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  • Design pattern: static function call with input/output containers?

    - by Pavlo Dyban
    I work for a company in software research department. We use algorithms from our real software and wrap them so that we can use them for prototyping. Every time an algorithm interface changes, we need to adapt our wrappers respectively. Recently all algorithms have been refactored in such a manner that instead of accepting many different inputs and returning outputs via referenced parameters, they now accept one input data container and one output data container (the latter is passed by reference). Algorithm interface is limited to a static function call like that: class MyAlgorithm{ static bool calculate(MyAlgorithmInput input, MyAlgorithmOutput &output); } This is actually a very powerful design, though I have never seen it in a C++ programming environment before. Changes in the number of parameters and their data types are now encapsulated and they don't change the algorithm callback. In the latest algorithm which I have developed I used the same scheme. Now I want to know if this is a popular design pattern and what it is called.

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  • Is the Leptonica implementation of 'Modified Median Cut' not using the median at all?

    - by TheCodeJunkie
    I'm playing around a bit with image processing and decided to read up on how color quantization worked and after a bit of reading I found the Modified Median Cut Quantization algorithm. I've been reading the code of the C implementation in Leptonica library and came across something I thought was a bit odd. Now I want to stress that I am far from an expert in this area, not am I a math-head, so I am predicting that this all comes down to me not understanding all of it and not that the implementation of the algorithm is wrong at all. The algorithm states that the vbox should be split along the lagest axis and that it should be split using the following logic The largest axis is divided by locating the bin with the median pixel (by population), selecting the longer side, and dividing in the center of that side. We could have simply put the bin with the median pixel in the shorter side, but in the early stages of subdivision, this tends to put low density clusters (that are not considered in the subdivision) in the same vbox as part of a high density cluster that will outvote it in median vbox color, even with future median-based subdivisions. The algorithm used here is particularly important in early subdivisions, and 3is useful for giving visible but low population color clusters their own vbox. This has little effect on the subdivision of high density clusters, which ultimately will have roughly equal population in their vboxes. For the sake of the argument, let's assume that we have a vbox that we are in the process of splitting and that the red axis is the largest. In the Leptonica algorithm, on line 01297, the code appears to do the following Iterate over all the possible green and blue variations of the red color For each iteration it adds to the total number of pixels (population) it's found along the red axis For each red color it sum up the population of the current red and the previous ones, thus storing an accumulated value, for each red note: when I say 'red' I mean each point along the axis that is covered by the iteration, the actual color may not be red but contains a certain amount of red So for the sake of illustration, assume we have 9 "bins" along the red axis and that they have the following populations 4 8 20 16 1 9 12 8 8 After the iteration of all red bins, the partialsum array will contain the following count for the bins mentioned above 4 12 32 48 49 58 70 78 86 And total would have a value of 86 Once that's done it's time to perform the actual median cut and for the red axis this is performed on line 01346 It iterates over bins and check they accumulated sum. And here's the part that throws me of from the description of the algorithm. It looks for the first bin that has a value that is greater than total/2 Wouldn't total/2 mean that it is looking for a bin that has a value that is greater than the average value and not the median ? The median for the above bins would be 49 The use of 43 or 49 could potentially have a huge impact on how the boxes are split, even though the algorithm then proceeds by moving to the center of the larger side of where the matched value was.. Another thing that puzzles me a bit is that the paper specified that the bin with the median value should be located, but does not mention how to proceed if there are an even number of bins.. the median would be the result of (a+b)/2 and it's not guaranteed that any of the bins contains that population count. So this is what makes me thing that there are some approximations going on that are negligible because of how the split actually takes part at the center of the larger side of the selected bin. Sorry if it got a bit long winded, but I wanted to be as thoroughas I could because it's been driving me nuts for a couple of days now ;)

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  • Optimizing processing and management of large Java data arrays

    - by mikera
    I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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  • Generic Event Generator and Handler from User Supplied Types?

