ways to map a one-to-one association that does not have the limitations of the complex types. References ADO.NET team blog Mapping Objects to Relational Databases Java Persistence with Hibernate

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• Entity Framework v1 &hellip; Brief Synopsis and Tips &ndash; Part 2

  - by Rohit Gupta

  Using Entity Framework with ASMX Web sErvices and WCF Web Service: If you use ASMX WebService to expose Entity objects from Entity Framework... then the ASMX Webservice does not  include object graphs, one work around is to use Facade pattern or to use WCF Service. The other important aspect of using ASMX Web Services along with Entity Framework is that the ASMX Client is not aware of the existence of EF v1 since the client solely deals with C# objects (not EntityObjects or ObjectContext). Since the client is not aware of the ObjectContext hence the client cannot participate in change tracking since the client only receives the Current Values and not the Orginal values when the service sends the the Entity objects to the client. Thus there are 2 drawbacks to using EntityFramework with ASMX Web Service: 1. Object state is not maintained... so to overcome this limitation we need insert/update single entity at a time and retrieve the original values for the entity being updated on the server/service end before calling Save Changes. 2. ASMX does not maintain object graphs... i.e. Customer.Reservations or Customer.Reservations.Trip relationships are not maintained. Thus you need to send these relationships separately from service to client. WCF Web Service overcomes the object graph limitation of ASMX Web Service, but we need to insure that we are populating all the non-null scalar properties of all the objects in the object graph before calling Update. WCF Web service still cannot overcome the second limitation of tracking changes to entities at the client end. Also note that the "Customer" class in the Client is very different from the "Customer" class in the Entity Framework Model Entities. They are incompatible with each other hence we cannot cast one to the other. However the .NET Framework translates the client "Customer" Entity to the EFv1 Model "customer" Entity once the entity is serialzed back on the ASMX server end. If you need change tracking enabled on the client then we need to use WCF Data Services which is available with VS 2010. ====================================================================================================== In WCF when adding an object that has relationships, the framework assumes that every object in the object graph needs to be added to store. for e.g. in a Customer.Reservations.Trip object graph, when a Customer Entity is added to the store, the EFv1 assumes that it needs to a add a Reservations collection and also Trips for each Reservation. Thus if we need to use existing Trips for reservations then we need to insure that we null out the Trip object reference from Reservations and set the TripReference to the EntityKey of the desired Trip instead. ====================================================================================================== Understanding Relationships and Associations in EFv1 The Golden Rule of EF is that it does not load entities/relationships unless you ask it to explicitly do so. However there is 1 exception to this rule. This exception happens when you attach/detach entities from the ObjectContext. If you detach an Entity in a ObjectGraph from the ObjectContext, then the ObjectContext removes the ObjectStateEntry for this Entity and all the relationship Objects associated with this Entity. For e.g. in a Customer.Order.OrderDetails if the Customer Entity is detached from the ObjectContext then you cannot traverse to the Order and OrderDetails Entities (that still exist in the ObjectContext) from the Customer Entity(which does not exist in the Object Context) Conversely, if you JOIN a entity that is not in the ObjectContext with a Entity that is in the ObjContext then the First Entity will automatically be added to the ObjContext since relationships for the 2 Entities need to exist in the ObjContext. ========================================================= You cannot attach an EntityCollection to an entity through its navigation property for e.g. you cannot code myContact.Addresses = myAddressEntityCollection ========================================================== Cascade Deletes in EDM: The Designer does not support specifying cascase deletes for a Entity. To enable cascasde deletes on a Entity in EDM use the Association definition in CSDL for the Entity. for e.g. SalesOrderDetail (SOD) has a Foreign Key relationship with SalesOrderHeader (SalesOrderHeader 1 : SalesOrderDetail *) if you specify a cascade Delete on SalesOrderHeader Entity then calling deleteObject on SalesOrderHeader (SOH) Entity will send delete commands for SOH record and all the SOD records that reference the SOH record. ========================================================== As a good design practise, if you use Cascade Deletes insure that Cascade delete facet is used both in the EDM as well as in the database. Even though it is not absolutely mandatory to have Cascade deletes on both Database and EDM (since you can see that just the Cascade delete spec on the SOH Entity in EDM will insure that SOH record and all related SOD records will be deleted from the database ... even though you dont have cascade delete configured in the database in the SOD table) ============================================================== Maintaining relationships in Code When Setting a Navigation property of a Entity (for e.g. setting the Contact Navigation property of Address Entity) the following rules apply : If both objects are detached, no relationship object will be created. You are simply setting a property the CLR way. If both objects are attached, a relationship object