# 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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### stochastic gradient descent - backpropagation over mini-batches in one go

I have been working through a tutorial on neural networks (http://neuralnetworksanddeeplearning.com). I have then been translating the code to java, to help improve my understanding of what the code ...
9k views

### Rotate Matrix using Python

This is my solution to Exercise 1.7 from Cracking the Coding Interview. I would appreciate any feedback on coding style and algorithm efficiency. I do know that there is an existing function in ...
75 views

### Large matrix with lots of repetitive fields (C++)

I wrote a timetabling program and I have been using a matrix to check for clashes between courses. Index (i, j) in the matrix ...
8 views

### Construct sparse Smolyak index matrix in Matlab [on hold]

I need to construct a matrix defined by two variables. The first, d is the dimensions and the second, l, is the level. The matrix has as many columns as the value of d. The elements of the rows are ...
104 views

### Picking seats in a matrix

I'm trying to write a Python class that creates a matrix of zeros, then uses a random number generator to pick 'seats' on the matrix. It changes the zero in that seat to a one, until the matrix is all ...
61 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: ...
140 views

### Ruby implementation for Hacker Rank connected cells in a grid

https://www.hackerrank.com/challenges/connected-cell-in-a-grid/problem problem statement: Consider a matrix where each cell contains either a 1 or a 0. Any cell containing a 1 is called a ...
59 views

### 4×4 cofactor in SSE

The cofactor of a 4×4 matrix can be used to convert a "regular geometry" matrix into the matrix that transforms the normals. It's an alternative to the common inverse-transpose pattern. In this post I ...
171 views

### Creation of matrix with specific attempts at the end

What I want to do is build a Slay-the-Spire-like Map. As you can see in the following image, the map is splitted in ISteps and ...
73 views

### Find the number of pawns available for a rook to capture

I find that very very often with matrix questions, the traversal and comparison part of the solution is very verbose and repetitive. For example, this code (written for a coding challenge) to find ...
81 views

### Generate a large block diagonal covariance matrix with exponential decay

I am implementing Kalman filtering in R. Part of the problem involves generating a really huge error covariance block-diagonal matrix (dim: 18000 rows x 18000 columns = 324,000,000 entries). We denote ...
67 views

### Golang matrix package

I developed a small package to do matrix math. I just learned Go so I may have done it wrong. ...
132 views

### Modeling, view and projection transformation using vector and point in homogenous form

I know this is horrible code. This program is for performing modeling, view and projection transformation. The program reads input from scene.txt and outputs the <...
86 views

### Getting saddle points of a matrix

My homework assignment: Write a function called saddle that finds saddle points in the input matrix M. For the purposes of this problem, a saddle point is defined as an element whose value is ...
3k views

### Searching in a sorted 2D matrix

If I was at an interview, and wrote this code, what would you think? Please be brutal. Time it took to wrote it: 13 minutes Problem: Write an efficient algorithm that searches for a value in an m ...
75 views

### Pad a ragged multidimensional array to rectangular shape

For some machine learning purpose, I need to work with sequences with different lengths. To be able to process efficiently those sequences, I need to process them in batches of size ...
2k views

### Converting Data in Rows and Columns to Rows in VBA for Excel

I have a working VBA script for Excel that converts a matrix of data with multiple records in per row to multiple rows with one record per row. A StackOverflow user told me that the code could use ...
35 views

### Spiral printing elements of a matrix

As I'm learning elixir, I wrote some code for printing elements in the spiral of a matrix(2D array). I was wondering if there is any room for improvements with regards to its performance or ...
89 views

### Rotate matrix clockWise and counter clockWise

This code is a mix of the same question one time rotating to the right and one time to the left. I tried to simplify the code since I'm struggling with all of the indexing here. https://leetcode.com/...
51 views

### CUDA matrix class

I started to work on this CUDA C matrix class to learn both the object oriented programming in C++ and to learn CUDA. The initial goal of this project was to make a matrix class that can have almost ...
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### Generating random sparse matrix

My goal is to generate a large sparse matrix with majority (~99%) zeros and ones. Ideally, I would be working with 10,000 rows and 10,000,000 columns. Additionally, each column is generated as a ...
54 views

### LeetCode: Transpose Matrix C#

Please review performance https://leetcode.com/problems/transpose-matrix/ Given a matrix A, return the transpose of A. The transpose of a matrix is the matrix flipped over it's main ...
55 views

### Striping a matrix concentrically, anticlockwise

Given a matrix you shall stripe the matrix, such that every number that has equal distance to the matrix border will be filled into an array. For examples see code comments. ...
97 views

