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• Why wouldn't `new int[x]{}` be valid???

  - by dboarman-FissureStudios

  In MonoDevelop I have the following code which compiles: int[] row = new int[indices.Count]{}; However, at run-time, I get: Matrix.cs(53,53): Error CS0150: A constant value is expected (CS0150) (testMatrix) I know what this error means and forces me to then resize the array: int[] row = new int[indices.Count]{}; Array.Resize(ref row, rowWidth); Is this something I just have to deal with because I am using MonoDevelop on Linux? I was certain that under .Net 3.5 I was able to initialize an array with a variable containing the width of the array. Can anyone confirm that this is isolated? If so, I can report the bug to bugzilla.

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• How to share a variable between two classes?

  - by Altefquatre

  How would you share the same object between two other objects? For instance, I'd like something in that flavor: class A { private string foo_; // It could be any other class/struct too (Vector3, Matrix...) public A (string shared) { this.foo_ = shared; } public void Bar() { this.foo_ = "changed"; } } ... // inside main string str = "test"; A a = new A(str); Console.WriteLine(str); // "test" a.Bar(); Console.WriteLine(str); // I get "test" instead of "changed"... :( I read there is some ref/out stuff, but I couldn't get what I'm asking here. I could only apply some changes in the methods scope where I was using ref/out arguments... I also read we could use pointers, but is there no other way to do it?

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• Which machine learning library to use

  - by Space_C0wb0y

  I am looking for a library that, ideally, has the following features: implements hierarchical clustering of multidimensional data (ideally on similiarity or distance matrix) implements support vector machines is in C++ is somewhat documented (this one seems to be hardest) I would like this to be in C++, as I am most comfortable with that language, but I will also use any other language if the library is worth it. I have googled and found some, but I do not really have the time to try them all out, so I want hear what other people had for experiences. Please only answer if you have some experience with the library you recommend. P.S.: I could also use different libraries for the clustering and the SVM.

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• MATLAB submatrix over variable dimensions

  - by rlbond

  I have a variable dimension matrix, X. I want a function that will get the first half of X in one dimension. I.E., I want something like this: function x = variableSubmatrix(x, d) if d == 1 switch ndims(x) case 1 x = x(1:end/2); case 2 x = x(1:end/2, :); case 3 x = x(1:end/2, :, :); (...) end elseif d == 2 switch ndims(x) case 2 x = x(:, 1:end/2); case 3 x = x(:, 1:end/2, :); (...) end elseif (...) end end I'm not quite sure how to do this. I need it to be fast, as this will be used many times in computation.

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• Why might different computers calculate different arithmetic results in VB.NET?

  - by Eyal

  I have some software written in VB.NET that performs a lot of calculations, mostly extracting jpegs to bitmaps and computing calculations on the pixels like convolutions and matrix multiplication. Different computers are giving me different results despite having identical inputs. What might be the reason? Edit: I can't provide the algorithm because it's proprietary but I can provide all the relevant operations: ULong \ ULong (Turuncating division) Bitmap.Load("filename.bmp') (Load a bitmap into memory) Bitmap.GetPixel(Integer, Integer) (Get a pixel's brightness) Double + Double Double * Double Math.Sqrt(Double) Math.PI Math.Cos(Double) ULong - ULong ULong * ULong ULong << ULong List.OrderBy(Of Double)(Func) Hmm... Is it possible that OrderBy is using a non-stable QuickSort and that QuickSort is using a random pivot? Edit: Just tested, nope. The sort is stable.

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• Crystal Report with mutliple row columns.

  - by Jack

  I'm not sure if the title properly explains what I'm trying to do. I'm trying to move from using SQL Reporting Services to a Crystal Reports Web App. I've gotten some reports to design properly because they are simple cross-tab reports that require nothing special. I'm running into a little problem of a user matrix report. Here's how the report looks on SQL Reporting Services: group1 group2 group3 username1 first1 last1 title1 X X username2 first2 last2 title2 X X 2 1 1 Normally in VS2008 with a SQL rdl, I would right click on the row and Insert Column. However, i don't see a way to do this in Crystal Reports. I've tried setting up multiple row groups, but that adds mutliple groupings like: group1 Total ... Username Total ... first Total ... last ...