will be created. If only one of the objects is attached, the other will become attached and a relationship object will be created. If that detached object is new, when it is attached to the context its EntityState will be Added. One important rule to remember regarding synchronizing the EntityReference.Value and EntityReference.EntityKey properties is that when attaching an Entity which has a EntityReference (e.g. Address Entity with ContactReference) the Value property will take precedence and if the Value and EntityKey are out of sync, the EntityKey will be updated to match the Value. ====================================================== If you call .Load() method on a detached Entity then the .Load() operation will throw an exception. There is one exception to this rule. If you load entities using MergeOption.NoTracking, you will be able to call .Load() on such entities since these Entities are accessible by the ObjectContext. So the bottomline is that we need Objectontext to be able to call .Load() method to do deffered loading on EntityReference or EntityCollection. Another rule to remember is that you cannot call .Load() on entities that have a EntityState.Added State since the ObjectContext uses the EntityKey of the Primary (Parent) Entity when loading the related (Child) Entity (and not the EntityKey of the child (even if the EntityKey of the child is present before calling .Load()) ====================================================== You can use ObjContext.Add() to add a entity to the ObjContext and set the EntityState of the new Entity to EntityState.Added. here no relationships are added/updated. You can also use EntityCollection.Add() method to add an entity to another entity's related EntityCollection for e.g. contact has a Addresses EntityCollection so to add a new address use contact.Addresses.Add(newAddress) to add a new address to the Addresses EntityCollection. Note that if the entity does not already exist in the ObjectContext then calling contact.Addresses.Add(myAddress) will cause a new Address Entity to be added to the ObjContext with EntityState.Added and it will also add a RelationshipEntry (a relationship object) with EntityState.Added which connects the Contact (contact) with the new address newAddress. Note that if the entity already exists in the Objectcontext (being part theOtherContact.Addresses Collection), then calling contact.Addresses.Add(existingAddress) will add 2 RelationshipEntry objects to the ObjectStateEntry Collection, one with EntityState.Deleted and the other with EntityState.Added. This implies that the existingAddress Entity is removed from the theOtherContact.Addresses Collection and Added to the contact.Addresses Collection..effectively reassigning the address entity from the theOtherContact to "contact". This is called moving an existing entity to a new object graph. ====================================================== You usually use ObjectContext.Attach() and EntityCollection.Attach() methods usually when you need to reconstruct the ObjectGraph after deserializing the objects as received from a ASMX Web Service Client. Attach is usually used to connect existing Entities in the ObjectContext. When EntityCollection.Attach() is called the EntityState of the RelationshipEntry (the relationship object) remains as EntityState.unchanged whereas when EntityCollection.Add() method is called the EntityState of the relationship object changes to EntityState.Added or EntityState.Deleted as the situation demands. ========================================================= LINQ To Entities Tips: Select Many does Inner Join by default.   for e.g. from c in Contact from a in c.Address select c ... this will do a Inner Join between the Contacts and Addresses Table and return only those Contacts that have a Address. ======================================================== Group Joins Do LEFT Join by default. e.g. from a in Address join c in Contact ON a.Contact.ContactID == c.ContactID Into g WHERE a.CountryRegion == "US" select g; This query will do a left join on the Contact table and return contacts that have a address in "US" region The following query : from c in Contact join a in Address.Where(a1 => a1.CountryRegion == "US") on c.ContactID  equals a.Contact.ContactID into addresses select new {c, addresses} will do a left join on the Address table and return All Contacts. In these Contacts only those will have its Address EntityCollection Populated which have a Address in the "US" region, the other contacts will have 0 Addresses in the Address collection (even if addresses for those contacts exist in the database but are in a different region) ======================================================== Linq to Entities does not support DefaultIfEmpty().... instead use .Include("Address") Query Builder method to do a Left JOIN or use Group Joins if you need more control like Filtering on the Address EntityCollection of Contact Entity =================================================================== Use CreateSourceQuery() on the EntityReference or EntityCollection if you need to add filters during deferred loading of Entities (Deferred loading in EFv1 happens when you call Load() method on the EntityReference or EntityCollection. for e.g. var cust=context.Contacts.OfType<Customer>().First(); var sq = cust.Reservations.CreateSourceQuery().Where(r => r.ReservationDate > new DateTime(2008,1,1)); cust.Reservations.Attach(sq); This populates only those reservations that are older than Jan 1 2008. This is the only way (in EFv1) to Attach a Range of Entities to a EntityCollection using the Attach() method ================================================================== If you need to get the Foreign Key value for a entity e.g. to get the ContactID value from a Address Entity use this :                                address.ContactReference.EntityKey.EntityKeyValues.Where(k=> k.Key == "ContactID")

