# Questions tagged [matrix]

In mathematics, a matrix (plural matrices) is a rectangular array of numbers, symbols, or expressions, arranged in rows and columns. The individual items in a matrix are called its elements or entries.

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### Combine Matrix Columns JavaScript

I did this Codepen to combine all the columns from one matrix in JS. ...
63 views

### Fast algorithm for any(M==2)

I want to find a quick way to see if a matrix M has at least one value that is, say, 2. In R, I would use any(M==2). However, this computes first ...
34 views

### Creating the design matrices for a canonical correlation analysis

I have this code to generate symmetric matrices for testing how the design of the canonical correlation analysis I am performing works out. This is a extension of this solution Each row of the matrix ...
3k views

### 'Zero out' a matrix using Python

Below is my code for an attempted solution to cracking the coding interview exercise 1.8 written in python 3.5. The problem statement is: Write an algorithm such that if an element in an MxN ...
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### Symmetric Square

I was given an assignment to ensure that a list was symmetric. I built it in a way that worked and it passed the tests. But I wanted to see if it could've been written more efficiently and still ...
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### Eigenvector calculation involving three matrices

Code performs well for small matrices, but gives memory error for large matrices of size 63000x93000, even when I am using server with memory of 64GB, space 100GB, swap 40GB. ...
113 views

### Dijkstra in JavaScript

I am writing the solution of Dijkstra's algorithm in JS. This is what has happened so far. I need to make it so that the choice of nodes is by recursion. Tell me how to do this better. ...
41 views

### Extended matrix generation

I am extending a matrix with some calculated values. This code runs very slowly. Is there a way to vectorize this with slice and ...
80 views

### CUDA kernel to compare matrix entries, weighted with a pattern

I wonder if it's possible to optimize this code in CUDA. Could I get any hints how to? Equivalent algorithm runs faster in Matlab for me, but there I'm doing matrix operations. Compution I'm not ...
3k views

### Compute spherical distance matrix from list of geographical coordinates

I've got a list of geographic coordinates ([lat, long]) and want to compute the corresponding matrix of distances. Distance shall be spherical distance in km. <...
608 views

### Determinant of a matrix of doubles

I have been working with some matrix functions and need the determinant. I have looked at several examples, but they all seem to use a hard coded size for the matrix, or calculate for a matrix of int, ...
268 views

### Demonstration of Find Vowel Square

Have the function VowelSquare(strArr) take the strArr parameter being passed which will be a 2D matrix of some arbitrary size filled with letters from the alphabet, and determine if a 2x2 square ...
80 views

### R Function to Generate Predictions from Ratings and Save Results

I am trying to generate predictions using the function below in combination with sapply. My actual datasets are very large, I am attempting to make 1.5 million predictions with this function and it is ...
9k views

### Calculating the determinant of a matrix

I wanted to do some exercise and came up with the idea of a good challenge (for my level of course). I tried to implement Laplace's algorithm for computing the determinant, recursively. ...
10k views

### Sum of diagonal elements in a matrix [closed]

The idea is to calculate sum of diagonals example [[1,2,3],[4,5,6],[7,8,9] the correct answer would be [1,5,9][3,5,7] = total 30 ...
764 views

### A Simple Interactive Program that Can Solve A Linear System of Equations

So I was just reading my algebra-precalculus textbook, and learned that matrices can be used to solve systems of equations. Since the whole process seemed so algorithmic, I wondered if I could ...
2k views

### MIPS Assembly Program to access elements in the 4x4 matrix, row or column-major oder

This MIPS Assembly program will make you access the elements in the 4x4 matrix in either row or column-major order i.e. accessing all elements row by row or column by column. Output is posted below ...
9k views

### Finding a zero crossing in a matrix

I am trying create an algorithm for finding the zero crossing (check that the signs of all the entries around the entry of interest are not the same) in a two dimensional matrix, as part of ...
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### Computing the sum of squared differences

About Data: 3D data (100x100x20). Computation/Formula and Method: I am trying to compute the sum of squared differences along rows, columns and angles for various time differences. ...
341 views

### The Last Lost Bubble Shooter - a Board game for children

In this game the pieces are trains and you move forward on the track (never backwards) in search of your goal. The players move based on a combination of resources (Soap and Water to make Bubbles) ...
994 views

### Calculate median of a matrix

I am solving interview questions from here. Problem : Given a N cross M matrix in which each row is sorted, find the overall median of the matrix. Assume N*M is odd. Note: No extra memory is ...
2k views

### Sparse matrix compressed sparse row (CSR) in Python 2.7

Brief introduction for CSR: The compressed sparse row (CSR) or compressed row storage (CRS) format represents a matrix M by three (one-dimensional) arrays, that respectively contain nonzero ...
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### Multivariate normal density using Woodbury matrix inversion lemma

I'm trying to speed up by multivariate normal density function by taking advantage of the fact that the covariance matrix is of the form A + U C U'. The inverse of such a matrix can be calculated ...
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### Math matrix, mainly for graphics