    - by JaredBroad
    I'm trying to allow the user to supply custom data and manage the data with custom types. The user's algorithm will get time synchronized events pushed into the event handlers they define. I'm not sure if this is possible but here's the "proof of concept" code I'd like to build. It doesn't detect T in the for loop: "The type or namespace name 'T' could not be found" class Program { static void Main(string[] args) { Algorithm algo = new Algorithm(); Dictionary<Type, string[]> userDataSources = new Dictionary<Type, string[]>(); // "User" adding custom type and data source for algorithm to consume userDataSources.Add(typeof(Weather), new string[] { "temperature data1", "temperature data2" }); for (int i = 0; i < 2; i++) { foreach (Type T in userDataSources.Keys) { string line = userDataSources[typeof(T)][i]; //Iterate over CSV data.. var userObj = new T(line); algo.OnData < typeof(T) > (userObj); } } } //User's algorithm pattern. interface IAlgorithm<TData> where TData : class { void OnData<TData>(TData data); } //User's algorithm. class Algorithm : IAlgorithm<Weather> { //Handle Custom User Data public void OnData<Weather>(Weather data) { Console.WriteLine(data.date.ToString()); Console.ReadKey(); } } //Example "user" custom type. public class Weather { public DateTime date = new DateTime(); public double temperature = 0; public Weather(string line) { Console.WriteLine("Initializing weather object with: " + line); date = DateTime.Now; temperature = -1; } } }

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  • Cooperative linux vs vm

    - by Rhythmic Algorithm
    What are the advantages / disadvantages of using cooperative linux like portable ubuntu for example compared to a qemu or any other virtual machine installation. Is one option notably faster than the other plus and other things that should be taken into consideration.

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  • How to stop RAID5 array while it is shown to be busy?

    - by RCola
    I have a raid5 array and need to stop it, but while trying to stop it getting error. # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/2] [_UU] unused devices: <none> # mdadm --stop mdadm: metadata format 00.90 unknown, ignored. mdadm: metadata format 00.90 unknown, ignored. mdadm: No devices given. # mdadm --stop /dev/md0 mdadm: metadata format 00.90 unknown, ignored. mdadm: metadata format 00.90 unknown, ignored. mdadm: fail to stop array /dev/md0: Device or resource busy and # lsof | grep md0 md0_raid5 965 root cwd DIR 8,1 4096 2 / md0_raid5 965 root rtd DIR 8,1 4096 2 / md0_raid5 965 root txt unknown /proc/965/exe # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/2] [_UU] # grep md0 /proc/mdstat md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] # grep md0 /proc/partitions 9 0 2120320 md0 While booting, md1 is mounted ok but md0 failed for some unknown reason # dmesg | grep md[0-9] [ 4.399658] raid5: allocated 3179kB for md1 [ 4.400432] raid5: raid level 5 set md1 active with 3 out of 3 devices, algorithm 2 [ 4.400678] md1: detected capacity change from 0 to 2121793536 [ 4.403135] md1: unknown partition table [ 38.937932] Filesystem "md1": Disabling barriers, trial barrier write failed [ 38.941969] XFS mounting filesystem md1 [ 41.058808] Ending clean XFS mount for filesystem: md1 [ 46.325684] raid5: allocated 3179kB for md0 [ 46.327103] raid5: raid level 5 set md0 active with 2 out of 3 devices, algorithm 2 [ 46.330620] md0: detected capacity change from 0 to 2171207680 [ 46.335598] md0: unknown partition table [ 46.410195] md: recovery of RAID array md0 [ 117.970104] md: md0: recovery done. # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[0] sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/3] [UUU] md1 : active raid5 sdc2[0] sdf2[2] sde2[3](S) sdd2[1] 2072064 blocks level 5, 128k chunk, algorithm 2 [3/3] [UUU]

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  • How to get compatibility between C# and SQL2k8 AES Encryption?

