All Questions
10 questions
9
votes
1
answer
357
views
Matrix obtained by recursive multiplication and a cyclic permutation
Have you ever seen this matrix? Each row is obtained from the previous one by multiplying each element by the corresponding element of the next cyclic permutation of $(a_1,\dots, a_n)$:
$$\left(
\...
- 93
8
votes
1
answer
1k
views
Is there an efficient algorithm to check whether two matrices are the same up to row and column permutations?
Define $\mathcal M_n$ as the set of all $n\times n$ matrices with each entry either 1 or $x$. Two such matrices are equivalent iff they can be obtained from each other by swapping pairs of rows and ...
- 13.4k
6
votes
1
answer
448
views
Counting the (additive) decompositions of a quadratic, symmetric, empty-diagonal and constant-line matrix into permutation matrices
Dear community,
I have the following combinatorial question which I will explain in short first and then with some more detail. At the end you will find a very simple example.
Short version
Le $A \...
- 199
6
votes
1
answer
726
views
Combinatorics and symmetry in matrices under row and column swaps
Suppose we have a $m\times n$ matrix and a sequence of numbers with which to fill the matrix, $\{c_1,c_2 \dots c_k \}$. I like to think of the numbers as colors, hence the notation. How many unique ...
6
votes
1
answer
500
views
Rank and frequency of permutations
(a) Let $[n] = \{1,\dotsc,n\}$, and let $\pi:[n]\to [n]$ be a permutation. Define an $n$-by-$n$ matrix $A=A(\pi)$ as follows: $A_{i,j}=1$ if $j>i$ and $\pi(j)>\pi(i)$, $A_{i,j}=-1$ If $j<i$ ...
- 20.2k
3
votes
2
answers
316
views
Relation graph isomorphism to discrete logarithm
$\DeclareMathOperator\ora{ora}$Let $A_0$ be the adjacency matrix of graph $G$ and $P_0$
permutation matrix of multiplicative order $\rho$.
Let $X$ be positive integer and $B_0=P_0^X A_0 P_0^{-X}$.
Q1 ...
- 25.4k
3
votes
2
answers
543
views
Number of $\{0,1\}$ matrices with distinct rows and distinct columns
How many $M\in\{0,1\}^{r\times c}$ are there such that each row and each column of $M$ is distinct?
How many classes of matrices in $\{0,1\}^{r\times c}$ up to permutation equivalence are there such ...
user94040
2
votes
1
answer
140
views
Minimum local permutation data needed to globally merge locally sorted sequences?
We have $k$ blocks of integer sequences $B_1,\dots,B_k$ where $B_i$ is a sequence $$a_{i,1},\dots,a_{i,n_i}$$ with $a_{i,j}\leq a_{i,j+1}$.
Denote the permutation matrix $M_{\ell,\ell'}$ that merges $...
- 1,826
2
votes
0
answers
71
views
Are the ranks of the following matrices given by these simple expressions?
The question itself is formulated in the title, so below I specify the matrices and expressions mentioned there. In case if this is something known or can be easily deduced from something known, this ...
- 321
1
vote
1
answer
209
views
Deciding if given number is a permanent of matrix
The permanent of an $n$-by- $n$ matrix $A=\left(a_{i j}\right)$ is defined as
$$
\operatorname{perm}(A)=\sum_{\sigma \in S_{n}} \prod_{i=1}^{n} a_{i, \sigma(i)}
$$
The sum here extends over all ...
