All Questions
283
questions
11
votes
15
answers
2k
views
Is this a Hadamard matrix?
Hadamard matrices is a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal.
In other words, it means that each pair of rows has matching entries in exactly half of ...
- 4,167
12
votes
6
answers
1k
views
Contract a tensor
Introduction
Tensor contraction is an operation that can be performed on a tensor. It is a generalization of the idea of the trace of a matrix. For example, if we have a rank-2 tensor (a matrix) and ...
- 2,093
9
votes
5
answers
922
views
Compute the logarithm of a matrix
There have already been challenges about computing the exponential of a matrix , as well as computing the natural logarithm
of a number. This challenge is about finding the (natural) logarithm of ...
- 6,035
17
votes
22
answers
2k
views
Compute this fractal matrix
The unique-disjointness matrix ( UDISJ(n) ) is a matrix on all pairs of subsets of {1...,n} with entries $$ U_{(A,B)}=\begin{cases}
0, ~ if ~ |A\cap B|=1\\
1, ~ ...
- 6,035
24
votes
40
answers
2k
views
Diagonalize a vector
Diagonalize a vector into a matrix.
Input
A vector, list, array, etc. of integers \$\mathbf{v}\$ of length \$n\$.
Output
A \$n \times n\$ matrix, 2D array, etc. \$A\$ such that for each element \$a_i \...
- 10.2k
23
votes
29
answers
2k
views
Borders of a Rectangular Matrix
Although it's done a few times as sub-challenge of a larger challenge, and we also have a challenge to remove the borders of a square matrix, I couldn't find a challenge to output the borders of a ...
- 128k
11
votes
6
answers
727
views
Calculate the Smith normal form of an integer matrix
Given an \$m \times n\$ matrix of integers A, there exist a \$m \times m\$ matrix P, an \$m \times n\$ matrix D, and an \$n \times n\$ matrix Q such that:
\$A = P D Q\$.
P and Q are unimodular ...
- 1,391
14
votes
13
answers
2k
views
Make a Custom Bayer Matrix
A Bayer matrix is a threshold map used for ordered dithering that gives the illusion of having more shades of color than actually present by using a crosshatch-like pattern.
Bayer matrices are square ...
- 4,040
4
votes
1
answer
206
views
4D rotation matrix to quaternions
It is well-known that a 3D rotation can always be represented by a quaternion. It is less well-known that a 4D rotation can always be represented by two quaternions, sending a point \$p=(a,b,c,d)^T\$ ...
- 3,845
9
votes
5
answers
479
views
3D rotation matrix to quaternion
There are multiple ways to represent a 3D rotation. The most intuitive way is the rotation matrix –
$$A=\begin{bmatrix}A_{11}&A_{12}&A_{13}\\A_{21}&A_{22}&A_{23}\\A_{31}&A_{32}&...
- 3,845
11
votes
9
answers
658
views
Find Sub-matrix with matched cell 1
You are given a matrix of size m x n where each cell can contain either 1 or 0. You need to find the largest square submatrix that contains only 1's. The output should be the area of the largest ...
user116868
16
votes
14
answers
1k
views
Painting with Line Filler
Given a matrix of positive integers, output whether it's possible to generate it by starting with an empty1 matrix of the same dimensions and repeatedly filling a whole row or a whole column with the ...
- 25k
16
votes
12
answers
1k
views
Is this a shift matrix?
A Shift matrix is a binary matrix with one superdiagonal or subdiagonal formed by only ones, everything else is a zero.
A superdiagonal/subdiagonal is a diagonal parallel to the main diagonal, which ...
- 9,408
3
votes
1
answer
195
views
Implement Strassen's algorithm [closed]
Strassen's algorithm was the first method of matrix multiplication in subcubic time complexity, namely O(n**log2(7)) for a pair of ...
- 97
9
votes
8
answers
434
views
Find the representative submatrix
Note: This is a more limited version of a challenge from 2014 that only received one answer. That challenge required participants write two programs; this challenge is essentially one half of that. ...
- 10.1k