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  • Memory read/write access efficiency

    - by wolfPack88
    I've heard conflicting information from different sources, and I'm not really sure which one to believe. As such, I'll post what I understand and ask for corrections. Let's say I want to use a 2D matrix. There are three ways that I can do this (at least that I know of). 1: int i; char **matrix; matrix = malloc(50 * sizeof(char *)); for(i = 0; i < 50; i++) matrix[i] = malloc(50); 2: int i; int rowSize = 50; int pointerSize = 50 * sizeof(char *); int dataSize = 50 * 50; char **matrix; matrix = malloc(dataSize + pointerSize); char *pData = matrix + pointerSize - rowSize; for(i = 0; i < 50; i++) { pData += rowSize; matrix[i] = pData; } 3: //instead of accessing matrix[i][j] here, we would access matrix[i * 50 + j] char *matrix = malloc(50 * 50); In terms of memory usage, my understanding is that 3 is the most efficient, 2 is next, and 1 is least efficient, for the reasons below: 3: There is only one pointer and one allocation, and therefore, minimal overhead. 2: Once again, there is only one allocation, but there are now 51 pointers. This means there is 50 * sizeof(char *) more overhead. 1: There are 51 allocations and 51 pointers, causing the most overhead of all options. In terms of performance, once again my understanding is that 3 is the most efficient, 2 is next, and 1 is least efficient. Reasons being: 3: Only one memory access is needed. We will have to do a multiplication and an addition as opposed to two additions (as in the case of a pointer to a pointer), but memory access is slow enough that this doesn't matter. 2: We need two memory accesses; once to get a char *, and then to the appropriate char. Only two additions are performed here (once to get to the correct char * pointer from the original memory location, and once to get to the correct char variable from wherever the char * points to), so multiplication (which is slower than addition) is not required. However, on modern CPUs, multiplication is faster than memory access, so this point is moot. 1: Same issues as 2, but now the memory isn't contiguous. This causes cache misses and extra page table lookups, making it the least efficient of the lot. First and foremost: Is this correct? Second: Is there an option 4 that I am missing that would be even more efficient?

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  • iPhone OpenGL ES - How to Pick

    - by Ali Nadalizadeh
    I'm working on an OpenGL ES1 app which displays a 2D grid and allows user to navigate and scale/rotate it. I need to know the exact translation of View Touch coordinates into my opengl world and grid cell. Are there any helpers to do the reverse of last few transforms which I do for navigation ? or I should calculate and do the matrix stuff by hand ?

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  • Matrices of "long"s in Java/COLT?

    - by Darren Wilkinson
    I'm very new to Java/COLT so apologies if this is a dumb question... But, is it possible to define (2d) matrices of type "long" using the cern.colt.matrix stuff? If so, how?! I can find an abstract class for "Object" and a concrete implementation for "double", but then I am stuck... Thanks,

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  • Any ideas on How to search a 2D array quickly?

    - by Tattat
    I jave a 2D array like this, just like a matrix: {{1, 2, 4, 5, 3, 6}, {8, 3, 4, 4, 5, 2}, {8, 3, 4, 2, 6, 2}, //code skips... ... } I want to get all the "4" position, instead of searching the array one by way, and return the position, how can I search it faster / more efficient? thz in advance.

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  • java double[][] - display as image

    - by joe_shmoe
    Hi all, just wondering if there is a simple way in java to display the contents of say 16x16 array of doubles [0..1] as a greyscale image (ala matlab)? using an unfamiliar matrix library, so I'd like to check that I'm on the right track. don't really care if it is slow or ugly, or if it requires external library - it's just there for a quick look, so as long as it works, I'm fine.

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  • Graph representation

    - by Carlucho
    Given graph, how could i represent it using adj matrix?. I have read lots of tutorials, post, slides, etc but i cant get my head round it, i just need that little push.

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  • How do you rotate a two dimensional array?

    - by swilliams
    Inspired by Raymond Chen's post, say you have a 4x4 two dimensional array, write a function that rotates it 90 degrees. Raymond links to a solution in pseudo code, but I'd like to see some real world stuff. [1][2][3][4] [5][6][7][8] [9][0][1][2] [3][4][5][6] Becomes: [3][9][5][1] [4][0][6][2] [5][1][7][3] [6][2][8][4] Update: Nick's answer is the most straightforward, but is there a way to do it better than n^2? What if the matrix was 10000x10000?