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• Silverlight animation not smooth

  - by Andrej

  Hi, When trying to animate objects time/frame based in Silverlight (in contrast to using something like DoubleAnimation or Storyboard, which is not suitable e.g. for fast paced games), for example moving a spaceship in a particular direction every frame, the movement is jumpy and not really smooth. The screen even seems to tear. There seems to be no difference between CompositionTarget and DistpatcherTimer. I use the following approach (in pseudocode): Register Handler to Tick-Event of a DispatcherTimer In each Tick: Compute the elapsed time from the last frame in milliseconds Object.X += movementSpeed * ellapsedMilliseconds This should result in a smooth movement, right? But it doesn't. Here is an example (Controls: WASD and Mouse): Silverlight Game. Although the effect I described is not too prevalent in this sample, I can assure you that even moving a single rectangle over a canvas produces a jumpy animation. Does someone have an idea how to minimize this. Are there other approaches to to frame based animation exept using Storyboards/DoubleAnimations which could solve this? Edit: Here a quick and dirty approach, animating a rectangle with minimum code (Controls: A and D) Animation Sample Xaml: <Grid x:Name="LayoutRoot" Background="Black"> <Canvas Width="1000" Height="400" Background="Blue"> <Rectangle x:Name="rect" Width="48" Height="48" Fill="White" Canvas.Top="200" Canvas.Left="0"/> </Canvas> </Grid> C#: private bool isLeft = false; private bool isRight = false; private DispatcherTimer timer = new DispatcherTimer(); private double lastUpdate; public Page() { InitializeComponent(); timer.Interval = TimeSpan.FromMilliseconds(1); timer.Tick += OnTick; lastUpdate = Environment.TickCount; timer.Start(); } private void OnTick(object sender, EventArgs e) { double diff = Environment.TickCount - lastUpdate; double x = Canvas.GetLeft(rect); if (isRight) x += 1 * diff; else if (isLeft) x -= 1 * diff; Canvas.SetLeft(rect, x); lastUpdate = Environment.TickCount; } private void UserControl_KeyDown(object sender, KeyEventArgs e) { if (e.Key == Key.D) isRight = true; if (e.Key == Key.A) isLeft = true; } private void UserControl_KeyUp(object sender, KeyEventArgs e) { if (e.Key == Key.D) isRight = false; if (e.Key == Key.A) isLeft = false; } Thanks! Andrej

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• How to optimize my PageRank calculation?

