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• Best architecture for a social media app

  - by Sky

  Hey guys, Im working on promising project that develops a new social media app for web and mobile. We are at begin defining functionalities. Nevertheless, I'm thinking ahead on architecture. So I'm asking: 1 - Whats the best plataform to develop the core of this aplication that will have a Rest API interface. 2 - Whats the best database that will scale and grow with my application. As far as I researched, these were the answers I found most interesting: For database: Cassandra NoSQL DB, amazing scalabilty, amazing write performance, good read performance (will be improved on 0.6). I think i will choose that one. Zookeer for transactions on Cassandra. I think that 2 technologies rly good for that propose. What do you think guys? On the front end that will serve the REST API, i dont have a final candidate. For this one i have questions based on Perfomance X Scalabilty X Fast Development/Maintenance. Java or .Net As far as I researched, brings the best balance of this requisits. Python, pearl and Rail, has the best (Fast Development/Maintenance), but sux on all other. C or C++ I dont even consider, because its (Fast Development/Maintenance) sux... So what do you guy think about it?

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• How to recalculate all-pairs shorthest paths on-line if nodes are getting removed?

  - by Pavel Shved

  Latest news about underground bombing made me curious about the following problem. Assume we have a weighted undirected graph, nodes of which are sometimes removed. The problem is to re-calculate shortest paths between all pairs of nodes fast after such removals. With a simple modification of Floyd-Warshall algorithm we can calculate shortest paths between all pairs. These paths may be stored in a table, where shortest[i][j] contains the index of the next node on the shortest path between i and j (or NULL value if there's no path). The algorithm requires O(n³) time to build the table, and eacho query shortest(i,j) takes O(1). Unfortunately, we should re-run this algorithm after each removal. The other alternative is to run graph search on each query. This way each removal takes zero time to update an auxiliary structure (because there's none), but each query takes O(E) time. What algorithm can be used to "balance" the query and update time for all-pairs shortest-paths problem when nodes of the graph are being removed?

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• Is ASP.NET MVC is really MVC? Or how to separate model from controller?

  - by Andrey

  Hi all, This question is a bit rhetorical. At some point i got a feeling that ASP.NET MVC is not that authentic implementation of MVC pattern. Or i didn't understood it. Consider following domain: electric bulb, switch and motion detector. They are connected together and when you enter the room motion detector switches on the bulb. If i want to represent them as MVC: switch is model, because it holds the state and contains logic bulb is view, because it presents the state of model to human motion detector is controller, because it converts user actions to generic model commands Switch has one private field (On/Off) as a State and two methods (PressOn, PressOff). If you call PressOn when it is Off it goes to On, if you call it again state doesn't change. Bulb can be replaced with buzzer, motion detector with timer or button, but the model still represent the same logic. Eventually system will have same behavior. This is how i understand classical MVC decomposition, please correct me if i am wrong. Now let's decompose it in ASP.Net MVC way. Bulb is still a view Controller will be switch + motion detector Model is some object that will just pass state to bulb. So the logic that defines behavior moves to controller. Question 1: Is my understanding of MVC and ASP.NET MVC correct? Question 2: If yes, do you agree that ASP.NET MVC is not 100% accurate implementation? And back to life. The final question is how to separate model from controller in case of ASP.NET MVC. There can be two extremes. Controller does basic stuff and call model to do all the logic. Another is controller does all the logic and model is just something like class with properties that is mapped to DB. Question 3: Where should i draw the line between this extremes? How to balance? Thanks, Andrey

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• Looking for advice on importing large dataset in sqlite and Cocoa/Objective-C

