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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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32 views

Find the longest line in 2D (MxM) array (vertical, horizontal, or diagonal)

Find the length of the longest line with given square (MxM) matrix. (vertical, horizontal, or diagonal allowed) (Length of the longest line = number of consecutive 1's) i.e.) input: ...
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0answers
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+50

Determinant using Gauss Elimination

We had a question in examination to compute determinant of general square matrix. Now I had made the normal program using Laplace Formula of determinant, ie, recursive solution. Now I was thinking of ...
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3answers
3k views

Python 3 function to rotate an image 90°

A coding challenge that rotates an image 90 degrees counterclockwise. The image is represented as an array matrix. I believe the time complexity is O(n2), but I'd like to know for sure, as well as any ...
3
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1answer
66 views

Custom matrix object in C++

I have been getting back into C++ today, after a few years of Python and R. I am completely rusty, but decided to create a matrix object to re-familiarise. In reality I wouldn't use this class, since ...
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1answer
55 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 ...
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1answer
240 views

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, ...
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1answer
21 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 ...
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1answer
57 views

Combine Matrix Columns JavaScript

I did this Codepen to combine all the columns from one matrix in JS. ...
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1answer
43 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: ...
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2answers
57 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. ...
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0answers
30 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. ...
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2answers
33 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. ...
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27 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 ...
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1answer
95 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, ...
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0answers
42 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 ...
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2answers
64 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 ...
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1answer
151 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 ...
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1answer
74 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 ...
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173 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 ...
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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 ...
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1answer
204 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 ...
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1answer
329 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....
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3answers
246 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 ...
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2answers
99 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 ...
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1answer
369 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. ...
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1answer
194 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 ...
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7answers
1k views

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 ...
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1answer
63 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 ...
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3answers
147 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 ...
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2answers
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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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1answer
93 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) ...
2
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1answer
94 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 ...
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1answer
63 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: ...
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3answers
198 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 ...
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1answer
65 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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1answer
327 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 ...
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3answers
258 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 ...
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2answers
413 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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1answer
1k 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 ...
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1answer
101 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 ...
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1answer
139 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 ...
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2answers
71 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)\$...
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0answers
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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 ...
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2answers
354 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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1answer
71 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 ...
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2answers
281 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 ...
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1answer
111 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,...
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3answers
1k 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 ...
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1answer
1k views

General nxn Matrix multiplication (also can be non-square)

This is a simple c++ code with a function mult to multiply matrices. This can easily be generalized for any nxn matrix by replacing 4 with any positive number ...
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1answer
47 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? ...