  - by asmaier

  In the book Programming Collective Intelligence I found the following function to compute the PageRank: def calculatepagerank(self,iterations=20): # clear out the current PageRank tables self.con.execute("drop table if exists pagerank") self.con.execute("create table pagerank(urlid primary key,score)") self.con.execute("create index prankidx on pagerank(urlid)") # initialize every url with a PageRank of 1.0 self.con.execute("insert into pagerank select rowid,1.0 from urllist") self.dbcommit() for i in range(iterations): print "Iteration %d" % i for (urlid,) in self.con.execute("select rowid from urllist"): pr=0.15 # Loop through all the pages that link to this one for (linker,) in self.con.execute("select distinct fromid from link where toid=%d" % urlid): # Get the PageRank of the linker linkingpr=self.con.execute("select score from pagerank where urlid=%d" % linker).fetchone()[0] # Get the total number of links from the linker linkingcount=self.con.execute("select count(*) from link where fromid=%d" % linker).fetchone()[0] pr+=0.85*(linkingpr/linkingcount) self.con.execute("update pagerank set score=%f where urlid=%d" % (pr,urlid)) self.dbcommit() However, this function is very slow, because of all the SQL queries in every iteration >>> import cProfile >>> cProfile.run("crawler.calculatepagerank()") 2262510 function calls in 136.006 CPU seconds Ordered by: standard name ncalls tottime percall cumtime percall filename:lineno(function) 1 0.000 0.000 136.006 136.006 <string>:1(<module>) 1 20.826 20.826 136.006 136.006 searchengine.py:179(calculatepagerank) 21 0.000 0.000 0.528 0.025 searchengine.py:27(dbcommit) 21 0.528 0.025 0.528 0.025 {method 'commit' of 'sqlite3.Connecti 1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler 1339864 112.602 0.000 112.602 0.000 {method 'execute' of 'sqlite3.Connec 922600 2.050 0.000 2.050 0.000 {method 'fetchone' of 'sqlite3.Cursor' 1 0.000 0.000 0.000 0.000 {range} So I optimized the function and came up with this: def calculatepagerank2(self,iterations=20): # clear out the current PageRank tables self.con.execute("drop table if exists pagerank") self.con.execute("create table pagerank(urlid primary key,score)") self.con.execute("create index prankidx on pagerank(urlid)") # initialize every url with a PageRank of 1.0 self.con.execute("insert into pagerank select rowid,1.0 from urllist") self.dbcommit() inlinks={} numoutlinks={} pagerank={} for (urlid,) in self.con.execute("select rowid from urllist"): inlinks[urlid]=[] numoutlinks[urlid]=0 # Initialize pagerank vector with 1.0 pagerank[urlid]=1.0 # Loop through all the pages that link to this one for (inlink,) in self.con.execute("select distinct fromid from link where toid=%d" % urlid): inlinks[urlid].append(inlink) # get number of outgoing links from a page numoutlinks[urlid]=self.con.execute("select count(*) from link where fromid=%d" % urlid).fetchone()[0] for i in range(iterations): print "Iteration %d" % i for urlid in pagerank: pr=0.15 for link in inlinks[urlid]: linkpr=pagerank[link] linkcount=numoutlinks[link] pr+=0.85*(linkpr/linkcount) pagerank[urlid]=pr for urlid in pagerank: self.con.execute("update pagerank set score=%f where urlid=%d" % (pagerank[urlid],urlid)) self.dbcommit() This function is 20 times faster (but uses a lot more memory for all the temporary dictionaries) because it avoids the unnecessary SQL queries in every iteration: >>> cProfile.run("crawler.calculatepagerank2()") 64802 function calls in 6.950 CPU seconds Ordered by: standard name ncalls tottime percall cumtime percall filename:lineno(function) 1 0.004 0.004 6.950 6.950 <string>:1(<module>) 1 1.004 1.004 6.946 6.946 searchengine.py:207(calculatepagerank2 2 0.000 0.000 0.104 0.052 searchengine.py:27(dbcommit) 23065 0.012 0.000 0.012 0.000 {meth 'append' of 'list' objects} 2 0.104 0.052 0.104 0.052 {meth 'commit' of 'sqlite3.Connection 1 0.000 0.000 0.000 0.000 {meth 'disable' of '_lsprof.Profiler' 31298 5.809 0.000 5.809 0.000 {meth 'execute' of 'sqlite3.Connectio 10431 0.018 0.000 0.018 0.000 {method 'fetchone' of 'sqlite3.Cursor' 1 0.000 0.000 0.000 0.000 {range} But is it possible to further reduce the number of SQL queries to speed up the function even more?

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• Finding minimum cut-sets between bounded subgraphs

  - by Tore

  If a game map is partitioned into subgraphs, how to minimize edges between subgraphs? I have a problem, Im trying to make A* searches through a grid based game like pacman or sokoban, but i need to find "enclosures". What do i mean by enclosures? subgraphs with as few cut edges as possible given a maximum size and minimum size for number of vertices for each subgraph that act as a soft constraints. Alternatively you could say i am looking to find bridges between subgraphs, but its generally the same problem. Given a game that looks like this, what i want to do is find enclosures so that i can properly find entrances to them and thus get a good heuristic for reaching vertices inside these enclosures. So what i want is to find these colored regions on any given map. My Motivation The reason for me bothering to do this and not just staying content with the performance of a simple manhattan distance heuristic is that an enclosure heuristic can give more optimal results and i would not have to actually do the A* to get some proper distance calculations and also for later adding competitive blocking of opponents within these enclosures when playing sokoban type games. Also the enclosure heuristic can be used for a minimax approach to finding goal vertices more properly. A possible solution to the problem is the Kernighan-Lin algorithm: function Kernighan-Lin(G(V,E)): determine a balanced initial partition of the nodes into sets A and B do A1 := A; B1 := B compute D values for all a in A1 and b in B1 for (i := 1 to |V|/2) find a[i] from A1 and b[i] from B1, such that g[i] = D[a[i]] + D[b[i]] - 2*c[a][b] is maximal move a[i] to B1 and b[i] to A1 remove a[i] and b[i] from further consideration in this pass update D values for the elements of A1 = A1 / a[i] and B1 = B1 / b[i] end for find k which maximizes g_max, the sum of g[1],...,g[k] if (g_max > 0) then Exchange a[1],a[2],...,a[k] with b[1],b[2],...,b[k] until (g_max <= 0) return G(V,E) My problem with this algorithm is its runtime at O(n^2 * lg(n)), i am thinking of limiting the nodes in A1 and B1 to the border of each subgraph to reduce the amount of work done. I also dont understand the c[a][b] cost in the algorithm, if a and b do not have an edge between them is the cost assumed to be 0 or infinity, or should i create an edge based on some heuristic. Do you know what c[a][b] is supposed to be when there is no edge between a and b? Do you think my problem is suitable to use a multi level problem? Why or why not? Do you have a good idea for how to reduce the work done with the kernighan-lin algorithm for my problem?