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  • XNA model drawing problem

    - by user1990950
    When using this code: public static void DrawModel(Model model, Vector3 position, Vector3 offset, float xRotation, float yRotation, float zRotation, float allrot, float xScale, float yScale, float zScale) { position.Y *= -1; offset.Y *= -1; Matrix worldMatrix = ((Matrix.CreateRotationZ(MathHelper.ToRadians(zRotation)) * Matrix.CreateRotationX(MathHelper.ToRadians(xRotation))) * Matrix.CreateRotationY(MathHelper.ToRadians(yRotation))) * (Matrix.CreateTranslation(offset) * Matrix.CreateRotationY(MathHelper.ToRadians(allrot))) * Matrix.CreateScale(xScale, yScale, zScale); worldMatrix *= Matrix.CreateTranslation(position) * theCamera.GetTransformation() * Matrix.CreateTranslation(new Vector3(-(graphics.GraphicsDevice.Viewport.Width / 2), graphics.GraphicsDevice.Viewport.Height / 2, 0)); foreach (ModelMesh mesh in model.Meshes) { for (int i = 0; i < mesh.Effects.Count; i++) { ((BasicEffect)mesh.Effects[i]).EnableDefaultLighting(); ((BasicEffect)mesh.Effects[i]).World = worldMatrix; ((BasicEffect)mesh.Effects[i]).View = viewMatrix; ((BasicEffect)mesh.Effects[i]).Projection = projectionMatrix; } mesh.Draw(); } } The model rotates and then scales. It should scale and then rotate, but whenever I try to change it, it won't work.

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  • How do I go about overloading C++ operators to allow for chaining?

    - by fneep
    I, like so many programmers before me, am tearing my hair out writing the right-of-passage-matrix-class-in-C++. I have never done very serious operator overloading and this is causing issues. Essentially, by stepping through This is what I call to cause the problems. cMatrix Kev = CT::cMatrix::GetUnitMatrix(4, true); Kev *= 4.0f; cMatrix Baz = Kev; Kev = Kev+Baz; //HERE! What seems to be happening according to the debugger is that Kev and Baz are added but then the value is lost and when it comes to reassigning to Kev, the memory is just its default dodgy values. How do I overload my operators to allow for this statement? My (stripped down) code is below. //header class cMatrix { private: float* _internal; UInt32 _r; UInt32 _c; bool _zeroindexed; //fast, assumes zero index, no safety checks float cMatrix::_getelement(UInt32 r, UInt32 c) { return _internal[(r*this->_c)+c]; } void cMatrix::_setelement(UInt32 r, UInt32 c, float Value) { _internal[(r*this->_c)+c] = Value; } public: cMatrix(UInt32 r, UInt32 c, bool IsZeroIndexed); cMatrix( cMatrix& m); ~cMatrix(void); //operators cMatrix& operator + (cMatrix m); cMatrix& operator += (cMatrix m); cMatrix& operator = (const cMatrix &m); }; //stripped source file cMatrix::cMatrix(cMatrix& m) { _r = m._r; _c = m._c; _zeroindexed = m._zeroindexed; _internal = new float[_r*_c]; UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] = m._internal[i]; } } cMatrix::~cMatrix(void) { delete[] _internal; } cMatrix& cMatrix::operator+(cMatrix m) { return cMatrix(*this) += m; } cMatrix& cMatrix::operator*(float f) { return cMatrix(*this) *= f; } cMatrix& cMatrix::operator*=(float f) { UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] *= f; } return *this; } cMatrix& cMatrix::operator+=(cMatrix m) { if (_c != m._c || _r != m._r) { throw new cCTException("Cannot add two matrix classes of different sizes."); } if (!(_zeroindexed && m._zeroindexed)) { throw new cCTException("Zero-Indexed mismatch."); } for (UInt32 row = 0; row < _r; row++) { for (UInt32 column = 0; column < _c; column++) { float Current = _getelement(row, column) + m._getelement(row, column); _setelement(row, column, Current); } } return *this; } cMatrix& cMatrix::operator=(const cMatrix &m) { if (this != &m) { _r = m._r; _c = m._c; _zeroindexed = m._zeroindexed; delete[] _internal; _internal = new float[_r*_c]; UInt32 size = GetElementCount(); for (UInt32 i = 0; i < size; i++) { _internal[i] = m._internal[i]; } } return *this; }