I wrote a matrix library to replace my old matrix library. I was using my old matrix library to do basic operations for 3D rendering but that library grew old and now I'm seeking to replace it. I'm ...
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### Gaussian Elimination with Pivots

I'm pretty new to python, and coding in general. For practice, I've written the following code, which uses Gaussian reduction to solve a system of linear equations. ...
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### Code to multiply matrices together

I've got a short algorithm used in my code to multiply two matrices and put them into a destination Matrix. I decided to use the temporary array t_elements, which ...
166 views

### Finding black cluster size distribution for square grid at different probabilities of black elements (averaged over a certain number of iterations)

Context: I had asked a related question on Stack Overflow. On receiving several helpful hints from the commentators there, I could successfully implement averaging of the size distribution over a ...
369 views

### Draw common tangents to two circles interactively in MATLAB

Requirement After a user draws two circles with their mouse successively, the program should draw all common tangents, if any, to them. Here is my implementation ...
602 views

### Matrix Diagonal Difference

Problem Given a square matrix of size N×N, calculate the absolute difference between the sums of its diagonals. Input Format The first line contains a single ...
449 views

### Matrix Multiplication Implementation in CUDA C++ API with and without shared memory

Here is my implementation of matrix multiplication using the CUDA C++ API. I tried to separate the source code into multiple files for easier maintenance and readability. matrix.hpp By creating ...
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### Project Euler Problem 11 in Rust: largest product of consecutive elements of 20x20 grid

Here is my solution to problem 11 on Project Euler. The goal was to find the largest product of any four numbers in consecutive line of any direction (vertical, horizontal, or diagonal). While my ...
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### Basic Matrix Class in C++

I've made a simple Matrix class to learn C++. It doesn't use Templates so it only works with int. I made it this way to really understand how to work with objects ...
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### Solution to 90 degree rotation of an NxN matrix

The idea is picked up from here and the following is my PHP implementation of it. As it mentions, 90 degree matrix rotation basically shifts columns into rows. For example: ...
788 views

### Matrix rotation

Continuing on my VB.NET quest, I came across this slightly more challenging problem. You are given a 2D matrix, a, of dimension $M$x$N$ and a positive integer $R$. You have to rotate the ...
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### Implementing Transpose

I'm implementing transpose in Haskell. -- transpose [[1,2,3],[4,5,6],[7,8,9]] -- [[1,4,7],[2,5,8],[3,6,9]] Please give it a ...
7k views

### Matrix calculator in C

How can I make the code look cleaner, and what can I do to reduce the number of lines I have written? This program calculates the addition, subtraction and multiplication of matrices as well as ...
1k views

### Transposing a 2D array

Would you have any suggestions for improvements for the code below? ...
2k views

### Find the longest path in a matrix where each step has entries that differ by 1

Given an N*N matrix that all numbers are distinct in it, the function should find the maximum length path (starting from any cell) such that all the cells along the path are in increasing order with a ...
345 views

### Get column of a matrix python with index operator

How can I refactor this code to generalize the argument parsing? I feel like this code can be better but I can't find a way. The usage syntax of the index operator is similar to the NumPy indexing ...
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### Type safe, easy to understand matrix multiplication

I always hated matrices (as they are taught in those linear algebra course books that I have browsed), because it's an obscure way of saying "a tuple of linear functions of same arity". It is very ...
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### Matrix implementation with Rank and Inverse calculation using Gaussian Elimination in Java

Disclaimer Some things that I must state: This is just for practice. I want to know the various algorithms in linear algebra in detail. I will not use this in a practical scenario. Except for ...
2k views

### Find total number of paths in a matrix of 0's and 1's

I am working on a program which states that: You are given a 2-D matrix with M rows and N columns.You are initially positioned at (0,0) which is the top-left cell in the array. You are allowed to ...
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### Generating a word bigram co-occurrence matrix

I have written a method which is designed to calculate the word co-occurrence matrix in a corpus, such that element(i,j) is the number of times that word i follows word j in the corpus. Here is my ...
94 views

### Rotating a matrix in ANSI C

I have this C program that rotates a character matrix. This is a straightforward rewrite of this Java implementation. Both versions do additional $\Theta(mn)$ preprocessing and require $\Theta(mn)$...
796 views

### Compute the XOR of all the elements in the upper left triangular of a square matrix

Given a dimension $D$. We generate a $D\times D$ matrix with elements that start from $0$. For example, if we're given a dimension $4$ this is what our matrix looks like:  \begin{bmatrix}...
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### Deriving incremental feature representations for bit flips

Given a boolean 3D matrix and a set of actions specifying bit flips at certain positions, a set of resulting matrices can be obtained, one matrix for each action, as if executing each bit flip ...
2k views

### Efficiency and techniques for Matrix class that inherits from Python's list

I have a class named Matrix, this class inherits from Python's list. The class currently can ...
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I'm working on 2-D top-down graphics engine, and need a way to simulate clouds. My idea was that I could create a layer comprised of a matrix of rectangles whose alpha value would be picked from a ...