  - by jluckyiv

  I have a fairly large hierarchical dataset I'm importing. The total size of the database after import is about 270MB in sqlite. My current method works, but I know I'm hogging memory as I do it. For instance, if I run with Zombies, my system freezes up (although it will execute just fine if I don't use that Instrument). I was hoping for some algorithm advice. I have three hierarchical tables comprising about 400,000 records. The highest level has about 30 records, the next has about 20,000, the last has the balance. Right now, I'm using nested for loops to import. I know I'm creating an unreasonably large object graph, but I'm also looking to serialize to JSON or XML because I want to break up the records into downloadable chunks for the end user to import a la carte. I have the code written to do the serialization, but I'm wondering if I can serialize the object graph if I only have pieces in memory. Here's pseudocode showing the basic process for sqlite import. I left out the unnecessary detail. [database open]; [database beginTransaction]; NSArray *firstLevels = [[FirstLevel fetchFromURL:url retain]; for (FirstLevel *firstLevel in firstLevels) { [firstLevel save]; int id1 = [firstLevel primaryKey]; NSArray *secondLevels = [[SecondLevel fetchFromURL:url] retain]; for (SecondLevel *secondLevel in secondLevels) { [secondLevel saveWithForeignKey:id1]; int id2 = [secondLevel primaryKey]; NSArray *thirdLevels = [[ThirdLevel fetchFromURL:url] retain]; for (ThirdLevel *thirdLevel in thirdLevels) { [thirdLevel saveWithForeignKey:id2]; } [database commit]; [database beginTransaction]; [thirdLevels release]; } [secondLevels release]; } [database commit]; [database release]; [firstLevels release];

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• What is the best way to iterate over a large result set in JDBC/iBatis 3?

  - by paul_sns

  We're trying to iterate over a large number of rows from the database and convert those into objects. Behavior will be as follows: Result will be sorted by sequence id, a new object will be created when sequence id changes. The object created will be sent to an external service and will sometimes have to wait before sending another one (which means the next set of data will not be immediately used) We already have invested code in iBatis 3 so an iBatis solution will be the best approach for us (we've tried using RowBounds but haven't seen how it does the iteration under the hood). We'd like to balance minimizing memory usage and reducing number of DB trips. We're also open to pure JDBC approach but we'd like the solution to work on different databases. UPDATE: We need to make as few calls to DB as possible (1 call would be the ideal scenario) while also preventing the application to use too much memory. Are there any other solutions out there for this type of problem may it be pure JDBC or any other technology? Thanks and hope to hear your insights on this.

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• Mixing RewriteRule and ProxyPass in Apache

  - by Taylor L

  I was working on debugging an issue today related to mixing mod_proxy and mod_rewrite together and I ended up having to use balancer://mycluster in the RewriteRule in order to stop receiving a 404 error from Apache. I have two questions: 1) Is there any other way to get the rewritten URL to go through the balancer without adding balancer://mycluster into the RewriteRule? 2) Is there a way to define all the parameters I defined in ProxyPass (stickysession=JSESSIONID|jsessionid scolonpathdelim=On lbmethod=bytraffic nofailover=Off) in either the <Proxy> or RewriteRule? I'm concerned the requests that match the new RewriteRule won't load balance in the same fashion as those that go through ProxyPass (like /app1/something.do)? Below are the relevant sections of the httpd.conf. I am using Apache 2.2. <Proxy balancer://mycluster> Order deny,allow Allow from all BalancerMember ajp://my.domain.com:8009 route=node1 BalancerMember ajp://my.domain.com:8009 route=node2 </Proxy> ProxyPass /app1 balancer://mycluster/app1 stickysession=JSESSIONID|jsessionid scolonpathdelim=On lbmethod=bytraffic nofailover=Off ProxyPassReverse /app1 ajp://my.domain.com:8009/app1 ... RewriteRule ^/static/cms/image/(.*)\.(.*) balancer://mycluster/app1/$1.$2 [P,L]

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• ASP.NET retrieve Average CPU Usage

  - by Sam

  Last night I did a load test on a site. I found that one of my shared caches is a bottleneck. I'm using a ReaderWriterLockSlim to control the updates of the data. Unfortunately at one point there are ~200 requests trying to update the data at approximately the same time. This also coincided with CPU usage spikes. The data being updated is in the ASP.NET Cache. What I'd like to do is if the CPU usage is around 75%, I'd like to just skip the cache and hit the database on another machine. My problem is that I don't know how expensive it is to create a new performance counter to check the cpu usage. Also, if I would probably like the average cpu usage over the last 2 or 3 seconds. However, I can't sit there and calculate the cpu time as that would take longer than it's taking to update the cache currently. Is there an easy way to get the average CPU usage? Are there any drawbacks to this? I'm also considering totaling the wait count for the lock and then at a certain threshold switch over to the database. The concern I had with this approach would be that changing hardware might allow more locks with less of a strain on the system. And also finding the right balance for the threshold would be cumbersome and it doesn't take into account any other load on the machine. But it's a simple approach, and simple is 99% of the time better.

