Questions tagged [matrices]
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148
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Coefficients of a determinant of a matrix of univariate polynomials is in $GapL$
Given any matrix of univariate polynomials of degree $\leq n^{O(1)}$ then prove that the coefficent of $x^i$ in the determinant of the matrix is in $GapL$
Hint: Use Mahajan-Vinay's result of ...
- 288
6
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1
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342
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Condition Number dependent algorithms for matrix operations
Using the Conjugate gradient method we can solve a linear system $Ax=b$, where $A\in\mathbb R^{n\times n}$ in time $O(n^2 \sqrt{\kappa})$, where $\kappa=\frac{\sigma_\mathrm{max}(A)}{\sigma_\mathrm{...
- 958
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76
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Is there an algorithm for reducing the average row width of a sparse matrix?
Suppose I have a sparse $M \times N$ matrix $A$ and I define the "width" of each row $i$ to be:
$$w_i \equiv r(A_i) - l(A_i),$$
where $r(A_i)$ is the index of the rightmost nonzero element ...
- 131
3
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2
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824
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Johnson-Lindenstrauss and the largest eigenvalue of a matrix
Johnson-Lindenstrauss (JL) lemma shows that for any vector $u$ in $\mathbb{R}^d$, the vector $\frac{1}{\sqrt{k}}Ru$ satisfies $(1-\epsilon)\|u\|\leq \frac{1}{k}\|Ru\|^2\leq (1+\epsilon)\|u\|$ with ...
- 253
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computational complexity of sparse matrix powers
Given a sparse matrix $A$ with $nnz(A)$ denoting the number of non-zero entries in it. What is the computational complexity of computing $A^k$, for some positive integer $k$? As $k$ gets larger, I ...
- 209
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76
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Has there been any research on faster tensor inner products?
Matrix multiplication is a well studied problem which is recently back in the news due to deepmind.
That got me wondering has anyone looked at the more general problem of faster tensor multiplication? ...
- 369
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113
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Can one find any solution to this matrix problem in polynomial time?
I am given an M * N (M > 1, N > 1) matrix with all the numbers blackened but their row and column sums are visible.
For example, I am given this 3 * 3 matrix.
And one of the possible matrix ...
- 111
5
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321
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Deciding if all matrix multiplication entries have at least two witnesses
Consider two square matrices $A(x,y)$ and $B(y,z)$ of dimensions $N×N$ containing boolean entries. Consider the output product matrix $C(x,z)$ where $C=AB$ (not boolean matrix multiplication but the ...
- 1,177
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Sorting multiple columns of a matrix
Let $A \in \mathbb{R}^{n \times k}$ be a matrix where each column contains all of the numbers from $\{1,\dots,n\}$ in some arbitrary order. For example, if $n=3, k=2$, we could have
$$ A =
\begin{...
- 189
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111
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What type of Problems (Class and types) Can Be Solved Effectively with Quantum Computers?
The Question:
I'm trying to understand the type of problems that Quantum Computers are/will be good at solving and if there is a special class to categorizes these types of problems (e.g. Do we ...
- 109
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69
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Smallest nonzero eigenvalue of a sum of +1/-1 rank-one matrices?
Suppose we have a $k\times k$ matrix $A = \sum_{i=1}^{n} a_i a_i^T$ where $n \leq \mathrm{poly}(k)$ and each $a_i\in\{-1,1\}^{k}$. It is easy to prove that the largest eigenvalue of $A$ is at most $\...
- 31
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202
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Finding output with unique witness in matrix multiplication
Consider two square matrices $A(x,y)$ and $B(y,z)$ of dimensions $N \times N$ containing boolean entries. Consider the output product matrix $C(x,z)$ where $C = AB$ (not boolean matrix multiplication ...
- 1,177
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78
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Obtaining a lower bound of a matrix norm
I was wondering (on a setting where $\vec X_i \sim \mathcal{N}(\vec\mu, \mathbb{I})$ are $n$ random $d$-dimensional multivariate normal vectors with unknown mean $\vec\mu$) how I could obtain a lower ...
- 21
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120
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Solver for uniform matroid isomorphism
I want to solve the following coNP-complete problem efficiently in practice: Given a linear matroid represented as $k \times n$ matrix over a finite field $\mathbb{F}_p$ (where $p$ is large prime), ...
- 1,767
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Problem conditions to use Laplacian solvers
I am trying to use Laplacian Solvers to solve a linear equation. I am just learning it (form here), so my question is very basic and it might not even make sense.
Suppose that we want to solve Ax=b, ...
- 133
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Remove cycles from a stochastic comparison matrix, while doing the least amount of editing
Let $\mathcal P_n$ be the collection of all matrices $M \in [0, 1]^{n \times n}$ such that $M_{ij} + M_{ji} = 1$ for all $i, j \in [n]$. Such matrices are called comparison matrices. A comparison ...