    - by Victor Rodrigues
    I have an AES encryption being made on two columns: one of these columns is stored at a SQL Server 2000 database; the other is stored at a SQL Server 2008 database. As the first column's database (2000) doesn't have native functionality for encryption / decryption, we've decided to do the cryptography logic at application level, with .NET classes, for both. But as the second column's database (2008) allow this kind of functionality, we'd like to make the data migration using the database functions to be faster, since the data migration in SQL 2k is much smaller than this second and it will last more than 50 hours because of being made at application level. My problem started at this point: using the same key, I didn't achieve the same result when encrypting a value, neither the same result size. Below we have the full logic in both sides.. Of course I'm not showing the key, but everything else is the same: private byte[] RijndaelEncrypt(byte[] clearData, byte[] Key) { var memoryStream = new MemoryStream(); Rijndael algorithm = Rijndael.Create(); algorithm.Key = Key; algorithm.IV = InitializationVector; var criptoStream = new CryptoStream(memoryStream, algorithm.CreateEncryptor(), CryptoStreamMode.Write); criptoStream.Write(clearData, 0, clearData.Length); criptoStream.Close(); byte[] encryptedData = memoryStream.ToArray(); return encryptedData; } private byte[] RijndaelDecrypt(byte[] cipherData, byte[] Key) { var memoryStream = new MemoryStream(); Rijndael algorithm = Rijndael.Create(); algorithm.Key = Key; algorithm.IV = InitializationVector; var criptoStream = new CryptoStream(memoryStream, algorithm.CreateDecryptor(), CryptoStreamMode.Write); criptoStream.Write(cipherData, 0, cipherData.Length); criptoStream.Close(); byte[] decryptedData = memoryStream.ToArray(); return decryptedData; } This is the SQL Code sample: open symmetric key columnKey decryption by password = N'{pwd!!i_ll_not_show_it_here}' declare @enc varchar(max) set @enc = dbo.VarBinarytoBase64(EncryptByKey(Key_GUID('columnKey'), 'blablabla')) select LEN(@enc), @enc This varbinaryToBase64 is a tested sql function we use to convert varbinary to the same format we use to store strings in the .net application. The result in C# is: eg0wgTeR3noWYgvdmpzTKijkdtTsdvnvKzh+uhyN3Lo= The same result in SQL2k8 is: AI0zI7D77EmqgTQrdgMBHAEAAACyACXb+P3HvctA0yBduAuwPS4Ah3AB4Dbdj2KBGC1Dk4b8GEbtXs5fINzvusp8FRBknF15Br2xI1CqP0Qb/M4w I just didn't get yet what I'm doing wrong. Do you have any ideas? EDIT: One point I think is crucial: I have one Initialization Vector at my C# code, 16 bytes. This IV is not set at SQL symmetric key, could I do this? But even not filling the IV in C#, I get very different results, both in content and length.

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  • WPF Layout algorithm woes - control will resize, but not below some arbitrary value.