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• spoj: runlength

  - by user285825

  For RLM problem of SPOJ: This is the problem: "Run-length encoding of a number replaces a run of digits (that is, a sequence of consecutive equivalent digits) with the number of digits followed by the digit itself. For example, 44455 would become 3425 (three fours, two fives). Note that run-length encoding does not necessarily shorten the length of the data: 11 becomes 21, and 42 becomes 1412. If a number has more than nine consecutive digits of the same type, the encoding is done greedily: each run grabs as many digits as it can, so 111111111111111 is encoded as 9161. Implement an integer arithmetic calculator that takes operands and gives results in run-length format. You should support addition, subtraction, multiplication, and division. You won't have to divide by zero or deal with negative numbers. Input/Output The input will consist of several test cases, one per line. For each test case, compute the run-length mathematics expression and output the original expression and the result, as shown in the examples. The (decimal) representation of all operands and results will fit in signed 64-bit integers." These are my testcases: input: 11 + 11 988726 - 978625 12 * 41 1124 / 1112 13 * 33 15 / 16 19222317121013161815142715181017 + 10 10 + 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 19222317121013161815142715181017 / 11 11 / 19222317121013161815142715181017 19222317121013161815142715181017 / 12 12 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 19222317121013161815142715181017 19222317121013161815142715181017 * 11 11 * 19222317121013161815142715181017 19222317121013161815142715181017 * 10 10 * 19222317121013161815142715181017 19222317121013161815142715181017 - 10 19222317121013161815142715181017 - 19222317121013161815142715181017 19222317121013161815142715181017 - 141621161816101118141217131817191014 19222317121013161815142715181017 - 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191014 141621161816101118141217131817191014 + 141621161816101118141217131817191013 141621161816101118141217131817191014 + 10 10 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 11 + 141621161816101118141217131817191013 141621161816101118141217131817191013 * 12 12 * 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191014 141621161816101118141217131817191013 - 141621161816101118141217131817191013 141621161816101118141217131817191013 - 10 141621161816101118141217131817191014 - 11 141621161816101118141217131817191014 - 141621161816101118141217131817191013 141621161816101118141217131817191014 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 141621161816101118141217131817191014 141621161816101118141217131817191013 / 141621161816101118141217131817191013 141621161816101118141217131817191014 * 11 11 * 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 11 / 141621161816101118141217131817191014 10 + 10 10 + 11 10 + 15 15 + 10 11 + 10 11 + 10 10 - 10 15 - 10 10 * 10 10 * 15 15 * 10 10 / 111213 output: 11 + 11 = 12 988726 - 978625 = 919111 12 * 41 = 42 1124 / 1112 = 1112 13 * 33 = 39 15 / 16 = 10 19222317121013161815142715181017 + 10 = 19222317121013161815142715181017 10 + 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 = 11 19222317121013161815142715181017 / 11 = 19222317121013161815142715181017 11 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 12 = 141621161816101118141217131817191013 12 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191013 = 12 141621161816101118141217131817191013 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 * 11 = 19222317121013161815142715181017 11 * 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 * 10 = 10 10 * 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 10 = 19222317121013161815142715181017 19222317121013161815142715181017 - 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 141621161816101118141217131817191014 = 141621161816101118141217131817191013 19222317121013161815142715181017 - 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 + 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191013 + 141621161816101118141217131817191014 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 141621161816101118141217131817191013 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 10 = 141621161816101118141217131817191014 10 + 141621161816101118141217131817191013 = 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 = 141621161816101118141217131817191014 11 + 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 * 12 = 19222317121013161815142715181016 12 * 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191014 - 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 - 141621161816101118141217131817191013 = 10 141621161816101118141217131817191013 - 10 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 11 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191013 / 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 * 11 = 141621161816101118141217131817191014 11 * 141621161816101118141217131817191014 = 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 = 141621161816101118141217131817191014 11 / 141621161816101118141217131817191014 = 10 10 + 10 = 10 10 + 11 = 11 10 + 15 = 15 15 + 10 = 15 11 + 10 = 11 11 + 10 = 11 10 - 10 = 10 15 - 10 = 15 10 * 10 = 10 10 * 15 = 10 15 * 10 = 10 10 / 111213 = 10 I am getting consistently wrong answer. I generated the above testcases trying to make them as representative as possible (boundary conditions, etc). I am not sure how to test it further. Some guidline would be really appreciated.

