# 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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### Group-wise deviations from means / centering with dplyr vs. data.table

I am trying in R to "center" a matrix (i.e. remove mean) group-wise (i.e. remove group means for each variable). Input is a matrix (including the grouping variable), and output is the same matrix, ...
1answer
31 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 ...
1answer
68 views

### Combine Matrix Columns JavaScript

I did this Codepen to combine all the columns from one matrix in JS. ...
1answer
63 views

### Extract numerics from matrix A with logical matrix B

I have a matrix A containing numeric values and a matrix B containing 0/1s: ...
2answers
61 views

### 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. ...
0answers
90 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. ...
2answers
151 views

### Simple implementation of nxn Dense Matrix in Java

So far this is what I have completed. Still working on these two methods boolean isIdentityMatrix(DenseMatrix matrix); boolean isInvertible(DenseMatrix matrix); Suggestions are appreciated. Thanks. ...
1answer
36 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 ...
1answer
354 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, ...
0answers
68 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 ...
2answers
142 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 ...
1answer
7k 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 ...
1answer
78 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 ...
0answers
588 views

### Codewars: N-dimensional Von Neumann Neighborhood in a matrix

Task: For creating this challenge on Codewars I need a very performant function that calculates Von Neumann Neighborhood in a N-dimensional array. This function will be called about 2000 times The ...
0answers
1k 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 ...
1answer
469 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 ...
1answer
1k views

### Print concentric rectangular patterns

I am solving interview questions from here. Problem : Print concentric rectangular pattern in a 2d matrix. The outermost rectangle is formed by A, then the next outermost is formed by A-1 and so on....
3answers
582 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 ...
2answers
170 views

### 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 ...
1answer
5k views

### 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. ...
2answers
1k views

### Class Matrix implementation

Following the 18.06 Linear algebra course, I was curious to reinvent the matrix class and basic functionality, like $PA=LU$ decomposition, Gauss elimination, finding inverse matrix etc. Any ...
7answers
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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 ...
1answer
250 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 ...
3answers
157 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 ...
2answers
364 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 ...
1answer
291 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) ...
1answer
119 views

### 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 ...
1answer
210 views

### 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: ...
3answers
3k 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 ...
1answer
157 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 ...
1answer
980 views

### 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 ...
3answers
1k 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 ...
2answers
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 ...
1answer
4k views

### 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 ...
1answer
178 views

### 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 ...
1answer
461 views

### 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 ...
2answers
86 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 $\Theta(mn)$...
0answers
42 views

### 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 ...
2answers
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 ...
0answers
75 views

### Perl gradient noise generator

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 ...
2answers
872 views

### HackerRank - Queens Attack II - Java

The problem definition can already be found here. Given a chess board with dimensions n × n (where n is up to 100000) and the (r, c) positions of various obstacles, how many squares can a queen at a ...
1answer
392 views

### Spiral filling an existing matrix in their respective positions in descending order efficiently

Question: Sort the boundary elements in descending order using any standard sorting technique and rearrange them in the matrix. Calculate the sum of the boundary elements. Display the original matrix,...
3answers
7k views

### Rotate an N × N matrix 90 degrees clockwise

Given the problem from "Cracking the coding interview" Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees ...
1answer
8k views

### 4×4 matrix multiplication

This is a simple C++ code with a function mult to multiply matrices. This can easily be generalized for any $n \times n$ matrix by replacing ...
1answer
48 views

### Create a matrix where if an element in an M×N matrix is 0, its entire row and column are set to 0

How is my implementation? Are there improvements I can make to the variable names or any edge cases I might have missed? ...
1answer
172 views

### Greedy adaptive dictionary (GAD) for supervised machine learning [closed]

For my project in machine learning supervised, I have to simplify a training-data and I have to use this technique at page 5 of the document. Pseudocode algorithm My code (numbers are the steps): <...
2answers
701 views

### Short square matrix class in C++ using an array

I'm a novice at C++ in comparison with other languages, so as an exercise I wrote a square Matrix class that doesn't use STL. ...
1answer
984 views

### Rotating a matrix in Java

Introduction This program is about rotating a matrix. For example, let the matrix be abcde fghij klmno pqrst Now, after rotating two steps clockwise we will ...
1answer
744 views

### Leetcode 54: Spiral Matrix

Problem statement Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order. For example, Given the following matrix: [   [ 1, 2, 3 ], ...
3answers
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### Multiplication of any two matrices using lists and for in loop

I've just started learning Python and after few lessons I grasped the idea of lists and loop and decided to create my first project. Objective: Calculate multiplication of any two matrices from user'...