Questions tagged [matrix]

A matrix is a list of numbers arranged in a rectangle with rows and columns. In programming, it is also known as a 2D array. Use this tag if your challenge is about manipulating matrices.

Filter by
Sorted by
Tagged with
21
votes
16answers
2k views

Verify Eigenpairs

In this challenge, you will be given a square matrix A, a vector v, and a scalar λ. You will ...
14
votes
9answers
575 views

Lists and arrays, part by part

In this challenge, you'll get four different but somewhat related tasks that must be solved in a specific manner. First, I'll explain the tasks, then follows an explanation of how you must solve it. ...
13
votes
6answers
1k views

Evaluate a simple spreadsheet

Rules No cell range references (A2:B3). Maximum 9 rows and 9 columns. No circular references or formula errors. Empty cells evaluate to ...
21
votes
41answers
3k views

Robbers: Crack the regex - Make a snake

This is the robber's thread. The cop's thread is here. A snake matrix is a square matrix that follows this pattern: 3-by-3: 1 2 3 6 5 4 7 8 9 and 4-by-4: ...
41
votes
51answers
7k views

Cops: Make a regex - Make a snake

This is the cop's thread. The robber's thread is here. Write a code that takes an input n and creates a n-by-n "snake matrix". A snake matrix is a matrix that ...
30
votes
4answers
1k views

Rotating a 2D Matrix

Let's say I have the following (2D) matrix: [[1, 2, 3, 4 ], [5, 6, 7, 8 ], [9, 10, 11, 12], [13, 14, 15, 16]] Rotate the matrix counterclockwise ...
15
votes
5answers
578 views

Find the submatrix with the smallest mean, 2.0

You're given a n-by-m matrix of integers, where n,m > 3. Your task is to find the 3-by-3 sub-matrix that has the lowest mean, and output this value. Rules and clarifications: The integers will be ...
21
votes
14answers
1k views

Find the submatrix with the smallest mean

You're given a n-by-m matrix of integers, where n,m > 3. Your task is to find the 3-by-3 sub-matrix that has the lowest mean, and output this value. Rules and clarifications: The integers will be ...
28
votes
10answers
3k views

Symbolic matrix multiplication

There are lots of different ways to explain matrix multiplication. I'll stick with a single figure since I believe most people here are familiar with it (and the figure is very descriptive). If you ...
12
votes
9answers
634 views

Construct a Gaussian Matrix

Gaussian blur is a method used for blurring images smoothly. It involves creating a matrix which will be used by convolving it with the pixels of an image. In this challenge, your task is to construct ...
8
votes
4answers
647 views

Find the rows which make each column have one True (was: Knuth's Algorithm X)

Task Given a Boolean matrix, find one (or optionally more) subset(s) of rows which have exactly one True in each column. You may use any algorithm, but must support very large matrices, like the last ...
13
votes
11answers
997 views

Turn this array into a matrix

Take a non-nested array as input. Turn it into a matrix by using the following method: Let's say my array is [1, 2, 3, 4, 5] First, I repeat that array 5 times: (...
23
votes
17answers
2k views

Is it a stochastic matrix?

A stochastic matrix is a matrix of probabilities used in the context of Markov chains. A right stochastic matrix is a matrix where each row sums to 1. A left ...
14
votes
21answers
2k views

Do Matrix Multiplication!

In mathematics, matrix multiplication or the matrix product is a binary operation that produces a matrix from two matrices. The definition is motivated by linear equations and linear transformations ...
9
votes
3answers
459 views

Code golf a random orthogonal matrix

An orthogonal matrix is a square matrix with real entries whose columns and rows are orthogonal unit vectors (i.e., orthonormal vectors). This means that M^T M = I, where I is the identity matrix ...
10
votes
4answers
267 views

Compute the perimeter density matrix

Introduction The perimeter density matrix is an infinite binary matrix M defined as follows. Consider a (1-based) index (x, y), and denote by M[x, y] the rectangular sub-matrix spanned by the corner (...
2
votes
2answers
173 views

N in a row (or column)! [closed]

N in a row Input: The character and a 2-Dimensional array. The array with a size of N x N where 1 <= N <= 26, it will ...
16
votes
3answers
430 views

Totally Invertible Submatrices

(inspired by this question over on Math) The Definitions Given an n x n square matrix A, we can call it invertible if there ...
97
votes
22answers
15k views

Where's the 0xBEEF?

This challenge was inspired by this Wendy's commercial from 1984. Illustration by T S Rogers Your task is to find a hexadecimal 0xBEEF on a binary bun. The 'beef' consists of the following pattern: ...
28
votes
9answers
4k views

Calculate the permanent as quickly as possible

The challenge is to write the fastest code possible for computing the permanent of a matrix. The permanent of an n-by-n matrix ...
20
votes
12answers
3k views

Codegolf the permanent

The challenge is to write codegolf for the permanent of a matrix. The permanent of an n-by-n matrix ...
5
votes
5answers
510 views

Image Smoothie!