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• How do I draw an ellipse with arbitrary orientation pixel by pixel?

  - by amc

  Hi, I have to draw an ellipse of arbitrary size and orientation pixel by pixel. It seems pretty easy to draw an ellipse whose major and minor axes align with the x and y axes, but rotating the ellipse by an arbitrary angle seems trickier. Initially I though it might work to draw the unrotated ellipse and apply a rotation matrix to each point, but it seems as though that could cause errors do to rounding, and I need rather high precision. Is my suspicion about this method correct? How could I accomplish this task more precisely? I'm programming in C++ (although that shouldn't really matter since this is a more algorithm-oriented question).

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• Opinions on collision detection objects with a moving scene

  - by Evan Teran

  So my question is simple, and I guess it boils down to how anal you want to be about collision detection. To keep things simple, lets assume we're talking about 2D sprites defined by a bounding box. In addition, let's assume that my sprite object has a function to detect collisions like this: S.collidesWith(other); Finally the scene is moving and "walls" in the scene can move, an object may not touch a wall. So a simple implementation might look like this (psuedo code): moveWalls(); moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } The problem with this is that if the sprite and wall move towards each other, depending on the circumstances (such as diagonal moment). They may pass though each other (unlikely but could happen). So I may do this instead. moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } This takes care of the passing through each other issue, but another rare issue comes up. If they are adjacent to each other (literally the next pixel) and both the wall and the sprite are moving left, then I will get an invalid collision since the wall moves, checks for collision (hit) then the sprite is moved. Which seems unfair. In addition, to that, the redundant collision detection feels very inefficient. I could give the player movement priority alleviating the first issue but it is still checking twice. moveSprite(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } moveWalls(); foreach(wall as w) { if(s.collidesWith(w)) { gameover(); } } Am I simply over thinking this issue, should this just be chalked up to "it'll happen rare enough that no one will care"? Certainly looking at old sprite based games, I often find situations where the collision detection has subtle flaws, but I figure by now we can do better :-P. What are people's thoughts?

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• Scale GraphicsPaths

  - by serhio

  In a form I draw a graph. This graph has some distinct paths that should have differently drawn. Say AxesPath, SalesPath, CostsPath etc... When I resize the form need I to scale every of components Paths? Take an example: Imports System.Drawing.Drawing2D Public Class Form1 Dim lineOne As GraphicsPath Dim lineTwo As GraphicsPath Dim allPaths As GraphicsPath Dim initSize As Size Public Sub New() ' This call is required by the designer. ' InitializeComponent() initSize = Me.Size lineOne = New GraphicsPath() lineTwo = New GraphicsPath() lineOne.AddLine(20.0F, 20.0F, Me.initSize.Width - 20.0F, 20.0F) lineTwo.AddLine(0.1F, 10.0F, Me.initSize.Width - 20.0F, _ Me.initSize.Height - 0.5F) allPaths = New GraphicsPath() allPaths.AddPath(lineOne, False) allPaths.AddPath(lineTwo, False) Me.ResizeRedraw = True End Sub Protected Overrides Sub OnResize(ByVal e As System.EventArgs) MyBase.OnResize(e) Dim m As New Matrix m.Scale(Me.Width / initSize.Width, Me.Height / initSize.Height) allPaths.Transform(m) initSize = Me.Size End Sub Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) MyBase.OnPaint(e) ' WORKS ' ' e.Graphics.DrawPath(Pens.GreenYellow, allPaths) ' ' DOES NOT WORK! ' e.Graphics.DrawPath(Pens.DarkGoldenrod, lineOne) e.Graphics.DrawPath(Pens.DarkMagenta, lineTwo) End Sub End Class

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• best method of turning millions of x,y,z positions of particles into visualisation

  - by Griff

  I'm interested in different algorithms people use to visualise millions of particles in a box. I know you can use Cloud-In-Cell, adaptive mesh, Kernel smoothing, nearest grid point methods etc to reduce the load in memory but there is very little documentation on how to do these things online. i.e. I have array with: x,y,z 1,2,3 4,5,6 6,7,8 xi,yi,zi for i = 100 million for example. I don't want a package like Mayavi/Paraview to do it, I want to code this myself then load the decomposed matrix into Mayavi (rather than on-the-fly rendering) My poor 8Gb Macbook explodes if I try and use the particle positions. Any tutorials would be appreciated.

