# 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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### Matrix Implementation using struct in C

Follow up on this post. I have refactored my code and created a matrix_t struct and implemented various functions to create, delete, modify and perform arithmetic on them. ...
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### Matrix multiplication using functions in C

This exercise surprised me a little bit. I did not expect that gcc (GCC 6.3.0 in the MinGW suite) would use the C11 standard by default, which I realised after I ...
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### numpy performance of norm calculation using variable dimension

I am looking for advice to see if the following code performance could be further improved. This is and example using a 4x3 numpy 2d array: ...
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### Map square coordinates in matrix to flat array indices without hurting performance

I'm more like playing and the problem I'm going to demonstrate is a learning task, so to speak, not something I really need to solve. Imagine having a matrix of data. You chose square in it and ...
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### AVX SIMD in matrix multiplication

I have coded the following C function for multiplying two NxN matrices and using AVX vectors to speed up the calculation. It works but the speedup is not what is to be expected(some scalar code is ...
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### Normalization, division and reshaping processes on an HDF5 file

I performing a set of division operations and reshaping on a HDF5 file. As my datapoints is around 4000 in number it takes around a minute. I will be adding more data, which will further slow my ...
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### Array transposition

The task: take a byte[][] and transpose it. The complication: the original array is a result of a partition operation that might not be even, so the last subarray ...
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### Portable multithreaded matrix multiplication in C

I essentially took this progam, and made it compile and run on Windows too. Also, I incorporated some nice points made by Toby Speight. matrix.h ...
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### Multithreaded matrix multiplication on Unix in C

I have this program for comparing serial and parallel matrix multiplication algorithms: matrix.h ...
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### Improving the manipulation of 2D Arrays for an easy challenge on HackerRank with Python 3

I am practicing some exercises on HackerRank in order to improve my skills on Python3. I am doing the 30 days challenge. There is one challenge involving matrices. I was able to pass the test cases ...
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### Cor.test inside for loop is very slow for large matrix processing

I have a matrix of 36,000 genes measurements for 60 samples. For calculating most correlated genes of the first gene in the matrix, my following program gives the result. However processing time is ...
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### Counting neighbor cells of a matrix

I was given this problem to solve inside a Swift playground. I was vaguely told my answer is correct but not good enough. ...
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### Implementation of the Householder Transformation

I implemented the Householder transformation in Python, so that I can later use it in a QR decomposition. Unfortunately I haven't found a good concise source for reading up on the algorithm. I am not ...
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### Small calibration script for xinput

I've written this as an alternative to xinput_calibrator when it wasn't working for me. It's my first crack at several things: ...
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### Generic matrices implementation

I am implementing a litte generic math library. What I have done is to write my generic matrix and vector class. I'm curious if I have it done right so far (implementation wise not totally ...
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### Minimum number of moves to solve “game of fifteen”

I read about this game and tried to make my own algorithm to solve this. I asked it on StackOverflow for the appropriate algorithm and logic to solve this problem. With the help of answers over ...
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### Matrix multiplication with OpenMP parallel for loop

I tried implementing matrix multiplication with parallel for loop in OpenMP as follows. It runs correctly but I want to make sure if I'm missing anything. How does this determine the number of threads ...
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### How to make a matrix factorization system recommander faster?

I used and modified a matrix factorization function for a system recommender from quuxlabs.com. It works well for small sized input but when we get to large matrix it takes too much time. I was ...
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### Computing sum on column + sum on row + sum on each diagonal

I have the following problem: I read from a file the dimension(n) of the matrix(which is n * n) and the matrix. For each element ...
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### Make each element equal to its neighbouring element which is maximum in a matrix

I have a matrix and I want to make each of its element equal to the maximum of its neighbouring element and each time I increase number of counts till all the elements in the matrix becomes equal to ...
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### Multidimensional matrix exponentiation

Is there a more efficient way of exponentiating a multidimensional matrix? This is how I am currently doing it: ...
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### Backward transformation implementation for a barrel eye lens aberration in c++ 14 (using opencv)

I've made the following backwards transformation from a "transformed" source x,y point, to the resulting index of the actual image that I have, so I can avoid black spots appearing in my barrel eye ...
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This program is used to solve Challenge #140 [Intermediate] on /r/dailyprogrammer. The challenge is, given a input set of directed edges, print the corresponding ...
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### Counting Islands In Matrix Of Boolean