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• SQL to CodeIgniter Array Missing Data Issue

  - by SamD

  $query = $this->db->query("SELECT t1.numberofbets, t1.profit, t2.seven_profit, t3.28profit, user.user_id, username, password, email, balance, user.date_added, activation_code, activated FROM user LEFT JOIN (SELECT user_id, SUM(amount_won) AS profit, count(tip_id) AS numberofbets FROM tip GROUP BY user_id) as t1 ON user.user_id = t1.user_id LEFT JOIN (SELECT user_id, SUM(amount_won) AS seven_profit FROM tip WHERE date_settled > '$seven_daystime' GROUP BY user_id) as t2 ON user.user_id = t2.user_id LEFT JOIN (SELECT user_id, SUM(amount_won) AS 28profit FROM tip WHERE date_settled > '$twoeight_daystime' GROUP BY user_id) as t3 ON user.user_id = t3.user_id where activated = 1 GROUP BY user.user_id ORDER BY user.date_added DESC"); return $query->result_array(); The query works fine running it in phpMyAdmin and returns complete results (in image attached). However, printing the array in CodeIgniter, it has no value for one field ,seven_profit, where it is there in the SQL query ran in phpMyAdmin, just the discrepancy in this one field, from sql to php array... I just can’t see why, when printing the array, that one field, which should have value of 26, contains nothing? Any ideas? I changed the field name from starting with a number in attempt to fix it, but no difference. I know this is complex and looks horrible, any help or just people coming across something similar would be great to know about, thanks. Sam

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• One big executable or many small DLL's?

  - by Patrick

  Over the years my application has grown from 1MB to 25MB and I expect it to grow further to 40, 50 MB. I don't use DLL's, but put everything in this one big executable. Having one big executable has certain advantages: Installing my application at the customer is really: copy and run. Upgrades can be easily zipped and sent to the customer There is no risk of having conflicting DLL's (where the customer has version X of the EXE, but version Y of the DLL) The big disadvantage of the big EXE is that linking times seem to grow exponentially. Additional problem is that a part of the code (let's say about 40%) is shared with another application. Again, the advantages are that: There is no risk on having a mix of incorrect DLL versions Every developer can make changes on the common code which speeds up developments. But again, this has a serious impact on compilation times (everyone compiles the common code again on his PC) and on linking times. The question http://stackoverflow.com/questions/2387908/grouping-dlls-for-use-in-executable mentions the possibility of mixing DLL's in one executable, but it looks like this still requires you to link all functions manually in your application (using LoadLibrary, GetProcAddress, ...). What is your opinion on executable sizes, the use of DLL's and the best 'balance' between easy deployment and easy/fast development?

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• In my cakephp project the save function is not working?

  - by Faheem

  My controller action is: function add() { if (!empty($this-data)) { $this-Customer-create(); if ($this-Customer-save($this-data)) { $this-Session-setFlash('A new Customer has been added'); $this-redirect(array('action'='index')); } else { $this-Session-setFlash('The customer cannot be added this time. Try again later.'); $this-redirect(array('action'='index')); } } } My model is: class Customer extends AppModel { var $name = 'Customer'; var $validate = array( 'name' = array( 'length'= array( 'rule' = array('between', 4,50), 'message' = 'Name must be minimum 4 and maximum 50 characters long.' ), 'checkUnique'= array( 'rule' = 'isUnique', 'message' = 'This Name is already registered' ) )); and this is my view: create('Customer',array('action'='add'));? input('Customer.name'); echo $form-input('Customer.balance',array('type'='hidden','default'=0)); ? end('Submit');? every time I submit the form it splashes: The customer cannot be added this time. Try again later.

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• Windows Azure - Automatic Load Balancing - partitioning

  - by veda

  I was going through some videos. I found that Windows Azure will group the blobs into partitions based on the partition key and will Automatically Load Balance these partitions on their servers. The partition key for a blob is blob name. Using the blob name, azure will automatically do partitions. Now, My question is that Can I able to make the azure to do partitions based on the Container Name. I wanted my partition key to be container name. For example, I have a storage account. In that I have 2 containers named container1 and container2. In container1, I have 1000 files named 1.txt, 2.txt, 3.txt, ......., 501.txt, 502.txt, ..... 999.txt, 1000.txt and in container2, I have another 1000 files named 1001.txt, 1002.txt, 1003.txt, ......., 1501.txt, 1502.txt, ..... 1999.txt, 2000.txt Now, Will Windows Azure will generate 2000 partitions based on the blob name and serve me through several servers??? Won't it be better if Azure partitions based on the Container name? container1 on one server and conatiner2 on another.