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• Python - Using "Google AJAX Search" API's Local Search Objects

  - by user330739

  Hi! I've just started using Google's search API to find addresses and the distances between those addresses. I used geopy for this, but, I often had the problem of not getting the correct addresses for my queries. I decided to experiment, therefore, with Google's "Local Search" (http://code.google.com/apis/ajaxsearch/local.html). Anyway, I wanted to ask if I could use the "Local Search" objects provided by the API within python. Something tells me that I can't and that I have to use json. Does anyone know if there is a work around? PS: Im trying to make something like this: http://www.google.com/uds/samples/random/lead.html ... except a matrix type deal where the insides will be filled with distances between the addresses. Thanks for reading!

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• C++ MTL Library dimension.h bug?

  - by avanwieringen

  I've installed MTL on my Fedora Core 12 x64 system, but when building an application I get the following error: In file included from /usr/local/include/mtl/matrix.h:41, from /usr/local/include/mtl/mtl.h:40, from ltiSystem.hxx:4, from strTools.hxx:4, from ff.cxx:3: /usr/local/include/mtl/envelope2D.h:72: error: declaration of ‘typedef struct mtl::twod_tag mtl::envelope2D<T>::dimension’ /usr/local/include/mtl/dimension.h:19: error: changes meaning of ‘dimension’ from ‘class mtl::dimension<typename mtl::dense1D<T, 0>::size_type, 0, 0>’ make[1]: *** [ff.o] Error 1 Which would imply an error in MTL. I have changed to different MTL versions and the problem persists, but on Google there is no proper answer. I use the g++ compiler. Does anyone have a clye?

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• invalid conversion from 'char' to 'int* in C

  - by majdal

  Hi, I have the following arrays: int A[] = {0,1,1,1,1, 1,0,1,0,0, 0,1,1,1,1}; int B[] = {1,1,1,1,1, 1,0,1,0,1, 0,1,0,1,0}; int C[] = {0,1,1,1,0, 1,0,0,0,1, 1,0,0,0,1}; //etc... for all letters of the alphabet And a function that prints the letters on a 5x3 LED matrix: void printLetter(int letter[]) I have a string of letters: char word[] = "STACKOVERFLOW"; and I want to pass each character of the string to the printLetter function. I tried: int n = sizeof(word); for (int i = 0; i < n-1; i++) { printLetter(word[i]); } But I get the following error: invalid conversion from 'char' to 'int*' What should i be doing? Thanks!!

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• Java: Preventing array going out of bounds.