    - by Quantumplation
    I'm working on an application for a client, and one of the requirements is the ability to make appointments, and display the current week's appointments in a visual format, much like in Google Calender's or Microsoft Office. I found a great (3 part) article on codeproject, in which he builds a "RangePanel", and composes one for each "period" (for example, the work day.) You can find part 1 here: http://www.codeproject.com/KB/WPF/OutlookWpfCalendarPart1.aspx The code presents, but seems to choose an arbitrary height value overall (440.04), and won't resize below that without clipping. What I mean to say, is that the window/container will resize, but it just cuts off the bottom of the control, instead of recalculating the height of the range panels, and the controls in the range panels representing the appointment. It will resize and recalculate for greater values, but not less. Code-wise, what's happening is that when you resize below that value, first the "MeasureOverride" is called with the correct "new height". However, by the time the "ArrangeOverride" method is called, it's passing the same 440.04 value as the height to arrange to. I need to find a solution/workaround, but any information that you can provide that might direct me for things to look into would also be greatly appreciated ( I understand how frustrating it is to debug code when you don't have the codebase in front of you. :) ) The code for the various Arrange and Measure functions are provided below. The "CalendarView" control has a "CalendarViewContentPresenter", which handles several periods. Then, the periods have a "CalendarPeriodContentPresenter", which handles each "block" of appointments. Finally, the "RangePanel" has it's own implementation. (To be honest, i'm still a bit hazy on how the control works, so if my explanations are a bit hazy, the article I linked probably has a more cogent explanation. :) ) CalendarViewContentPresenter: protected override Size ArrangeOverride(Size finalSize) { int columnCount = this.CalendarView.Periods.Count; Size columnSize = new Size(finalSize.Width / columnCount, finalSize.Height); double elementX = 0; foreach (UIElement element in this.visualChildren) { element.Arrange(new Rect(new Point(elementX, 0), columnSize)); elementX = elementX + columnSize.Width; } return finalSize; } protected override Size MeasureOverride(Size constraint) { this.GenerateVisualChildren(); this.GenerateListViewItemVisuals(); // If it's coming back infinity, just return some value. if (constraint.Width == Double.PositiveInfinity) constraint.Width = 10; if (constraint.Height == Double.PositiveInfinity) constraint.Height = 10; return constraint; } CalendarViewPeriodPersenter: protected override Size ArrangeOverride(Size finalSize) { foreach (UIElement element in this.visualChildren) { element.Arrange(new Rect(new Point(0, 0), finalSize)); } return finalSize; } protected override Size MeasureOverride(Size constraint) { this.GenerateVisualChildren(); return constraint; } RangePanel: protected override Size ArrangeOverride(Size finalSize) { double containerRange = (this.Maximum - this.Minimum); foreach (UIElement element in this.Children) { double begin = (double)element.GetValue(RangePanel.BeginProperty); double end = (double)element.GetValue(RangePanel.EndProperty); double elementRange = end - begin; Size size = new Size(); size.Width = (Orientation == Orientation.Vertical) ? finalSize.Width : elementRange / containerRange * finalSize.Width; size.Height = (Orientation == Orientation.Vertical) ? elementRange / containerRange * finalSize.Height : finalSize.Height; Point location = new Point(); location.X = (Orientation == Orientation.Vertical) ? 0 : (begin - this.Minimum) / containerRange * finalSize.Width; location.Y = (Orientation == Orientation.Vertical) ? (begin - this.Minimum) / containerRange * finalSize.Height : 0; element.Arrange(new Rect(location, size)); } return finalSize; } protected override Size MeasureOverride(Size availableSize) { foreach (UIElement element in this.Children) { element.Measure(availableSize); } // Constrain infinities if (availableSize.Width == double.PositiveInfinity) availableSize.Width = 10; if (availableSize.Height == double.PositiveInfinity) availableSize.Height = 10; return availableSize; }

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  • How do you solve the 15-puzzle with A-Star or Dijkstra's Algorithm?

    - by Sean
    I've read in one of my AI books that popular algorithms (A-Star, Dijkstra) for path-finding in simulation or games is also used to solve the well-known "15-puzzle". Can anyone give me some pointers on how I would reduce the 15-puzzle to a graph of nodes and edges so that I could apply one of these algorithms? If I were to treat each node in the graph as a game state then wouldn't that tree become quite large? Or is that just the way to do it?

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  • Which DHT algorithm to use (if I want to join two separate DHTs)?

    - by webdreamer
    I've been looking into some DHT systems, specially Pastry and Chord. I've read some concerns about Chord's reaction to churn, though I believe that won't be a problem for the task I have at hands. I'm implementing some sort of social network service that doesn't rely on any central servers for a course project. I need the DHT for the lookups. Now I don't know of all the servers in the network in the beginning. As I've stated, there's no main tracker server. It works this way: each client has three dedicated servers. The three servers have the profile of the client, and it's wall, it's personal info, replicated. I only get to know about other group of servers when the user adds a friend (inputing the client's address). So I would create two separate DHTs on the two groups of three servers and when they friend each other I would like to join the DHTs. I would like to this consistently. I haven't had a lot of time to get all that familiar with the protocols, so I would like to know which one is better if I want to join the two separate DHTs?

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  • If I write an algorithm to encrypt a file, are their tools available to break the encryption?