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• Latex multicols. Can I group content so it won't split over cols and/or suggest colbreaks?

  - by valadil

  Hi. I'm trying to learn LaTeX. I've been googling this one for a couple days, but I don't speak enough LaTeX to be able to search for it effectively and what documentation I have found is either too simple or goes way over my head (http://www.uoregon.edu/~dspivak/files/multicol.pdf) I have a document using the multicol package. (I'm actually using multicols* so that the first col fills before the second begins instead of trying to balance them, but I don't think that's relevant here.) The columns output nicely, but I want to be able to indicate that some content won't be broken up into different columns. For instance, aaaaaaaa bbbbbbb aaaaaaaa bbbbbbb aaaaaaaa ccccccc bbbbbbbb ccccccc That poor attempt at ascii art columns is what's happening. I'd like to indicate that the b block is a whole unit that shouldn't be broken up into different columns. Since it doesn't fit under the a block, the entirety of the b block should be moved to the second column. Should b be wrapped in something? Is there a block/float/section/box/minipage/paragraph structure I can use? Something specific to multicol? Alternatively is there a way that I can suggest a columnbreak? I'm thinking of something like \- that suggests a hyphenated line break if its convenient, but this would go between blocks. Thanks!

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• Advice Please: SQL Server Identity vs Unique Identifier keys when using Entity Framework

  - by c.batt

  I'm in the process of designing a fairly complex system. One of our primary concerns is supporting SQL Server peer-to-peer replication. The idea is to support several geographically separated nodes. A secondary concern has been using a modern ORM in the middle tier. Our first choice has always been Entity Framework, mainly because the developers like to work with it. (They love the LiNQ support.) So here's the problem: With peer-to-peer replication in mind, I settled on using uniqueidentifier with a default value of newsequentialid() for the primary key of every table. This seemed to provide a good balance between avoiding key collisions and reducing index fragmentation. However, it turns out that the current version of Entity Framework has a very strange limitation: if an entity's key column is a uniqueidentifier (GUID) then it cannot be configured to use the default value (newsequentialid()) provided by the database. The application layer must generate the GUID and populate the key value. So here's the debate: abandon Entity Framework and use another ORM: use NHibernate and give up LiNQ support use linq2sql and give up future support (not to mention get bound to SQL Server on DB) abandon GUIDs and go with another PK strategy devise a method to generate sequential GUIDs (COMBs?) at the application layer I'm leaning towards option 1 with linq2sql (my developers really like linq2[stuff]) and 3. That's mainly because I'm somewhat ignorant of alternate key strategies that support the replication scheme we're aiming for while also keeping things sane from a developer's perspective. Any insight or opinion would be greatly appreciated.

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• JSF Form is not showing up

  - by AnAmuser

  My server is glassfish v3, my browser is firefox 3.6.3 and i am using Netbeans 6.8 My question is why the textfield is not showing up in my browser. I only see the label. <?xml version='1.0' encoding='UTF-8' ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://java.sun.com/jsf/html" xmlns:f="http://java.sun.com/jsf/core"> <h:head> <title>Lookup</title> </h:head> <h:body> <fieldset> <legend>Enter Your Customer ID</legend> <p>Legal ids are id001, id002, and id003.</p> <f:view> <h:form> Customer ID: <h:inputText value="#{bankForm.customerId}" /> <h:commandButton value="Show Current Balance" action="#{bankForm.findBalance}" /> </h:form> </f:view> </fieldset> </h:body> </html>

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• Programming time schedule for porting a program.

  - by Lothar

  I'm working on a large program which has an abstracted GUI API. It is very GUI based, many dialogs and a few nasty features which rely heavily on the message flow of the GUI (correct sequences of focus/mouse/active handling etc.) - not easy to port I now want to port it from the currently used FOX Toolkit to native Cocoa/MFC. I give myself a timeframe until the end of the year but my main work will be to continue development work with the existing toolkit, but there is no planned release for end customers before both tasks are done. My question is how should i spend my time? Stop working on the main program and do a 90% port (about 3 month) of the GUI first Splitting everything into smaller sessions of one month each. Assigning Monday/Tuesday to the GUI project and the rest of the week for the app. Finishing the App first, then port. I think there are three arguments which i need to balance. Motivation, i want to see something going on on both projects Brain Input Overflow, both tasks require a lot of detail information in my brain and sometimes enough is just enough. I guess the porting is intervowen so porting would also require a lot of code changes in the existing code and the new code that will be written in the meantime.