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• Difficulties getting GraphViz working as a library in C++

  - by DistortedLojik

  Am working on a program that will allow a graph of nodes to be displayed and then updated visually as the nodes themselves are updated. I am fairly new to Visual Studio 2010 and am following the GraphViz guide located at http://www.graphviz.org/pdf/libguide.pdf in order to get GraphViz working as a library. I have the following code which is taken straight from the pdf linked above. #include <graphviz\gvc.h> #include <graphviz\cdt.h> #include <graphviz\graph.h> #include <graphviz\pathplan.h> using namespace std; int main(int argc, char **argv) { Agraph_t *g; Agnode_t *n, *m; Agedge_t *e; Agsym_t *a; GVC_t *gvc; /* set up a graphviz context */ gvc = gvContext(); /* parse command line args - minimally argv[0] sets layout engine */ gvParseArgs(gvc, argc, argv); /* Create a simple digraph */ g = agopen("g", AGDIGRAPH); n = agnode(g, "n"); m = agnode(g, "m"); e = agedge(g, n, m); /* Set an attribute - in this case one that affects the visible rendering */ agsafeset(n, "color", "red", ""); /* Compute a layout using layout engine from command line args */ gvLayoutJobs(gvc, g); /* Write the graph according to -T and -o options */ gvRenderJobs(gvc, g); /* Free layout data */ gvFreeLayout(gvc, g); /* Free graph structures */ agclose(g); /* close output file, free context, and return number of errors */ return (gvFreeContext(gvc)); } After compiling I get the following errors which indicate that I do not have it correctly linked. 1>main.obj : error LNK2019: unresolved external symbol _gvFreeContext referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _agclose referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _gvFreeLayout referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _gvRenderJobs referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _gvLayoutJobs referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _agsafeset referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _agedge referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _agnode referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _agopen referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _gvParseArgs referenced in function _main 1>main.obj : error LNK2019: unresolved external symbol _gvContext referenced in function _main Within the VC++ Directories I have C:\Program Files (x86)\Graphviz2.26.3\include in the Include Directories and C:\Program Files (x86)\Graphviz2.26.3\lib\release\lib in the Library Directories Any help would be greatly appreciated to help get this working. Thank you.

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• Unable to verify body hash for DKIM

  - by Joshua

  I'm writing a C# DKIM validator and have come across a problem that I cannot solve. Right now I am working on calculating the body hash, as described in Section 3.7 Computing the Message Hashes. I am working with emails that I have dumped using a modified version of EdgeTransportAsyncLogging sample in the Exchange 2010 Transport Agent SDK. Instead of converting the emails when saving, it just opens a file based on the MessageID and dumps the raw data to disk. I am able to successfully compute the body hash of the sample email provided in Section A.2 using the following code: SHA256Managed hasher = new SHA256Managed(); ASCIIEncoding asciiEncoding = new ASCIIEncoding(); string rawFullMessage = File.ReadAllText(@"C:\Repositories\Sample-A.2.txt"); string headerDelimiter = "\r\n\r\n"; int headerEnd = rawFullMessage.IndexOf(headerDelimiter); string header = rawFullMessage.Substring(0, headerEnd); string body = rawFullMessage.Substring(headerEnd + headerDelimiter.Length); byte[] bodyBytes = asciiEncoding.GetBytes(body); byte[] bodyHash = hasher.ComputeHash(bodyBytes); string bodyBase64 = Convert.ToBase64String(bodyHash); string expectedBase64 = "2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8="; Console.WriteLine("Expected hash: {1}{0}Computed hash: {2}{0}Are equal: {3}", Environment.NewLine, expectedBase64, bodyBase64, expectedBase64 == bodyBase64); The output from the above code is: Expected hash: 2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8= Computed hash: 2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8= Are equal: True Now, most emails come across with the c=relaxed/relaxed setting, which requires you to do some work on the body and header before hashing and verifying. And while I was working on it (failing to get it to work) I finally came across a message with c=simple/simple which means that you process the whole body as is minus any empty CRLF at the end of the body. (Really, the rules for Body Canonicalization are quite ... simple.) Here is the real DKIM email with a signature using the simple algorithm (with only unneeded headers cleaned up). Now, using the above code and updating the expectedBase64 hash I get the following results: Expected hash: VnGg12/s7xH3BraeN5LiiN+I2Ul/db5/jZYYgt4wEIw= Computed hash: ISNNtgnFZxmW6iuey/3Qql5u6nflKPTke4sMXWMxNUw= Are equal: False The expected hash is the value from the bh= field of the DKIM-Signature header. Now, the file used in the second test is a direct raw output from the Exchange 2010 Transport Agent. If so inclined, you can view the modified EdgeTransportLogging.txt. At this point, no matter how I modify the second email, changing the start position or number of CRLF at the end of the file I cannot get the files to match. What worries me is that I have been unable to validate any body hash so far (simple or relaxed) and that it may not be feasible to process DKIM through Exchange 2010.

