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.
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Output the anti-clockwise inward spiral of a 2D array
From this stackoverflow question
Given a 2D array of size \$ M \times N \$, output the values in a anti-clockwise fashion. The output must start from the outside to the inside and the initial point ...
18
votes
12answers
2k views
Is the Matrix Positive-Definite?
Introduction
Today we're gonna take care of the bane of first-year linear algebra students: matrix definiteness! Apparently this doesn't yet have a challenge so here we go:
Input
A \$n\times n\$ ...
5
votes
3answers
422 views
Ordinary Least Squares Regression
I am quite surprised that a variant of linear regression has been proposed for a challenge, whereas an estimation via ordinary least squares regression has not, despite the fact the this is arguably ...
10
votes
7answers
609 views
Whose neighbours are hostile?
Introduction
For the purposes of this challenge, we will define the neighbours of an element \$E\$ in a square matrix \$A\$ (such that \$E=A_{i,j}\$) as all the entries of \$A\$ that are immediately ...
21
votes
14answers
2k views
Chop off the matrix to get the desired sum
Definition
Given a matrix \$M\$ of non-negative integers and a non-negative integer \$k\$, we define \$F_k\$ as the "chop-off" function that removes all rows and all columns in \$M\$ that contain \$k\...
18
votes
14answers
916 views
Square-Random-Symmetrical
Challenge
Write a program or a function that returns or prints a square-random-symmetrical matrix.
Input
N: The size of the matrix i.e 6 x 6
Output
The matrix. ...
20
votes
11answers
2k views
A knight's graph on an N-by-N board
In chess, a knight can only move to the positions marked with X relative to its current position, marked with ♞:
A Knight's Graph is a graph that represents all legal moves of the knight chess piece ...
11
votes
5answers
312 views
Minimal Centrosymmetrization
Topically related.
Objective: Given a matrix of positive integers \$M\$, output the smallest centrosymmetric matrix which contains \$M\$ (this matrix may contain non-positive integers as well).
A ...
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16answers
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16answers
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Roman Army Shields
Sandbox post (deleted)
The old roman army formations are very famous around the world. In these formations roman legionaries grouped in a geometric shape (usually a rectangle) protecting the flanks ...
26
votes
16answers
3k views
Beware of the matrix tornado!
The matrix tornado is just like any other tornado: it consists of things rotating around a center. In this case, elements of the matrix instead of air.
Here is an example of a matrix tornado:
First ...
18
votes
20answers
1k views
Collapsing Matrices
Related: Let's design a digit mosaic, Print/Output the L-phabet. Sandbox post here
Given 2 inputs C = columns and rows, S = starting point output a matrix as ...
22
votes
16answers
3k views
Find the inverse of a 3 by 3 matrix
Challenge
Given nine numbers, a, b, c, d, e, f, g, h, i, as input which correspond to the square matrix:
$$\mathbf{M} = \begin{pmatrix}a& b& c\\ d& e&...
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votes
15answers
1k views
Find the Cell's Neighbours
...or Toroidal Moore Neighbourhoods
Given positive integers h, w and a non-negative integer ...
37
votes
28answers
4k views
Is the matrix centrosymmetric… and so is the code?
Defintion
A centrosymmetric matrix is a square matrix that is symmetric about its center. More rigorously, a matrix \$A\$ of size \$n \times n\$ is centrosymmetric if, for any \$i,\: j \in ([1, n] \...
4
votes
16answers
509 views
2D Array Middle Point
Given dimensions of a 2D array, except 1xn, that results in an odd number of elements, find the midpoint index.
Example: Input is 3x5, representing the 2D array
[0,0] [0,1] [0,2] [0,3] [0,4]
[...
5
votes
3answers
393 views
Saddle points in a matrix
A matrix can be thought of as the altitudes of a surface in 3D space.
Consider the 8 neighbours (orthogonal and diagonal) of a cell as a cyclic sequence in clockwise (or anticlockwise) order. Some ...
12
votes
11answers
1k views
Find the Number With the Highest Sum of Neighbors
The Challenge
Given a grid of numbers (10 <= N <= 99)
Return number with the highest sum of the four numbers adjacent to it; that is the numbers above, below, right, and left of the number, but ...
16
votes
8answers
553 views
Classify a region by its slope
Definitions
The kth ring of a square matrix of size N, where 1 ≤ k ≤ ceiling(N/2) is the list formed by the elements of the kth and (N-k+1)th rows and columns, but without the first and last k-1 ...
2
votes
1answer
105 views
Array-of-array string conversion to and from matrix [closed]
Matrix challenges are popular. There's an issue of how to provide test cases. A common method is the row-wise array-of-arrays representation, such as:
...
18
votes
2answers
316 views
Is this a Weyr matrix?
There's a type of n×n matrix W called the basic Weyr canonical form. Such a matrix is described by its blocks and has the following properties, using the following reference diagram:
the main ...
0
votes
13answers
293 views
Beginners 10x10 multiplication matrix [duplicate]
I was looking for a very easy task to look how short of a code can be produced on a beginners exercise.
The goal is to produce a simple table that looks like this common java/c# code is about 4 lines....
11
votes
12answers
820 views
Sum of replicated matrices
Given a list of numbers [ a1 a2 ... an ], compute the sum of all the matrices Aᵢ where Aᵢ is defined as follows (m is the maximum of all aᵢ):
...
14
votes
3answers
278 views
Are there mountain rings?
Challenge
Given a matrix of positive integers, determine if there are any "rings" of mountains. The formal definition for this challenge is: given a matrix of positive integers, is there any positive ...