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• Fluent NHibernate: Example of a one-to-many relationship on an abstract class of a table-per-subclas

  - by BigTommy79

  Hi All, I've been trying for ages to find an example (because I can't get it to work myself) of the correct mapping for a one-to-many relationship on an abstract class of a table-per-subclass implementation, in fluent nHibernate. An example below: I'm looking to map the list of Fines on the Debt abstract base class to the Fine class. if anyone knows of any tutorial or example they've come across before please let me know. Thanks, Tim public abstract class Entity { public int Id { get; set; } } public abstract class Debt : Entity { public decimal Balance { get; set; } public IList<Fine> Fines { get; set; } public Debt() { Fines = new List<Fine>(); } } public class CarLoan : Debt { } public class CreditCard : Debt { } public class LoanApplication : Entity { public IList<Debt> ExistingDebts { get; set; } public LoanApplication() { ExistingDebts = new List<Debt>(); } } public class Fine { public Int64 Cash { get; set; } }

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• OpenCV: Getting and Setting Camera Settings

  - by jhaip

  I have been searching around and can't find an example of how to get and set the camera capturing settings. For example the capturing resolution, fps, color balance, etc. I have only seen examples of how to change the settings when saving the captured video but I want to be able to find all the camera's capturing modes and choose which one I want. For example, I am using the PS3eye webcam and in the test program it allows you to change the settings (320x240 at 15,30,60,120 fps, 640x480 at 15,30,60,75 fps). So is there a function in OpenCV for getting all the camera's capture modes and choosing one? I remember in OpenFrameworks there was a function to change these settings but I would like to know how to do it in OpenCV. Here is the code for OpenFrameworks with OpenCV that does sort of what I want: vidGrabber.setDeviceID( 4 ); vidGrabber.setDesiredFrameRate( 30 ); //I want this vidGrabber.videoSettings(); vidGrabber.setVerbose(true); vidGrabber.initGrabber(320,240); //And this

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• Enterprise Platform in Python, Design Advice

  - by Jason Miesionczek

  I am starting the design of a somewhat large enterprise platform in Python, and was wondering if you guys can give me some advice as to how to organize the various components and which packages would help achieve the goals of scalability, maintainability, and reliability. The system is basically a service that collects data from various outside sources, with each outside source having its own separate application. These applications would poll a central database and get any requests that have been submitted to perform on the external source. There will be a main website and REST/SOAP API that should also have access to the central data service. My initial thought was to use Django for the web site, web service and data access layer (using its built-in ORM), and then the outside source applications can use the web service(s) to get the information they need to process the request and save the results. Using this method would allow me to have multiple instances of the service applications running on the same or different machines to balance out the load. Are there more elegant means of accomplishing this? i've heard of messaging systems such as MQ, would something like that be beneficial in this scenario? My other thought was to use a completely separate data service not based on Django, and use some kind of remoting or remote objects (in they exist in Python) to interact with the data model. The downside here would be with the website which would become much slower if it had to push all of its data requests through a second layer. I would love to hear what other developers have come up with to achieve these goals in the most flexible way possible.

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• Cannot Find Symbol Method?