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• Understanding PTS and DTS in video frames

  - by theateist

  I had fps issues when transcoding from avi to mp4(x264). Eventually the problem was in PTS and DTS values, so lines 12-15 where added before av_interleaved_write_frame function: 1. AVFormatContext* outContainer = NULL; 2. avformat_alloc_output_context2(&outContainer, NULL, "mp4", "c:\\test.mp4"; 3. AVCodec *encoder = avcodec_find_encoder(AV_CODEC_ID_H264); 4. AVStream *outStream = avformat_new_stream(outContainer, encoder); 5. // outStream->codec initiation 6. // ... 7. avformat_write_header(outContainer, NULL); 8. // reading and decoding packet 9. // ... 10. avcodec_encode_video2(outStream->codec, &encodedPacket, decodedFrame, &got_frame) 11. 12. if (encodedPacket.pts != AV_NOPTS_VALUE) 13. encodedPacket.pts = av_rescale_q(encodedPacket.pts, outStream->codec->time_base, outStream->time_base); 14. if (encodedPacket.dts != AV_NOPTS_VALUE) 15. encodedPacket.dts = av_rescale_q(encodedPacket.dts, outStream->codec->time_base, outStream->time_base); 16. 17. av_interleaved_write_frame(outContainer, &encodedPacket) After reading many posts I still do not understand: outStream->codec->time_base = 1/25 and outStream->time_base = 1/12800. The 1st one was set by me but I cannot figure out why and who set 12800? I noticed that before line (7) outStream->time_base = 1/90000 and right after it it changes to 1/12800, why? When I transcode from avi to avi, meaning changing the line (2) to avformat_alloc_output_context2(&outContainer, NULL, "avi", "c:\\test.avi"; , so before and after line (7) outStream->time_base remains always 1/25 and not like in mp4 case, why? What is the difference between time_base of outStream->codec and outStream? To calc the pts av_rescale_q does: takes 2 time_base, multiplies their fractions in cross and then compute the pts. Why it does this in this way? As I debugged, the encodedPacket.pts has value incremental by 1, so why changing it if it does has value? At the beginning the dts value is -2 and after each rescaling it still has negative number, but despite this the video played correctly! Shouldn't it be positive?

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• adding array values

  - by christian

  Array ( [0] => Array ( [datas] => Array ( [name] => lorem [id] => 1 [type] => t1 [due_type] => Q1 [t1] => 1 [t2] => 1 [t3] => 1 ) ) [1] => Array ( [datas] => Array ( [name] => lorem [id] => 1 [type] => t2 [due_type] => Q1 [t1] => 0 [t2] => 1 [t3] => 0 ) ) [2] => Array ( [datas] => Array ( [name] => name [id] => 2 [type] => t1 [due_type] => Q1 [t1] => 1 [t2] => 0 [t3] => 1 ) ) [3] => Array ( [datas] => Array ( [name] => name [id] => 2 [type] => t2 [due_type] => Q1 [t1] => 1 [t2] => 0 [t3] => 0 ) ) ) I want to add the values of each array according to its id, but I am having problem getting the values using these code: I want to compute the sum of all type according to each due_type and combining them into one array. $totals = array(); $i = -1; foreach($datas as $key => $row){ $i += 1; $items[$i] = $row; if (isset($totals[$items[$i]['datas']['id']])){ if($totals[$items[$i]['datas']['id']]['due_type'] == 'Q1'){ if($totals[$items[$i]['datas']['id']]['type'] == 't1'){ $t1+=$totals[$items[$i]['datas']['id']]['t1']; }elseif($totals[$items[$i]['datas']['id']]['type'] == 't2'){ $t2+=$totals[$items[$i]['datas']['id']]['t2']; }elseif($totals[$items[$i]['datas']['id']]['type'] == 't3'){ $t3+=$totals[$items[$i]['datas']['id']]['t3']; } $totals[$items[$i]['datas']['id']]['t1_total'] = $t1; $totals[$items[$i]['datas']['id']]['t2_total'] = $t2; } } else { $totals[$items[$i]['datas']['id']] = $row['datas']; $totals[$items[$i]['datas']['id']]['t1_total'] = $items[$i]['datas']['t1']; $totals[$items[$i]['datas']['id']]['t2_total'] = $items[$i]['datas']['t2']; } }

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• Python/Biophysics- Trying to code a simple stochastic simulation!

