# 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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### 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 ...
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### Traceback in sequence alignment with affine gap penalty (Needleman-Wunsch)

I am working on an implementation of the Needleman-Wunsch sequence alignment algorithm in python, and I've already implemented the one that uses a linear gap penalty equation for scoring, but now I'm ...
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Please check the code to see if there anything I can improve . Everyting is working as expected. matrix.h ...
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### HackerRank NCR codesprint: Spiral Message

Problem statement: https://www.hackerrank.com/contests/ncr-codesprint/challenges/spiral-message You've intercepted an encoded spy message! The message originated as a single line of one or more ...
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### HackerRank - Matrix Rotation

Problem statement Given a matrix (up to 300 × 300), rotate each element R steps anti-clockwise along concentric rectangular paths (R up to 109). The algorithm is rated as hard on HackerRank. On ...
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### Generalized NumPy reshape function to imitate einsum syntax

I often perform a lot of reshape(), transpose() or squeeze() operations on ...
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### Probabilistic Matrix Inspection - Suggested by a paper, implemented by me

I have read this paper and I actually found it interesting. This is an attempt to implement the proposed algorithm. I would like to know: Is my algorithm correct by what is discribed in the paper? ...
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### Converting state matrices to adjacency matrices to thresholded matrices

I am currently taking part in research utilizing Naked Mole Rats. I am utilizing data analysis techniques to answer the overall question, "Can we detect certain types of naked mole rat behavior ...
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### Find diagonal positions for bishop movement

In a chess board, I need to find the diagonals a bishop can move on, and more specifically, the coordinates of those squares. So, given a grid of any size and a position in that grid (expressed in ...
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### 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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### Matrix of constrained sums using R

In this post, I asked a question regarding how to create a matrix of integers where elements in each row satisfy a particular property. The notation in the original post is a bit cumbersome so I ...
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### Online Principal Component Analysis with spectral bounds

I have question regarding online PCA implemented in the paper. I am interested in the Algorithm 2. I am not certain if there is a bug in my code can someone confirm if my code is correct? The ...