Input into your program a black and white image. (png, jpg, etc) Convert the image to a 2D matrix of pixels, where each index is the grayscale value of the image. Take each index of the matrix and ...
9
votes
7answers
470 views

Fill in the grid randomly

Given positive integer n < 10, create a 2 dimensional matrix where each location is filled with its x and ...
14
votes
7answers
380 views

Generate binary matrices which are distinct up to reflections

Here are all the 2x2 binary matrices ...
23
votes
16answers
2k views

Create a pyramidal matrix

A pyramidal matrix is a square matrix where all numbers increase or decrease from the center point, like the two matrices below: ...
23
votes
19answers
6k views

Dijkstra's Challenge

Presented in honor of APL as an interactive tool turning 50 this year Background Ken [Iverson] presented his paper Formalism in Programming Languages in August 1963 at a Working Conference on ...
9
votes
6answers
466 views

Index sum and strip my matrix

Index sum and strip my matrix Given a matrix/2d array in your preferable language Input: The matrix will always have an odd length The matrix will always be perfectly square The matrix values can ...
16
votes
9answers
837 views

Alternating sign matrix verification

An alternating sign matrix is an n by n matrix consisting of the numbers -1, 0, 1, such that: The sum of each row and column is ...
10
votes
13answers
431 views

Dot Product of Diagonals

This challenge is very simple. You are given as input a square matrix, represented in any sane way, and you have to output the dot product of the diagonals of the matrix. The diagonals in specific are ...
18
votes
5answers
934 views

Jordan Decomposition

Important note: Because this challenge only applies to square matrices, any time I use the term "matrix", it is assumed that I am referring to a square matrix. I am leaving off the "...
13
votes
8answers
2k views

Matrix Trigonometry

Introduction The two most common trigonometric functions, sine and cosine (or sin and ...
11
votes
7answers
1k views

Calculate the Kronecker Product

Related, but very different. In the examples below, A and B will be 2-by-2 matrices, and the matrices are one-indexed. A ...
9
votes
10answers
787 views

Find the Matrix Power

Problem Create a program or function that can calculate the result of a matrix raised to the nth power. Your code will take an arbitrary square matrix A and a non-negative integer n, and return a ...
16
votes
8answers
872 views

Transform a matrix

Write a program or function where a matrix A (maximum value of dimensions of the matrix is 100) is transformed to a new matrix B. Each element of the new matrix B is the sum of the positive neighbors ...
9
votes
6answers
788 views

Calculate the Kronecker sum of two matrices

In the examples below, A and B will be 2-by-2 matrices, and the matrices are one-indexed. A Kronecker product has the ...
4
votes
1answer
172 views

Find the last position in a matrix walking like a spiral [closed]

This question will be deleted soon, do not read/answer it Introduction Given one matrix A x A and a number of movements N. ...
21
votes
18answers
2k views

Diamondize a Matrix

Given a matrix, output a representation of the matrix where the top left element is on top, the anti-diagonal is the central row and the bottom right element is at the bottom. For example, consider ...
15
votes
18answers
1k views

Sorting rectangular matrices

Given a matrix A, we can say that it is "sorted" if each row and column of A is sorted (ascending left-to-right for ...
19
votes
7answers
933 views

Hilbert-Curvify a Matrix

Inspired by this question Another way to unroll a 2D image into a 1D string is to use an Hilbert Curve. There are many version of this curve, depending on the number of iterations used while ...
18
votes
3answers
712 views

Reconstruct a zigzagified matrix

As part of its compression algorithm, the JPEG standard unrolls a matrix into a vector along antidiagonals of alternating direction: Your task is to take the unrolled vector along with the matrix ...
43
votes
10answers
4k views

Zigzagify a Matrix

As part of its compression algorithm, the JPEG standard unrolls a matrix into a vector along antidiagonals of alternating direction: Your task is to take a matrix (not necessarily square) and return ...
21
votes
7answers
1k views

Is this a submatrix?

This is the 2-dimensional generalisation of this challenge. For our purposes, one matrix (or 2D array) A is considered a submatrix of another matrix B, if A can be obtained by completely removing a ...
11
votes
3answers
643 views

Rotate every 2x2 block in a matrix

The Challenge Given a n x m matrix with n > 1 and m > 1 filled with integers 1 2 3 4 ...
15
votes
4answers
671 views

Rotate every row and column in a matrix

The Challenge Given a n x n matrix of integers with n >= 2 1 2 3 4 and a list of integers with exactly ...
25
votes
17answers
1k views

Vandermonde Determinant

Given a vector of n values (x1,x2,x3,...,xn) return the determinant of the corresponding Vandermonde matrix. This determinant ...
17
votes
11answers
1k views

Recursive 2x2 determinant

The determinant of a 2 by 2 matrix a b c d is given by ad - bc. Given a matrix of digits with dimensions 2n by 2n, n ≥ 1, ...
25
votes
14answers
1k views

Fibonacci-style matrix expansion

For each row and then column of a matrix, we can add an extra entry with the sum of the last two entries in that row or column. For example with the following input matrix: ...
44
votes
84answers
5k views

Construct the Identity Matrix

The challenge is very simple. Given an integer input n, output the n x n identity matrix. The identity matrix is one that has <...
18
votes
6answers
845 views

Cofactor Matrices

The cofactor matrix is the transpose of the Adjugate Matrix. The elements of this matrix are the cofactors of the original matrix. The cofactor (i.e. the element of the cofactor matrix at row i and ...
14
votes
12answers
749 views

Construct a companion matrix

You have a number of polynomials who are lonely, so make them some companions (who won’t threaten to stab)! For a polynomial of degree n, there is an ...