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  • Converting a WPFToolkit DataGrid from 1D list to 2D matrix

    - by user61073
    Hello - I am wondering if anyone has attempted the following or has an idea as to how to do it. I have a WPFToolkit DataGrid which is bound to an ObservableCollection of items. As such, the DataGrid is shown with as many rows in the ObservableCollection, and as many columns as I have defined in for the DataGrid. That all is good. What I now need is to provide another view of the same data, only, instead, the DataGrid is shown with as many cells in the ObservableCollection. So let's say, my ObservableCollection has 100 items in it. The original scenario showed the DataGrid with 100 rows and 1 column. In the modified scenario, I need to show it with 10 rows and 10 columns, where each cell shows the value that was in the original representation. In other words, I need to transform my 1D ObservableCollection to a 2D ObservableCollection and display it in the DataGrid. I know how to do that programmatically in the code behind, but can it be done in XAML? Let me simplify the problem a little, in case anybody can have a crack at this. The XAML below does the following: * Defines an XmlDataProvider just for dummy data * Creates a DataGrid with 10 columns o each column is a DataGridTemplateColumn using the same CellTemplate * The CellTemplate is a simple TextBlock bound to an XML element If you run the XAML below, you will find that the DataGrid ends up with 5 rows, one for each book, and 10 columns that have identical content (all showing the book titles). However, what I am trying to accomplish, albeit with a different data set, is that in this case, I would end up with one row, with each book title appearing in a single cell in row 1, occupying cells 0-4, and nothing in cells 5-9. Then, if I added more data and had 12 books in my XML data source, I would get row 1 completely filled (cells covering the first 10 titles) and row 2 would get the first 2 cells filled. Can my scenario be accomplished primarily in XAML, or should I resign myself to working in the code behind? Any guidance would greatly be appreciated. Thanks so much! <UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:custom="http://schemas.microsoft.com/wpf/2008/toolkit" mc:Ignorable="d" x:Name="UserControl" d:DesignWidth="600" d:DesignHeight="400" > <UserControl.Resources> <XmlDataProvider x:Key="InventoryData" XPath="Inventory/Books"> <x:XData> <Inventory xmlns=""> <Books> <Book ISBN="0-7356-0562-9" Stock="in" Number="9"> <Title>XML in Action</Title> <Summary>XML Web Technology</Summary> </Book> <Book ISBN="0-7356-1370-2" Stock="in" Number="8"> <Title>Programming Microsoft Windows With C#</Title> <Summary>C# Programming using the .NET Framework</Summary> </Book> <Book ISBN="0-7356-1288-9" Stock="out" Number="7"> <Title>Inside C#</Title> <Summary>C# Language Programming</Summary> </Book> <Book ISBN="0-7356-1377-X" Stock="in" Number="5"> <Title>Introducing Microsoft .NET</Title> <Summary>Overview of .NET Technology</Summary> </Book> <Book ISBN="0-7356-1448-2" Stock="out" Number="4"> <Title>Microsoft C# Language Specifications</Title> <Summary>The C# language definition</Summary> </Book> </Books> <CDs> <CD Stock="in" Number="3"> <Title>Classical Collection</Title> <Summary>Classical Music</Summary> </CD> <CD Stock="out" Number="9"> <Title>Jazz Collection</Title> <Summary>Jazz Music</Summary> </CD> </CDs> </Inventory> </x:XData> </XmlDataProvider> <DataTemplate x:Key="GridCellTemplate"> <TextBlock> <TextBlock.Text> <Binding XPath="Title"/> </TextBlock.Text> </TextBlock> </DataTemplate> </UserControl.Resources> <Grid x:Name="LayoutRoot"> <custom:DataGrid HorizontalAlignment="Stretch" VerticalAlignment="Stretch" IsSynchronizedWithCurrentItem="True" Background="{DynamicResource WindowBackgroundBrush}" HeadersVisibility="All" RowDetailsVisibilityMode="Collapsed" SelectionUnit="CellOrRowHeader" CanUserResizeRows="False" GridLinesVisibility="None" RowHeaderWidth="35" AutoGenerateColumns="False" CanUserReorderColumns="False" CanUserSortColumns="False"> <custom:DataGrid.Columns> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="01" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="02" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="03" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="04" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="05" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="06" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="07" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="08" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="09" /> <custom:DataGridTemplateColumn CellTemplate="{StaticResource GridCellTemplate}" Header="10" /> </custom:DataGrid.Columns> <custom:DataGrid.ItemsSource> <Binding Source="{StaticResource InventoryData}" XPath="Book"/> </custom:DataGrid.ItemsSource> </custom:DataGrid> </Grid>