### Python program to solve matrix-chain multiplication

An assignment at school required me to write a Python program for this task: In the matrix-chain multiplication problem, we are given a sequence of matrices ...
52 views

### Matrix input in N*N form in Python

I am using the below code in Python to input a N*N matrix in its original form: ...
50 views

### Multiplying a Matrix with its Transpose

Currently, I am in the process of optimizing a MIPS assembly program that takes a n x n matrix and multiplies it with its transpose. I am trying to optimize my matrix calculation algorithm so that it ...
5k 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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### Transposing a square matrix (n x n)

I wish to transpose a square matrix, permanently overwriting it. This is not the same as creating a 2nd matrix with the transposed contents of the 1st matrix. I call the procedure with 3 parameters: ...
3k views

### 4x4 matrix implementation in C++

I've been doing some 3D graphics in OpenGL lately and I needed a way to work with 4x4 matrices. My implementation supports the following operations: Matrix-matrix addition. Matrix-matrix subtraction. ...
37 views

### A matrix-vector multiply parallelized using boost::MPI

This program performs a matrix-vector multiply using MPI to split the computation up. It is not extremely robust (for example, it doesn't handle the case where the number of MPI processes does not ...
106 views

### GeeksforGeeks: Rotate matrix by 90 degrees

Please review the code readability, I would like to have an easier to follow code. Thanks ...
76 views

### 3-function program computing connected components of a point cloud given a distance matrix

I wrote this code in Haskell (instead of Python) for the educational benefit. Can anyone suggest ways to improve this code? I'm guessing that I'm using fromIntegral...
62 views

### Sums of columns and diagonals of a matrix

I made a simple matrix program that prints some data..I want to know how to reduce amount of lines with some functions or whatever, because there is so much if-s,and for loops. Tried to make ...
44 views

### Sum of Two Matrices

For a homework assignment, I was asked to do this problem. It worked, but it looks messy in my opinion. I want to know if this is the best way to accomplish this task, and if there can be any ...
43 views

### Lowest cost path through elements in a matrix

I've developed a program in Python that calculates the lowest possible costing path between two points in a matrix, including the values contained in the start and finish cells. The code is below. ...
66 views

### Computing the difference of the cross-totals of the diagonals of a matrix

I have solved a seemingly easy problem: Given a square matrix, calculate the absolute difference between the sums of its diagonals. For example, the square matrix is shown below: \begin{bmatrix}...
137 views

### Search for row number of maximum value in matrix column

Background I'm writing code that searches for the row number of the maximum value in a partial column of a matrix. The partial column corresponds with the non-zero values of an equivalent lower ...
81 views

### Applying a function to each row of a matrix

My goal is to apply a function func1 to each row of the matrix input and then return a new one resulting from the transformation....
77 views

### Manually writing a function matrixpower() in R

Problem 1 - Matrix powers in R R does not have a built-in command for taking matrix powers. Write a function matrixpower() with two arguments mat and k ...
125 views

### Matrix class with space-optimized triangular (lower and upper) variants

I've written a class for square numerical matrices (of doubles, in this case), in C++11. Since I intend to use this class later ...
60 views

### Applying a function to columns of two matrices producing their combinations

I made a short snippet for applying a function f that takes two arguments (vectors) to columns of two matrices producing all possible combinations of those columns. ...
278 views

### Computing a Discrete Cosine Transform matrix

I'm learning Haskell and I needed to work with discrete cosine transform matrices, so I made a program that generates text (usable in WolframAlpha) containing the generated matrix. The elements of ...
59 views

### Transpose of a very large matrix with fewer than 1021 rows with Python

I have a matrix of fewer than 1021 rows. I'd like to take its transpose, but it is too big for GNU datamash and awk solutions to ...
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### Calculating the potential of a matrix of size (424600, 55)

I have the following working code to calculate the potential of a matrix after normalizing the matrix. But it is too much time consuming. Is there a way to make this code run faster? ...
59 views

### Reading sparse matrix from binary file

I have binary files containing sparse matrices. Their format is: number of rows int length of a row int column index int value float Reading ...
94 views

### JavaScript Spiral Matrix Coding Challenge

A whiteboarding challenge: Given a 2D array (matrix) inputMatrix of integers, create a function spiralCopy that copies ...
75 views

### Decomposing a matrix as a sum of two bitstrings

I chanced upon this question and came up with the following algorithm, looking for criticisms and advice on how to improve my algorithm efficiency. You are given 3 arguments: A & B are ...
109 views

### Perturbed phase oscillator integration

I am integrating a system of perturbed phase oscillators. I define the system of equation and also the Jacobian matrix. I have to reshape the one dimensional vector of system state to a 2 dimensional ...