17
votes
16answers
732 views
26
votes
51answers
3k views
Orthodiagonal steps
It's a common problem to navigate in a 2D matrix. We've seen it many times and will see again. So let's help future us and develop the shortest solutions to generate all eight possible steps in a 2D ...
24
votes
12answers
2k views
Find arsonist's lullaby
Imagine an arsonist walking around the town and picking its victims according to a very specific pattern (Or, alternatively, Imagine a bee flying around the garden and picking its flowers to pollenize ...
10
votes
15answers
535 views
The biggest square
This question is similar to Biggest Square in a grid.
Challenge
Given a matrix of 1 and 0 in a string format ...
-3
votes
11answers
966 views
Getting the Vowel Square
Challenge
You will create a function which takes a matrix filled with letters from the alphabet and determine if a 2x2 square composed of vowels exists.
If a 2x2 ...
22
votes
20answers
3k views
Matrix in “slash” order
Given two positive numbers N >= 2 and N <= 100 create a matrix which follows the following rules:
First Number starts at ...
49
votes
10answers
7k views
Seats in a Finnish cinema
You're given the map of a cinema theatre as a boolean matrix: 0 represents a free seat, 1 - occupied. Each Finn who walks in chooses the seat farthest away (Euclidean distance) from the nearest ...
22
votes
17answers
1k views
Generate a Walsh Matrix
A Walsh matrix is a special kind of square matrix with applications in quantum computing (and probably elsewhere, but I only care about quantum computing).
Properties of Walsh matrices
The ...
11
votes
2answers
358 views
The Lonely Islands
Input:
A 2D array containing two distinct (optional) values.
I'll use 0 and 1 when explaining the rules. The input format is of course flexible.
Challenge:
Zeros are water, and ones are islands. In ...
25
votes
3answers
1k views
Golf A Free Lunch
Find a maximally profitable sequence of exchanges given an exchange rate table.
As an example consider the currencies Ariary (your home currency), Baht, Cedi, and Denar where the rate from one to ...
12
votes
5answers
211 views
Matrix trace for any matrix through… Bresenham’s line rasterisation
Inspired by this.
Agatha Stephendale, a sophomore who is really into raster graphics, has taken a course in linear algebra. Now she imagines matrices as rectangles, but in her artistic mind, she ...
10
votes
7answers
2k views
There, I fixed it (with rope)
Related: Rather similar (but much easier) challenge horizontally: There I fixed it (with tape)
Challenge:
Given a string only containing upper- and/or lowercase letters (whichever you prefer) and ...
10
votes
9answers
1k views
Convergence of a Markov Process
Challenge
Given a left- or right-stochastic matrix where the limit as x approaches infinity of the matrix to the power of x approaches a matrix with all finite values, return the matrix to which the ...
29
votes
7answers
2k views
We ended up where we started!…
Challenge:
Input:
You take two inputs:
- A string only containing printable ASCII (excluding spaces, tabs or new-lines)
- A printable ASCII character
Output:
The first line will contain the string-...
27
votes
31answers
3k views
Rebuild a rectangular array from a corner
I once had a beautiful rectangular array. It was very symmetrical, but unfortunately it has fallen apart and now I only have the top left corner. Your task will be to rebuild the original array.
Your ...
22
votes
13answers
2k views
Codegolf the Hafnian
The challenge is to write codegolf for the Hafnian of a matrix.
The Hafnian of an 2n-by-2n symmetric matrix ...
18
votes
20answers
2k views
How to print the below format in the fewest bytes?
This challenge is inspired by this, now deleted question.
Take a positive integer N as input, and output a matrix with the numbers 1 .. N2 that follows the pattern below:
Fill in the first row with ...
16
votes
18answers
3k views
Hermitian matrix?
Note that this challenge requires no handling or understanding of complex numbers.
Given a non-empty square matrix where every element is a two-element (Re,Im) integer list, determine (giving any ...
18
votes
10answers
1k views
Minimally sort a list into a matrix
Given an unsorted list of unique strictly positive integers, minimally sort it into a 2D matrix. The input list is guaranteed to be of composite length, which means the output matrix is not ...
14
votes
14answers
907 views
Generate all square sub-matrices of a given size
You will be given a square matrix of integers M and another positive integer n, strictly smaller than the size of M. Your task is to generate all square sub-matrices of M of size n.
For the purposes ...
8
votes
4answers
168 views
Flattened Spiral Permutation Index
Context
Consider square matrices with n columns and rows containing the first n^2 (i.e. n ...
70
votes
13answers
4k views
Friar simulator
The brethren from the order of St Golfus the Concise have a tradition of reciting a short prayer whenever they see someone make the sign of the cross. Due to the high level of sin measured among ...
16
votes
34answers
2k views
Perfect Squares Without Borders
Given n=m^2, return a list of integers that do not border the m x m grid of integers from ...
31
votes
13answers
4k views
Fryer simulator
Your task is to model the effects of batter on pieces of food. Please add three layers of crust.
...
19
votes
13answers
2k views
Check if all non-zero elements in a matrix are connected
Input:
A matrix containing integers in the range [0 - 9].
Challenge:
Determine if all non-zero elements are connected to each other vertically and/or horizontally.
Output:
A truthy value if all ...
16
votes
0answers
185 views
Matrices Generated Using Rectangles
Input is an r by c matrix of non-negative integers (you may input r and c as other parameters if this helps with golf). This may be inputted as a 2D array or, if you prefer, a 1D array (though taking ...