Code objective: Read a txt file, parse it into a matrix and count (and also print) the number of unique "islands" in the map formed by the matrix. 0 = Sea; 1 = Land; Islands are orthogonal groups of ...
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### Matrix transpose algorithm

If I have a List<List<T> like the following : Name City Id Anna NY 1 Joe NJ 2 How can I ...
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### Blurring an image using matrices

Suppose there is a very big matrix and and a small window is moving on the matrix. The small window will move right and down, step by step (means each time move one step right, or move one step down). ...
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### GPU and CPU templated matrix classes

I'm learning CUDA C++ (and C++). Can you guys give me some feedback on my basic templated matrix implementation? A brief explanation of my decisions: First things first: I can't use STL classes/...
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### C++ Template Matrix Class - WIP

I've created simple matrix class in c++ and I would like to know what you think about the code. I've left the implementation in header file for simplicity for now. The class is not finished yet, it ...
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### Java Matrix multiplication using Multithreading

I am trying to achieve matrix multiplication using the concept of concurrency and cyclic barrier. Here is the code snippet:- ...
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### Find all sub matrices of type N*M in it which are palindromic

Today I had an interview, where I was asked to solve this question. A $N*M$ matrix is called a palindromic matrix, if for all of its rows and columns, elements read from left to right in a row are ...
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### Matrices in C implementation

I recently wrote a C implementation of Matrices with add, subtract, and multiply. I want to expand this out eventually where I can diagonalize, efficiently square, row-reduce, etc... I was wondering ...
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### Print diagonal numbers of matrix in ascending order

Today I attempted an interview problem: Q: An n×n matrix contains numbers from 1 to n×n and is generated in the fashion: The first row is of numbers starting from 1 to n left to right, ...
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### LeetCode 01: Matrix challenge

Recently, I've solved the "01 Matrix" LeetCode problem and the solution was accepted by the LeetCode OJ: Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell. ...
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### Recursive matrix multiplication in C++

I'm working through CLRS, and I'm hoping to get some pointers (ha!) on my C++ coding style and the way I've implemented recursive matrix multiplication. The code right now seems a bit complex for ...
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### Matrix OOP implementation using C++11 and C++14

I know that other people already did the same already, but I'm learning C++ (C++11/14) coming from C (I'm reading Programming: Principles and Practice Using C++, by Bjarne Stroustrup), and this is 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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### Multithread the variant of matrix multiplication

This is matrix multiplication. Big matrix split on the submatrix and multiplication in parallel, result matrices merge to result. How i can make this code better? ...
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### Efficient extraction of patch features over an image

Input: data - a matrix of size n*m*3*3 (complex values) indices - a list of coordinates (x,y), where x < n and y < m fp - a feature parameter which is a tuple of ((fp11, fp12), (fp21, fp22)), ...
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### Hackerrank Queen's Attack II

Problem statement A queen is standing on an $n$x$n$ chessboard. The chessboard's rows are numbered from $1$ to $n$, going from bottom to top; its columns are numbered from $1$ to $n$, ...
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### Basic Templated Matrix Library

I am a beginner C++ programmer and I have been working on a library to use for working with matrices. The library main features should be Working with matrices (addition, subtraction, arbitrary ...
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### LSH hashcode generator function

For building an LSH based system in Python, I need to have a very fast calculation of the hashcode. I won't need to explain here the LSH algorithm itself, but I need help in improving performance of ...
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### Find element in 2D matrix where rows and columns are sorted

Elements of a matrix are given in sorted rows and columns. I want to find the element in an optimized way. First, I will get the last element of a row, which will determine if a number can exist in ...
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### Encryption by transposing text in a grid

I wrote a Java program that given a text message will print the encoded message. The problem is described in this link. Summary: We have to write a program that will encrypt a message that do not ...
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### Read matrix from file, the C++11/14 way

I am trying to get acquainted with C++11/14, so please tell me if the code below could be written in a more "modern" way. Or, of course, if it could be improved in any way. The function ...
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### 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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### Tetris-like algorithm (2D matrix)

The algorithm should be checking if the block fits perfectly when it falls. The block is always the same shape: .##.... ..##.... Keep in mind I wrote this ...