  - by Troy

  I'm working on a game of checkers, if you want to read more about you can view it here; http://minnie.tuhs.org/I2P/Assessment/assig2.html When I am doing my test to see if the player is able to get to a certain square on the grid (i.e. +1 +1, +1 -1 .etc) from it's current location, I get an java.lang.ArrayIndexOutOfBoundsException error. This is the code I am using to make the move; public static String makeMove(String move, int playerNumber) { // variables to contain the starting and destination coordinates, subtracting 1 to match array size int colStart = move.charAt(1) - FIRSTCOLREF - 1; int rowStart = move.charAt(0) - FIRSTROWREF - 1; int colEnd = move.charAt(4) - FIRSTCOLREF - 1; int rowEnd = move.charAt(3) - FIRSTROWREF - 1; // variable to contain which player is which char player, enemy; if (playerNumber==1) { player= WHITEPIECE; enemy= BLACKPIECE; } else { player= BLACKPIECE; enemy= WHITEPIECE; } // check that the starting square contains a player piece if (grid [ colStart ] [ rowStart ] == player) { // check that the player is making a diagonal move if (grid [ colEnd ] [ rowEnd ] == grid [ (colStart++) ] [ (rowEnd++) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart--) ] [ (rowEnd++) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart++) ] [ (rowEnd--) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart--) ] [ (rowEnd--) ]) { // check that the destination square is free if (grid [ colEnd ] [ rowEnd ] == BLANK) { grid [ colStart ] [ rowStart ] = BLANK; grid [ colEnd ] [ rowEnd ] = player; } } // check if player is jumping over a piece else if (grid [ colEnd ] [ rowEnd ] == grid [ (colStart+2) ] [ (rowEnd+2) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart-2) ] [ (rowEnd+2) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart+2) ] [ (rowEnd-2) ] && grid [ colEnd ] [ rowEnd ] == grid [ (colStart-2) ] [ (rowEnd-2) ]) { // check that the piece in between contains an enemy if ((grid [ (colStart++) ] [ (rowEnd++) ] == enemy ) && (grid [ (colStart--) ] [ (rowEnd++) ] == enemy ) && (grid [ (colStart++) ] [ (rowEnd--) ] == enemy ) && (grid [ (colStart--) ] [ (rowEnd--) ] == enemy )) { // check that the destination is free if (grid [ colEnd ] [ rowEnd ] == BLANK) { grid [ colStart ] [ rowStart ] = BLANK; grid [ colEnd ] [ rowEnd ] = player; } } } } I'm not sure how I can prevent the error from happening, what do you recommend?

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• Finding many local max in an image (using MatLab)

  - by wenh42

  How do you go about figuring our multiple max in a 2D image where the max aren't necessarily all the same height? I have found that the imregionalmax(), imextendedmax(), and findpeaks() functions aren't necessarily that helpful because they give many local max that are really just maxes within the background noise. I tried bw=arrayimdilate(array,[1 1 1; 1 0 1; 1 1 1]) but that also is kind of limited for the same reasons (same thing with expanding the matrix that it uses). I'd definitely appreciate some help..

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• Testing for the existence of a field in a class

  - by Brett

  Hi, i have a quick question. I have a 2D array that stores an instance of a class. The elements of the array are assigned a particular class based on a text file that is read earlier in the program. Since i do not know without looking in the file what class is stored at a particular element i could refer to a field that doesn't exist at that index (referring to appearance when an instance of temp is stored in that index). i have come up with a method of testing this, but it is long winded and requires a second matrix. Is there a function to test for the existence of a field in a class? class temp(): name = "default" class temp1(): appearance = "@"

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• iphone: repeating a transformation

  - by gonso

  Hi I'm trying to represent a view that rotates on the iphone screen. I have a button and when you press it, the view rotates 180 degrees. My problem is that this only works the first time. Here is the code: -(IBAction) flip:(id)sender{ CGAffineTransform transform; //the transform matrix to be used below //BEGIN ANIMATIONS [UIView beginAnimations:nil context:NULL]; [UIView setAnimationDuration:2.0]; //animate if (flag){ transform = CGAffineTransformMakeRotation( RADIANS(180) ); } else { transform = CGAffineTransformMakeRotation( RADIANS(-180) ); } flag = !flag; transform = CGAffineTransformTranslate(transform, 0, 0); self.mySuview.transform = transform; //COMMIT ANIMATIONS [UIView commitAnimations]; } The first time you click, the view spins alright, but when you click again NOTHING happens. No errors, no changes on the view. What am I missing? Thanks Gonso

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• Recursion Interview Questions [closed]

  - by halivingston

  Given a string, "ABC", print all permutations Given a dollar bill, fill out possible ways it can summed up using .25, .10, .5, etc. Given a phone number (123-456), print out all it's word counter parters like (ADG-XYZ) A B C D E F G H I J K L M N O P In the above 2D matrix, print all possible words (just literally all words, and sure we could check if it's exists in a dictionary). The base case is I think here is that reaching the same i, j positions. Any others you can think of?

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• Preallocate memory for a program in Linux before it gets started

  - by Fyg

  Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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• Expert system for writing programs?