  - by Aaron

  In my driver program, This line gives me cannot find symbol error and I don't know why, the method is clearly defined in the SavingsAccount class, and I can refer to all other methods in my driver program but just not that one, I tried changing the type to double, and etc but still not working. Refer to ** Account acct2 = new SavingsAccount (name); acct2.calculateBalance(); SavingsAccount Class Inherited from Account Class: public class SavingsAccount extends Account { private final short minBalance = 0; private double overdraftFee; private double yearlyInterestRate = 0.02; private double interestAmount; public SavingsAccount (String name) { super(name); } public double withdraw (double amount) { if (accountBalance - amount >= minBalance) { accountBalance -= amount; System.out.print ("Withdraw Successful"); } else { accountBalance -= amount; overdraftFee = accountBalance * (0.10); accountBalance += overdraftFee; System.out.print ("Withdraw Succesful, however overdraft fee of 10% has been applied to your account"); } return accountBalance; } **public void calculateBalance () { interestAmount = (accountBalance * yearlyInterestRate); accountBalance += interestAmount; }** public String toString() { return super.toString() + " Interest Received: " + interestAmount; } } Account class, if needed import java.util.Random; import java.text.NumberFormat; public abstract class Account { protected double accountBalance; protected long accountNumber; protected String accountHolder; public Account (String name) { accountHolder = name; accountBalance = 0; Random accountNo = new Random(); accountNumber = accountNo.nextInt(100000); } public double deposit (double amount) { accountBalance += amount; return accountBalance; } public String toString() { NumberFormat accountBal = NumberFormat.getCurrencyInstance(); return "Account Balance: " + accountBal.format(accountBalance) + "\nAccount Number: " + accountNumber; } public String getAccountHolder() { return accountHolder; } public double getAccountBalance() { return accountBalance; } public abstract double withdraw (double amount); }

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• What the heck is the "Structure and Interpretation of Computer Programs" cover drawing about?

  - by Paul Reiners

  What the heck is the Structure and Interpretation of Computer Programs cover drawing about? I mean I know what "eval", "apply", and '?' all mean, but I'm having a hard time deciphering the rest of the picture. Who the heck is the maiden? Does she work for the wizard? Why the heck is she pointing at the table? Is she pointing at that little bowl-type thing? Or the books? Or the table in general? Is she trying to tell the wizard that he should apply some sort of Lisp wizardry to the table or the items on it? Or is she just telling him something prosaic, such as his food is getting cold? What the heck is the one leg on that table that looks like...a leg...with a foot at the end (as legs tend to have)? How does the table balance on one leg? (Or is that another leg in the shadows?) [Note: I'm waiting for a lengthy build to finish in case you were wondering.]

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• Java Graphics not displaying on successive function calls, why?

  - by primehunter326

  Hi, I'm making a visualization for a BST implementation (I posted another question about it the other day). I've created a GUI which displays the viewing area and buttons. I've added code to the BST implementation to recursively traverse the tree, the function takes in coordinates along with the Graphics object which are initially passed in by the main GUI class. My idea was that I'd just have this function re-draw the tree after every update (add, delete, etc...), drawing a rectangle over everything first to "refresh" the viewing area. This also means I could alter the BST implementation (i.e by adding a balance operation) and it wouldn't affect the visualization. The issue I'm having is that the draw function only works the first time it is called, after that it doesn't display anything. I guess I don't fully understand how the Graphics object works since it doesn't behave the way I'd expect it to when getting passed/called from different functions. I know the getGraphics function has something to do with it. Relevant code: private void draw(){ Graphics g = vPanel.getGraphics(); tree.drawTree(g,ORIGIN,ORIGIN); } vPanel is what I'm drawing on private void drawTree(Graphics g, BinaryNode<AnyType> n, int x, int y){ if( n != null ){ drawTree(g, n.left, x-10,y+10 ); if(n.selected){ g.setColor(Color.blue); } else{ g.setColor(Color.gray); } g.fillOval(x,y,20,20); g.setColor(Color.black); g.drawString(n.element.toString(),x,y); drawTree(g,n.right, x+10,y+10); } } It is passed the root node when it is called by the public function. Do I have to have: Graphics g = vPanel.getGraphics(); ...within the drawTree function? This doesn't make sense!! Thanks for your help.

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• How to implement a grapher in C#

  - by iansinke

  So I'm writing a graphing calculator. So far I have a semi-functional grapher, however, I'm having a hard time getting a good balance between accurate graphs and smooth looking curves. The current implementation (semi-pseudo-code) looks something like this: for (float i = GraphXMin; i <= GraphXMax; i++) { PointF P = new PointF(i, EvaluateFunction(Function, i) ListOfPoints.Add(P) } Graphics.DrawCurve(ListOfPoints) The problem with this is since it only adds a point at every integer value, graphs end up distorted when their turning points don't fall on integers (e.g. sin(x)^2). I tried incrementing i by something smaller (like 0.1), which works, but the graph looks very rough. I am using C# and GDI+. I have SmoothingMethod set to AntiAlias, so that's not the problem, as you can see from the first graph. Is there some sort of issue with drawing curves with a lot of points? Should the points perhaps be positioned exactly on pixels? I'm sure some of you have worked on something very similar before, so any suggestions? While you're at it, do you have any suggestions for graphing functions with asymptotes? e.g. 1/x^2 P.S. I'm not looking for a library that does all this - I want to write it myself.

