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• Matrix multiplication - Scene Graphs

  - by bgarate

  I wrote a MatrixStack class in C# to use in a SceneGraph. So, to get the world matrix for an object I am suposed to use: WorldMatrix = ParentWorld * LocalTransform But, in fact, it only works as expected when I do the other way: WorldMatrix = LocalTransform * ParentWorld Mi code is: public class MatrixStack { Stack<Matrix> stack =…

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• Find the "largest" dense sub matrix in a large sparse matrix

  - by BCS

  Given a large sparse matrix (say 10k+ by 1M+) I need to find a subset, not necessarily continuous, of the rows and columns that form a dense matrix (all non-zero elements). I want this sub matrix to be as large as possible (not the largest sum, but the largest number of elements) within some aspect ratio constraints. Are there any known exact or…

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• XNA matrix order problem

  - by user1990950

  I want a matrix that scales first and then rotates. I tried the code below, but it didn't work. zRotation, yRotation and xRotation are rotations that shouldn't be affected by the origin. allrot should be affected. xScale, yScale and zScale are the scaling variables. The code below works except that it rotates and then scales. Matrix worldMatrix…

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• Correct Rotation and Translation with a 4x4 matrix

  - by sFuller

  I am using a 4x4 matrix to transform verts in a shader. I multiply an identity matrix by a rotation matrix by a translation matrix. I am trying to first rotate the verts and then translate them, however in my result, it appears that the verts are being transformed and then rotated. My matrix looks something like this: m00 m01 m02 tx m10 m11 m12…

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• Faster Matrix Multiplication in C#

  - by Kyle Lahnakoski

  I have as small c# project that involves matrices. I am processing large amounts of data by splitting it into n-length chunks, treating the chucks as vectors, and multiplying by a Vandermonde** matrix. The problem is, depending on the conditions, the size of the chucks and corresponding Vandermonde** matrix can vary. I have a general solution…

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• Repeated Squaring - Matrix Multiplication using NEWMAT

  - by Dinakar Kulkarni

  I'm trying to use the repeated squaring algorithm (using recursion) to perform matrix exponentiation. I've included header files from the NEWMAT library instead of using arrays. The original matrix has elements in the range (-5,5), all numbers being of type float. # include "C:\User\newmat10\newmat.h" # include "C:\User\newmat10\newmatio.h" #…

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• OpenGL - Calculating camera view matrix

  - by Karle

  Problem I am calculating the model, view and projection matrices independently to be used in my shader as follows: gl_Position = projection * view * model * vec4(in_Position, 1.0); When I try to calculate my camera's view matrix the Z axis is flipped and my camera seems like it is looking backwards. My program is written in C# using the…

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• Xna Equivalent of Viewport.Unproject in a draw call as a matrix transformation

  - by Nick Crowther

  I am making a 2D sidescroller and I would like to draw my sprite to world space instead of client space so I do not have to lock it to the center of the screen and when the camera stops the sprite will walk off screen instead of being stuck at the center. In order to do this I wanted to make a transformation matrix that goes in my draw call.…

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• Inverting matrix then decomposing gives different quaternion than decomposing then inverting the quat

  - by Fraser

  I'm getting different signs when I convert a matrix to quaternion and invert that, versus when I invert a matrix and then get the quaternion from it: Quaternion a = Quaternion.Invert(getRotation(m)); Quaternion b = getRotation(Matrix.Invert(m)); I would expect a and b to be identical (or inverses of each other). However, it looks like q1…

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• matrix 4x4 position data

  - by freefallr

  I understand that a 4x4 matrix holds rotation and position data. The rotation data is held in the 3x3 sub-matrix at the top left of the matrix. The position data is held in the last column of the matrix. e.g. glm::vec3 vParentPos( mParent[3][0], mParent[3][1], mParent[3][2] ); My question is - am I accessing the…

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• C++ templates - matrix class

  - by lastOfMohicans

  Hi I'm learning templates in C++ so I decied to write matrix class which would be a template class. In Matrix.h file I wrote #pragma once #include "stdafx.h" #include <vector> using namespace std; template<class T> class Matrix { public: Matrix(); ~Matrix(); GetDataVector(); …