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  • MATLAB using MAT2CELL

    - by Ali
    i have the following matrices letter=[A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ... a b c d e f g h ii jj k l m o p q r s t u v w x y z]; number=[one two three four five six seven eight nine zero]; character =[number letter]; Character becomes a matrix of 42 by 1464, but i would like to break it into cells of 42 by 24 using mat2cell. How can i please do it, every time i try i get an error????

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  • How to get predecessor and successors from an adjacency matrix

    - by NickTFried
    Hi I am am trying to complete an assignment, where it is ok to consult the online community. I have to create a graph class that ultimately can do Breadth First Search and Depth First Search. I have been able to implement those algorithms successfully however another requirement is to be able to get the successors and predecessors and detect if two vertices are either predecessors or successors for each other. I'm having trouble thinking of a way to do this. I will post my code below, if anyone has any suggestions it would be greatly appreciated. import java.util.ArrayList; import java.util.Iterator; import java.util.LinkedList; import java.util.Queue; import java.util.Stack; public class Graph<T> { public Vertex<T> root; public ArrayList<Vertex<T>> vertices=new ArrayList<Vertex<T>>(); public int[][] adjMatrix; int size; private ArrayList<Vertex<T>> dfsArrList; private ArrayList<Vertex<T>> bfsArrList; public void setRootVertex(Vertex<T> n) { this.root=n; } public Vertex<T> getRootVertex() { return this.root; } public void addVertex(Vertex<T> n) { vertices.add(n); } public void removeVertex(int loc){ vertices.remove(loc); } public void addEdge(Vertex<T> start,Vertex<T> end) { if(adjMatrix==null) { size=vertices.size(); adjMatrix=new int[size][size]; } int startIndex=vertices.indexOf(start); int endIndex=vertices.indexOf(end); adjMatrix[startIndex][endIndex]=1; adjMatrix[endIndex][startIndex]=1; } public void removeEdge(Vertex<T> v1, Vertex<T> v2){ int startIndex=vertices.indexOf(v1); int endIndex=vertices.indexOf(v2); adjMatrix[startIndex][endIndex]=1; adjMatrix[endIndex][startIndex]=1; } public int countVertices(){ int ver = vertices.size(); return ver; } /* public boolean isPredecessor( Vertex<T> a, Vertex<T> b){ for() return true; }*/ /* public boolean isSuccessor( Vertex<T> a, Vertex<T> b){ for() return true; }*/ public void getSuccessors(Vertex<T> v1){ } public void getPredessors(Vertex<T> v1){ } private Vertex<T> getUnvisitedChildNode(Vertex<T> n) { int index=vertices.indexOf(n); int j=0; while(j<size) { if(adjMatrix[index][j]==1 && vertices.get(j).visited==false) { return vertices.get(j); } j++; } return null; } public Iterator<Vertex<T>> bfs() { Queue<Vertex<T>> q=new LinkedList<Vertex<T>>(); q.add(this.root); printVertex(this.root); root.visited=true; while(!q.isEmpty()) { Vertex<T> n=q.remove(); Vertex<T> child=null; while((child=getUnvisitedChildNode(n))!=null) { child.visited=true; bfsArrList.add(child); q.add(child); } } clearVertices(); return bfsArrList.iterator(); } public Iterator<Vertex<T>> dfs() { Stack<Vertex<T>> s=new Stack<Vertex<T>>(); s.push(this.root); root.visited=true; printVertex(root); while(!s.isEmpty()) { Vertex<T> n=s.peek(); Vertex<T> child=getUnvisitedChildNode(n); if(child!=null) { child.visited=true; dfsArrList.add(child); s.push(child); } else { s.pop(); } } clearVertices(); return dfsArrList.iterator(); } private void clearVertices() { int i=0; while(i<size) { Vertex<T> n=vertices.get(i); n.visited=false; i++; } } private void printVertex(Vertex<T> n) { System.out.print(n.label+" "); } }

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  • Is Matlab faster than Python?