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• measure the response time of a link

  - by Ahoura Ghotbi

  I am trying to create a simple load balance script and I was wondering if it is possible to find the response time of a server live? By that I mean is it possible to measure how long it takes for a server to respond after the request has been sent out? What I am trying to do is fairly simple, I want to send a request to a link/server and do a count down, if the server took more than 5 seconds to reply, I would like to fall on the backup server. Note that it doesnt have to be in pure php, I wouldnt mind using other languages such as javascript, C/C++, asp, but I prefer to do it in PHP. if it is possible to do the task, could you just point me to the right direction so I can read up on it. Clarification What I want to do is not to download a file and see how long it took, my servers have high load and it takes a while for them to respond when you click on a file to download, what I want to do is to measure the time it takes the server to respond (in this situation, its the time it takes the server to respond and allow the user to download the file), and if it takes longer than x seconds, it should fall back on a backup server.

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• Is there a set based solution for this problem?

  - by NYSystemsAnalyst

  We have a table set up as follows: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|2.0 | |2 |2 |2/12/2010|Vacation Earned|3.0 | |3 |1 |2/4/2010 |Vacation Used |1.0 | |4 |2 |5/18/2010|Vacation Earned|2.0 | |5 |2 |7/23/2010|Vacation Used |4.0 | The business rules are: Vacation balance is calculated by vacation earned minus vacation used. Vacation used is always applied against the oldest vacation earned amount first. We need to return the rows for Vacation Earned that have not been offset by vacation used. If vacation used has only offset part of a vacation earned record, we need to return that record showing the difference. For example, using the above table, the result set would look like: |ID|EmployeeID|Date |Category |Hours| |1 |1 |1/1/2010 |Vacation Earned|1.0 | |4 |2 |5/18/2010|Vacation Earned|1.0 | Note that record 2 was eliminated because it was completely offset by used time, but records 1 and 4 were only partially used, so they were calculated and returned as such. The only way we have thought of to do this is to get all of the vacation earned records in a temporary table. Then, get the total vacation used and loop through the temporary table, deleting the oldest record and subtracting that value from the total vacation used until the total vacation used is zero. We could clean it up for when the remaining vacation used is only part of the oldest vacation earned record. This would leave us with just the outstanding vacation earned records. This works, but it is very inefficient and performs poorly. Also, the performance will just degrade over time as more and more records are added. Are there any suggestions for a better solution, preferable set based? If not, we'll just have to go with this.

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• What is the fastest (to access) struct-like object in Python?

  - by DNS

  I'm optimizing some code whose main bottleneck is running through and accessing a very large list of struct-like objects. Currently I'm using namedtuples, for readability. But some quick benchmarking using 'timeit' shows that this is really the wrong way to go where performance is a factor: Named tuple with a, b, c: >>> timeit("z = a.c", "from __main__ import a") 0.38655471766332994 Class using __slots__, with a, b, c: >>> timeit("z = b.c", "from __main__ import b") 0.14527461047146062 Dictionary with keys a, b, c: >>> timeit("z = c['c']", "from __main__ import c") 0.11588272541098377 Tuple with three values, using a constant key: >>> timeit("z = d[2]", "from __main__ import d") 0.11106188992948773 List with three values, using a constant key: >>> timeit("z = e[2]", "from __main__ import e") 0.086038238242508669 Tuple with three values, using a local key: >>> timeit("z = d[key]", "from __main__ import d, key") 0.11187358437882722 List with three values, using a local key: >>> timeit("z = e[key]", "from __main__ import e, key") 0.088604143037173344 First of all, is there anything about these little timeit tests that would render them invalid? I ran each several times, to make sure no random system event had thrown them off, and the results were almost identical. It would appear that dictionaries offer the best balance between performance and readability, with classes coming in second. This is unfortunate, since, for my purposes, I also need the object to be sequence-like; hence my choice of namedtuple. Lists are substantially faster, but constant keys are unmaintainable; I'd have to create a bunch of index-constants, i.e. KEY_1 = 1, KEY_2 = 2, etc. which is also not ideal. Am I stuck with these choices, or is there an alternative that I've missed?

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