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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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
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5answers
303 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
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16answers
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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 ...
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20answers
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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 ...
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16answers
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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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15answers
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Find the Cell's Neighbours
...or Toroidal Moore Neighbourhoods
Given positive integers h, w and a non-negative integer ...
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28answers
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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] \...
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16answers
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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]
[...
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votes
3answers
372 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 ...
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11answers
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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
539 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 ...
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1answer
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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:
...
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votes
2answers
313 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 ...
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votes
13answers
277 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....
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12answers
818 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
263 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 ...
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16answers
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50answers
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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
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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 ...
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15answers
533 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 ...
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votes
11answers
886 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
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20answers
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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 ...
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votes
10answers
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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
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17answers
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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
357 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
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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
203 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 ...
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votes
7answers
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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
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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
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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
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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
818 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 ...
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4answers
166 views
Flattened Spiral Permutation Index
Context
Consider square matrices with n columns and rows containing the first n^2 (i.e. n ...
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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 ...
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34answers
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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 ...
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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.
...
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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
161 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 ...
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votes
27answers
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Generalized matrix trace
Inspiration.
Given (by any means):
A two-argument (or single argument consisting of a two-element list) black box function, f: ℤ+ × ℤ+ → ℤ+ (input and output are ...
26
votes
29answers
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Rotation summation
Take a square matrix containing positive integers as input, and calculate the "rotated sum" of the matrix.
Rotated sum:
Take the sum of the original matrix and the same matrix rotated 90, 180 and ...
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votes
20answers
1k views
Compute the Optimal Square Matrix
The optimal matrix (for the rather narrow scope of this challenge) is obtained by "zipping" the elements from the corresponding rows and columns of a square matrix and getting the maximum of each pair....
16
votes
7answers
608 views
Queue Our Decomposition
In this challenge I will ask you to find a QR decomposition of a square matrix. The QR decomposition of matrix A is two Matrices Q and R such that A = QR. In particular we are looking for Q to be an ...
3
votes
0answers
78 views
lexicographically sorted list of index [closed]
Given a drawing of the letter shoot system, where an existing piece of pipe is marked with a *, and an empty spot is marked with a ., your task is to compile a lexicographically sorted list of index ...
33
votes
40answers
3k views
Is my Matrix Arrowhead?
Definition
An arrowhead matrix is a matrix that has all entries equal to 0, except the ones on the main diagonal, top row and leftmost column. In other words, the matrix should look like this:
* * * ...
