# Tagged Questions

0answers
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### Looking for an algo to “sorta” diagonalize a similarity matrix.

I've got a big fat similarity matrix. The rows and columns represent people, and the values represent some positive measure of their closeness (0 meaning no connection at all). The n-th row and n-th ...
0answers
17 views

### How to perform parallel cholesky factorisation

I am a student trying to understand and implement a parallel cholesky factorisation algorithm for sparse matrices in software. Can anyone give an example of a parallel cholesky factorisation ...
0answers
50 views

### Fast checking Matrix multiplication in mod 10

I recently faced this problem in a programming contest: Given 3 square matrices N x N of size N up to 1000. All elements in 3 matrices are from 0 to 9. Check if matrix A x B equals to C, mod 10. In ...
0answers
80 views

### Quaternion conversion

We have a normalized orthogonal co-ordinate frame travelling through the curve as in figure 1 below, from one end to other. Let us call starting end as A and ending end as B. What we know is initial ...
0answers
40 views

### Fastest Algorithms for Determining the Nullity of a Matrix

How exactly does one go about determining the Nullity of a Matrix quicker than simply running Gaussian Elimination on the matrix itself? To be perfectly honest I can't think of a method that doesn't ...
1answer
42 views

### Why is Doolittle Decomposition Algorithm failing and what should I try next?

I am trying to find the LU Decomposition of the following matrix: So far I have only tried the Doolittle Decomposition algorithm with partial pivoting (it's never failed me before!). As far as I can ...
0answers
59 views

### Sparse matrix algorithms involving data-driven or random access / walk

I am looking for some well-known algorithms in which sparse matrix elements are accessed in a non-structured way, i.e. row/column depends on a value of another (sparse) matrix/vector element or some ...
1answer
139 views

### Tree Traversal - Simple Puzzle type Issue.

This is a puzzle like question,based on Fibonacci like structure of the tree. Actually it is a short question with out any complex concepts. It appears bit big,since I have added explanations with ...
0answers
29 views

### Strassens Matrix Multiplication Algorithm to compute product of 2 4X4 Matrices

Im trying to learn starssens matrix multiplication Algorithm.So far i know that it uses 7 multiplications and replaces a multiplication by several additions and subtractions,to achieve better ...
1answer
27 views

### The probability of getting a certain image by random pixelation

Well, seeing that I'm terribly bad at math I don't know how to solve this, I'll try to explain, excuse me if I sound dumb. Just suppose that I've got a photo/image with 320x240 resolution and 24 bit ...
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### Finding smaller matrix in bigger matrix

Given a bigger matrix of size R*C .Where each element of matrix is between [-20,20]. Now i need to find a smaller matrix of dimension H*W (H <= R, W <= C) in such a way that sum of squared ...
0answers
195 views

### How to distribute 5-digit numbers in 5x5 matrices

I have 98000 5-digit numbers, from 00001 to 98000. I need to distribute these 98000 numbers in 14000 5x5 matrices. A matrix cell must contain only a digit from 0 to 9. Each matrix must receive 7 ...
0answers
20 views

### Ordering binary matrices for reflection/rotation

I have a collection of $n\times n$ binary matrices and I would like to reduce it for symmetry ($D_4$ -- reflections and rotations). The naive method of testing each pair is very slow because the ...
1answer
49 views

### Computing eigenvalues of principal submatrices of Kronecker product of two PSD matrices

Given two PSD matrices $A \in R^{n \times n}$ and $B \in R^{m \times m}$ with eigenvalues $\lambda_i$ and $\mu_j$ respectively, the eigenvalues of the Kronecker product $A \otimes B$ are given by ...
3answers
33 views

### Performing matrix chain multiplication by hand

I'm trying to gain intuition for writing a matrix chain multiplication algorithm by working through a few problems by hand. I see plenty of worked-through solutions on sets of three or four solutions, ...
3answers
44 views

### How to combine Unitary Matrices in a clever way?

I am trying to implement genetic-type algorithms on unitary matrices. Hopefully I should be able to use this question for the mutation part. But I am having an issue with the cross-over step. So here ...
2answers
78 views

### Algorithm to compute maximum permutation sum in matrix

Given a matrix $A_{n\times n}$ of real numbers, what fast algorithms do there exist to compute the maximum value of $a_{1,\sigma(1)}+a_{2,\sigma(2)}+\ldots+a_{n,\sigma(n)}$ over all permutations ...
3answers
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0answers
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### Make the whole matrix zero

Two matrixes with N rows and M columns are given. Let P[i][j] and A[i][j] be the jth element of the ith row of the first and second matrixes respectively. Now we want to make each element of second ...
0answers
172 views

### Find all possible paths in a Matrix

I'm looking for algorithms to find all paths in a 4 x 4 matrix. The rules are as follows You can move in any direction (up, down, left, right, and diagonally) The next square in the path must be a ...
0answers
61 views

### Rank Of A Matrix Under Special Conditions

Let A be a $N*N$ matrix. Now A is defined in a special manner: Each row of A is defined by two integers L and R ($0\le L,R\le {N-1}$), such that all elements from the $L^{th}$ to the $R^{th}$ are all ...
0answers
49 views

0answers
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### Does a matrix represent a bijection

We have a square binary matrix that represents a connection from rows to columns. Is there a way to tell if a bijection exists (other than checking for all possible bijections and iterating through ...
1answer
53 views

### How is this matrix called (two diagonals)?

I need to write an algorithm for solving this matrix but I wanted to first make a search online and that's why I need its name.