  - by user359597

  Hey guys- I'm trying to figure out what to make of the following code- this is not the clear, intuitive python I've been learning. Was it written in C or something then wrapped in a python fxn? The code I wrote (not shown) is using the same math, but I couldn't figure out how to write a conditional loop. If anyone could explain/decipher/clean this up, I'd be really appreciative. I mean- is this 'good' python- or does it look funky? I'm brand new to this- but it's like the order of the fxns is messed up? I understand Gillespie's- I've successfully coded several simpler simulations. So in a nutshell- good code-(pythonic)? order? c? improvements? am i being an idiot? The code shown is the 'answer,' to the following question from a biophysics text (petri-net not shown and honestly not necessary to understand problem): "In a programming language of your choice, implement Gillespie’s First Reaction Algorithm to study the temporal behaviour of the reaction A---B in which the transition from A to B can only take place if another compound, C, is present, and where C dynamically interconverts with D, as modelled in the Petri-net below. Assume that there are 100 molecules of A, 1 of C, and no B or D present at the start of the reaction. Set kAB to 0.1 s-1 and both kCD and kDC to 1.0 s-1. Simulate the behaviour of the system over 100 s." def sim(): # Set the rate constants for all transitions kAB = 0.1 kCD = 1.0 kDC = 1.0 # Set up the initial state A = 100 B = 0 C = 1 D = 0 # Set the start and end times t = 0.0 tEnd = 100.0 print "Time\t", "Transition\t", "A\t", "B\t", "C\t", "D" # Compute the first interval transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) # Loop until the end time is exceded or no transition can fire any more while t <= tEnd and transition >= 0: print t, '\t', transition, '\t', A, '\t', B, '\t', C, '\t', D t += interval if transition == 0: A -= 1 B += 1 if transition == 1: C -= 1 D += 1 if transition == 2: C += 1 D -= 1 transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) def transitionData(A, B, C, D, kAB, kCD, kDC): """ Returns nTransition, the number of the firing transition (0: A->B, 1: C->D, 2: D->C), and interval, the interval between the time of the previous transition and that of the current one. """ RAB = kAB * A * C RCD = kCD * C RDC = kDC * D dt = [-1.0, -1.0, -1.0] if RAB > 0.0: dt[0] = -math.log(1.0 - random.random())/RAB if RCD > 0.0: dt[1] = -math.log(1.0 - random.random())/RCD if RDC > 0.0: dt[2] = -math.log(1.0 - random.random())/RDC interval = 1e36 transition = -1 for n in range(len(dt)): if dt[n] > 0.0 and dt[n] < interval: interval = dt[n] transition = n return transition, interval if __name__ == '__main__': sim()

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• Variable sized packet structs with vectors

  - by Rev316

  Lately I've been diving into network programming, and I'm having some difficulty constructing a packet with a variable "data" property. Several prior questions have helped tremendously, but I'm still lacking some implementation details. I'm trying to avoid using variable sized arrays, and just use a vector. But I can't get it to be transmitted correctly, and I believe it's somewhere during serialization. Now for some code. Packet Header class Packet { public: void* Serialize(); bool Deserialize(void *message); unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; }; Packet ImpL typedef struct { unsigned int sender_id; unsigned int sequence_number; std::vector<char> data; } Packet; void* Packet::Serialize(int size) { Packet* p = (Packet *) malloc(8 + 30); p->sender_id = htonl(this->sender_id); p->sequence_number = htonl(this->sequence_number); p->data.assign(size,'&'); //just for testing purposes } bool Packet::Deserialize(void *message) { Packet *s = (Packet*)message; this->sender_id = ntohl(s->sender_id); this->sequence_number = ntohl(s->sequence_number); this->data = s->data; } During execution, I simply create a packet, assign it's members, and send/receive accordingly. The above methods are only responsible for serialization. Unfortunately, the data never gets transferred. Couple of things to point out here. I'm guessing the malloc is wrong, but I'm not sure how else to compute it (i.e. what other value it would be). Other than that, I'm unsure of the proper way to use a vector in this fashion, and would love for someone to show me how (code examples please!) :) Edit: I've awarded the question to the most comprehensive answer regarding the implementation with a vector data property. Appreciate all the responses!

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