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• Matrix rotation wrong orientation LibGDX

  - by glz

  I'm having a problem with matrix rotation in libgdx. I rotate it using the method matrix.rotate(Vector3 axis, float angle) but the rotation happens in the model orientation and I need it happens in the world orientation. For example: on create() method: matrix.rotate(new Vector3(0,0,1), 45); That is ok, but…

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• Converting 3 axis vectors to a rotation matrix

  - by user38858

  I am trying to get a rotation matrix (in 3dsmax) from 3 vectors that form an axis (all 3 vectors are aligned by 90 degrees each other) Somewhere I read that I could build a rotation matrix just by inserting in every row one vector at a time (source:…

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• What is the best algorithm for solving a band-diagonal matrix?

  - by Goose Bumper

  I'm trying to figure out the best way to solve a pentadiagonal matrix. Is there something faster than gaussian elimination?

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• In R, when using named rows, can a sparse matrix column be added to another sparse matrix?

  - by ayman

  I have two sparse matrices, m1 and m2: > m1 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("b","d"),NULL)) > m2 <- Matrix(data=0,nrow=2, ncol=1, sparse=TRUE, dimnames=list(c("a","b"),NULL)) > m1["b",1]<- 4 >…

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• XNA Sprite Rotation Matrix - Moving Origin

  - by Jon

  I am currently grouping sprites together, then applying a rotation transformation on draw: private void UpdateMatrix(ref Vector2 origin, float radians) { Vector3 matrixorigin = new Vector3(origin, 0); _rotationMatrix =…

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• How can I generate a view or projection matrix for OpenGL 3.+

  - by Ken

  I'm transitioning from OpenGL 2 to OpenGL 3.+ and to GLSL 1.5. I'm trying to avoid using the deprecated features. My question how do we now generate the view or projection matrix. I was using the matrix stack to calculate the…

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• Matrix addition in Scheme

  - by user285012

  I am trying to add a matrix and it is not working... (define (matrix-matrix-add a b) (map (lambda (row) (row-matrix-add row b)) a)) (define (row-matrix-add row matrix) (if (null? (car matrix)) '() …

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• Need to translate a Rotation Matrix to Rotation y, x, z OpenGL & Jitter for 3D Game

  - by MineMan287

  I am using the Jitter Physics engine which gives a rotation matrix: M11 M12 M13 M21 M22 M23 M21 M32 M33 And I need it so OpenGL can use it for rotation GL.Rotate(xr, 1, 0, 0) GL.Rotate(yr, 0, 1, 0) GL.Rotate(zr, 0, 0,…

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• Is it possible to billboard a sprite using a transformation matrix?

  - by Ross

  None of the current topics on billboarding seemed to answer this question. But, given a sprite (or quad) that has it's own 4x4 transformation matrix a camera with a view matrix (a standard 4x4 transformation matrix) …

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• Matrix rotation of a rectangle to "face" a given point in 2d

  - by justin.m.chase

  Suppose you have a rectangle centered at point (0, 0) and now I want to rotate it such that it is facing the point (100, 100), how would I do this purely with matrix math? To give some more specifics I am using…

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• View matrix question (rotate by 180 degrees)

  - by King Snail

  I am using a third party rendering API on top of OpenGL code and I cannot get my matrices correct. The API states this: We're right handed by default, and we treat y as up by convention. Since IwGx's…

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• Getting the MODELVIEW matrix...

  - by james.ingham

  Hi, I've been pulling my hair out trying to get some matrix calculations working properly and started to wonder. If I have the following: glPushMatrix(); float m[16]; glGetFloatv(GL_MODELVIEW_MATRIX,…

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• Use a vector to index a matrix without linear index

  - by David_G

  G'day, I'm trying to find a way to use a vector of [x,y] points to index from a large matrix in MATLAB. Usually, I would convert the subscript points to the linear index of the matrix.(for eg. Use a…

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• Faster method for Matrix vector product for large matrix in C or C++ for use in GMRES

  - by user35959

  I have a large, dense matrix A, and I aim to find the solution to the linear system Ax=b using an iterative method (in MATLAB was the plan using its built in GMRES). For more than 10,000 rows, this…

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