  - by aaa

  I am brainstorming an idea of developing a high level software to manipulate matrix algebra equations, tensor manipulations to be exact, to produce optimized C++ code using several criteria such as sizes of dimensions, available memory on the system, etc. Something which is similar in spirit to tensor contraction engine, TCE, but specifically oriented towards producing optimized rather than general code. The end result desired is software which is expert in producing parallel program in my domain. Does this sort of development fall on the category of expert systems? What other projects out there work in the same area of producing code given the constraints?

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• How to create a "dependency graph" for IT assets

  - by p.marino

  One of my customers is trying to create an interactive "matrix" of interdependencies for the various applications used in their company (it's a travel&leisure company with around 2500 employees). The idea (still at the prototype stage) is to create a sort of Map, based on Visio or similar tool, which traces the communication and interdependencies between all the IT assets in the company, so that when someone asks for a change they can get an overview of the impacts. This was mentioned in a casual setting and it will not be my responsability to directly work on this, but I did contribute the little I know already in terms of vaguely related methodologies (Zachman Framework). I'd like to hear from the people in here if they know of methodologies, or tools, that may help this kind of effort, and if they have any specific experience to contribute. I'll digest the answers and send the result back to my customer, hoping this may be of some help with their task (which I consider a bit visionary and prone to all the pitfalls of any documentation project, but still well worth pursuing).

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• Distributing a function over a single dimension of an array in MATLAB?

  - by Alex Feinman

  I often find myself wanting to collapse an n-dimensional matrix across one dimension, and can't figure out if there is a concise incantation I can use to do this. For example, when parsing an image, I often want to do something like this. (Note! Illustrative example only. I know about rgb2gray for this specific case.) img = imread('whatever.jpg'); s = size(img); for i=1:s(1) for j=1:s(2) bw_img = mean(img(i,j,:)); end end I would love to express this as something like: bw = on(color, 3, @mean); or bw(:,:,1) = mean(color); Is there a short way to do this?

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• Why do MSTests Assert.AreEqual(1.0, double.NaN, 0.0) pass?

  - by Egil Hansen

  Short question, why do Assert.AreEqual(1.0, double.NaN, 0.0) pass when Assert.AreEqual(1.0, double.NaN) do not? Is it an error in MSTest or am I missing something here? Best regards, Egil. Update: Should probably add, that the reason behind my question is, that I have a bunch of unit tests that unfortunately passed due to the result of some linear algebraic matrix operation being NaN or (+/-)Infinity. The unit tests are fine, but since Assert.AreEqual on doubles with a delta will pass when actual or/and expected are NaN or Infinity, I was left to believe that the code I was testing was correct.

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• OpenGL Performance Questions

  - by Daniel

  This subject, as with any optimisation problem, gets hit on a lot, but I just couldn't find what I (think) I want. A lot of tutorials, and even SO questions have similar tips; generally covering: Use GL face culling (the OpenGL function, not the scene logic) Only send 1 matrix to the GPU (projectionModelView combination), therefore decreasing the MVP calculations from per vertex to once per model (as it should be). Use interleaved Vertices Minimize as many GL calls as possible, batch where appropriate And possibly a few/many others. I am (for curiosity reasons) rendering 28 million triangles in my application using several vertex buffers. I have tried all the above techniques (to the best of my knowledge), and received almost no performance change. Whilst I am receiving around 40FPS in my implementation, which is by no means problematic, I am still curious as to where these optimisation 'tips' actually come into use? My CPU is idling around 20-50% during rendering, therefore I assume I am GPU bound for increasing performance. Note: I am looking into gDEBugger at the moment Cross posted at Game Development

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• C++ domain specific embedded language operators

  - by aaa

  hi. In numerical oriented languages (Matlab, Fortran) range operator and semantics is very handy when working with multidimensional data. For example: A(i:j,k,:n) // represents two-dimensional slice B(i:j,0:n) of A at index k unfortunately C++ does not have range operator (:). of course it can be emulated using range/slice functor, but semantics is less clean than Matlab. I am prototyping matrix/tensor domain language in C++ and am wondering if there any options to reproduce range operator. I still would like to rely on C++/prprocessor framework exclusively. So far I have looked through boost wave which might be an suitable option. is there any other means to introduce new operators to C++ DSL?

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