    - by Andrew
    I have an idea for encryption that I could program fairly easily to encrypt some local text file. Given that my approach is novel, and does not use any of the industry standard encryption techniques, would I be able to test the strength of my encryption using 'cracker' apps or suchlike? Or do all those tools rely on advanced knowledge of the encryption process (or intercepted 'keys'), meaning I'd have to build my own cracker for testing?

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  • Defining < for STL sort algorithm - operator overload, functor or standalone function?

    - by Andy
    I have a stl::list containing Widget class objects. They need to be sorted according to two members in the Widget class. For the sorting to work, I need to define a less-than comparator comparing two Widget objects. There seems to be a myriad of ways to do it. From what I can gather, one can either: a. Define a comparison operator overload in the class: bool Widget::operator< (const Widget &rhs) const b. Define a standalone function taking two Widgets: bool operator<(const Widget& lhs, const Widget& rhs); And then make the Widget class a friend of it: class Widget { // Various class definitions ... friend bool operator<(const Widget& lhs, const Widget& rhs); }; c. Define a functor and then include it as a parameter when calling the sort function: class Widget_Less : public binary_function<Widget, Widget, bool> { bool operator()(const Widget &lhs, const Widget& rhs) const; }; Does anybody know which method is better? In particular I am interested to know if I should do 1 or 2. I searched the book Effective STL by Scott Meyer but unfortunately it does not have anything to say about this. Thank you for your reply.

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  • What is jasper report's algorithm for using a data source?

    - by spderosso
    Hi, I have created my custom data source by implementing the interface JRDataSource. This interface looks like this: public interface JRDataSource { /** * Tries to position the cursor on the next element in the data source. * @return true if there is a next record, false otherwise * @throws JRException if any error occurs while trying to move to the next element */ public boolean next() throws JRException; /** * Gets the field value for the current position. * @return an object containing the field value. The object type must be the field object type. */ public Object getFieldValue(JRField jrField) throws JRException; } My question is the following: In what way does jasper report call this functions for obtaining the fields in the .jrxml. E.g: if( next() )){ call getFieldValue for every field present in the page header while( next() ){ call getFieldValue for every field present in detail part } call getFieldValue for every field present the footer } The previous is just an example, experimentally in fact I found out that it is actually not like that. So my question arised. Thanks!

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  • What is the best algorithm to locate a point in an image file?

    - by suugaku
    Hi all, I want to create a mark sheet recognizer. Here is the description: My system uses black and white color scheme. The mark sheet paper has a small black rectangle on each corner and an additional small black rectangle, to determine orientation, near one of the previous rectangles. The paper is scanned to yield an image (in bmp format for example). The first step is to locate these five references in image as eficient as possible. My rough idea is to trace row by row and from left to right for each row. It sounds very slow I think. Is there any better way to do that? Thank you in advance. regards, Suugaku

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  • How to specify the image scaling algorithm used by a WPF Image?

    - by mackenir
    Is there a way to specify how an image is scaled up in an Image element with LayoutTransform set to a ScaleTransform with integer values for ScaleX and ScaleY? I want to display the scaled image crisply (ie using 'nearest neighbour' scaling), with no blurring. (Imagine how you would want a bitmap editing program to behave when zooming in). I noticed the protected property VisualBitmapScalingMode on Image, so created a subclass of Image that sets this property to BitmapScalingMode.NearestNeighbor. However, this had no effect.

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  • What's a good algorithm for searching arrays N and M, in order to find elements in N that also exist

    - by GenTiradentes
    I have two arrays, N and M. they are both arbitrarily sized, though N is usually smaller than M. I want to find out what elements in N also exist in M, in the fastest way possible. To give you an example of one possible instance of the program, N is an array 12 units in size, and M is an array 1,000 units in size. I want to find which elements in N also exist in M. (There may not be any matches.) The more parallel the solution, the better. I used to use a hash map for this, but it's not quite as efficient as I'd like it to be. Typing this out, I just thought of running a binary search of M on sizeof(N) independent threads. (Using CUDA) I'll see how this works, though other suggestions are welcome.

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