    - by kame
    I want to compute magnetic fields of some conductors using the biot-savart-law and I want to use a 1000x1000x1000 matrix. Before I use Matlab, but now I want to use Python. Is Python slower than Matlab? How can I make Python faster? EDIT: Maybe the best way is to compute the big array with c/c++ and then transfering them to python. I want to visualise then with VPython. EDIT2: Could somebody give an advice for which is better in my case: C or C++?

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  • More complex view matrix calculation required to composite 3d models with 2d video

    - by lzcd
    I'm utilising some 2d / 3d tracking data (provided by pfHoe) to help integrate some 3d models into the playback of some 2d video. Things are working.... okay... but there's still some visible 'slipping' of the models against the video background and I suspect this is may be because the XNA CreatePerspective helper method isn't taking into account some of the additional data supplied by pfHoe such as independent horizontal / vertical field of view angles and focal length. Would anyone be able to point me towards some examples of constructing view matrices that include such details?

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  • MATLAB (MATrix LABoratory) interview questions?

    - by Shane
    I programmed in Matlab for many years, but switched to using R exclusively in the past few years so I'm a little out of practice. I'm interviewing a candidate today who describes himself as a Matlab expert. What MATLAB interview questions that I should be asking?

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  • How to use Eclipse and versioning for a matrix of projects

    - by Nulldevice
    Our company develop several software products, which reuse each others packages (we use Java). Every product represented as separate Eclipse Java project and has it's own versioning repository (we use Mercurial). When we find a bug in some shared package, we need to transfer changes to all consuming projects, and this is a hell. The key problem is that Eclipse project can be associated only with one versioning repository. Could someone recommend some way to associate Eclipse Java project whith several versioning repositories which in ideal may be geterogeious (svn, git, mercurial) ?

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  • How to set orthgraphic matrix for a 2d camera with zooming?

    - by MahanGM
    I'm using ID3DXSprite to draw my sprites and haven't set any kind of camera projection matrix. How to setup an orthographic projection matrix for camera in DirectX which it would be able to support zoom functionality? D3DXMATRIX orthographicMatrix; D3DXMATRIX identityMatrix; D3DXMatrixOrthoLH(&orthographicMatrix, nScreenWidth, nScreenHeight, 0.0f, 1.0f); D3DXMatrixIdentity(&identityMatrix); device->SetTransform(D3DTS_PROJECTION, &orthographicMatrix); device->SetTransform(D3DTS_WORLD, &identityMatrix); device->SetTransform(D3DTS_VIEW, &identityMatrix); This code is for initial setup. Then, for zooming I multiply zoom factor in nScreenWidth and nScreenHeight.

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  • Operating on rows and then on columns of a matrix produces code duplication

    - by Chetan
    I have the following (Python) code to check if there are any rows or columns that contain the same value: # Test rows -> # Check each row for a win for i in range(self.height): # For each row ... firstValue = None # Initialize first value placeholder for j in range(self.width): # For each value in the row if (j == 0): # If it's the first value ... firstValue = b[i][j] # Remember it else: # Otherwise ... if b[i][j] != firstValue: # If this is not the same as the first value ... firstValue = None # Reset first value break # Stop checking this row, there's no win here if (firstValue != None): # If first value has been set # First value placeholder now holds the winning player's code return firstValue # Return it # Test columns -> # Check each column for a win for i in range(self.width): # For each column ... firstValue = None # Initialize first value placeholder for j in range(self.height): # For each value in the column if (j == 0): # If it's the first value ... firstValue = b[j][i] # Remember it else: # Otherwise ... if b[j][i] != firstValue: # If this is not the same as the first value ... firstValue = None # Reset first value break # Stop checking this column, there's no win here if (firstValue != None): # If first value has been set # First value placeholder now holds the winning player's code return firstValue # Return it Clearly, there is a lot of code duplication here. How do I refactor this code? Thanks!

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