- 291
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251
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Reference for computing the rank of a matrix in polynomial time
In a recent paper, I need to use the fact that computing the rank of a matrix over the integers has polynomial complexity. Given the context, I don't particularly care about the exact asymptotics, as ...
- 171
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461
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In an $m$ by $n$ Boolean matrix, can you find a square block whose four corners are ones in $O(m \cdot n)$ time?
Decision Problem
Input: An $m$ by $n$ Boolean matrix $M$.
Decision Question: Does there exist a square block within $M$ such that upper-left corner entry == upper-right corner entry == lower-left ...
- 5,127
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175
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Compiling einstein sums optimally
Einstein summation is a convenient way to express tensor operations which has found its way in tensor libraries like numpy, torch, tensorflow, etc.
Its flexibility lets us represent the product of ...
- 419
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147
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Dynamic matrix-matrix multiplication
Suppose A and B are initial Boolean matrices. Let C = A*B. Suppose one can perform the sequence of the next operations: "set A[i,j] = 1", "set B[i,j] = 1". The result of each ...
- 421
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Is there a fast algorithm for computing the Schmidt decomposition
I have a huge covariance matrix, 𝑀, with the dimension, e.g., $10^8 \times 10^8$. Luckily enough, the number of nonzero eigenpairs, $n$, is very small, i.e., $n<5$. From the computational ...
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Finding a non-negative solution to an integer system of linear equations
Let $A$ be an $n \times m$ integer matrix and consider the system of equations $Ax = b$ where $b$ is an integer vector. I want to find a solution $x$, assuming one exists, such that the components of $...
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1k
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Time complexity for multiplying two lower triangular matrices
I was wondering, if multiplication of two $n \times n$ lower (or upper) triangular matrices has a more efficient algorithm than multiplication of two general $n \times n$ matrices?
$$
\begin{bmatrix}
...
- 141
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513
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Distinguish Graph from Tree using Adjacency Matrix
Given an adjacency matrix, is there a way to determine if the graph will be a tree or a graph (whether or not there is a cycle).
For example, given the adjacency matrix:
...
- 1
10
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252
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The complexity of the permanent of low rank matrices
I know that for an arbitrary $n \times n$ matrix, Ryser's algorithm can compute the permanent in $\mathcal{O}(2^n n^2)$ time. I'm interested in computing the permanent of $n \times n$ matrices of rank ...
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Evidence that matrix multiplication is not in $O(n^2\log^kn)$ time
It is commonly believed that for all $\epsilon > 0$, it is possible to multiply two $n \times n$ matrices in $O(n^{2 + \epsilon})$ time. Some discussion is here.
I have asked some people who are ...
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Question about two matrices: Hadamard v. "the magical one" in the proof of the sensitivity conjecture
The recent and incredibly slick proof of the sensitivity conjecture relies on the explicit* construction of a matrix $A_n\in\{-1,0,1\}^{2^n\times 2^n}$, defined recursively as follows:
$$A_1 = \begin{...
- 4,451
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Minimize The Number of Connected Components in Hit-map of A Boolean Matrix
Suppose there is a matrix with the value of 0 and 1. The hit-map of the matrix (0 is blue and 1 is red) create some connected component (see the following figure as an instance):
Is there any ...
- 189
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Complexity of low-rank matrix factorizations with rows in a simplex and outliers
Our goal is to obtain a matrix factorization in form of $M = U V'$, where $U\in\mathbb{R}^{d\times r}, V \in\mathbb{R}^{N\times r}$ and each row of $V$ satisfies
$$ \sum_{j}(V)_{ij}=1, (V)_{ij}\ge 0 $$...
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Ordering of sub problems in dynamic programming
1) Can every dynamic programming question be solved using 3 different orderings or can there be more than 3 or less than 3 ( like unique ordering )?
My understanding is that a) it might have a unique ...
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162
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research problem for undergraduate majoring in Computer Science and Mathematics
I am wondering if somebody can suggest a small research problem for undergraduate majoring in Computer Science and Mathematics. Would love to work with random matrices or wavelets.
- 141
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Finding a Minimal k-Subgraph
Given a complete, positively weighted, bidirectional graph with $n$ nodes without self-loops. Hence the corresponding adjacency matrix $A$ is positive, symmetric, and has zero main diagonal. I am ...
- 129
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Open/unsolved problems in (computational) random matrix theory / matrix completion?
I was wondering what some open problems are in random matrix theory (especially those of interest to TCS people/so mainly non-asymptotic things, I imagine). Also, and relatedly, what are remaining/...
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Efficient Online Algorithms for Matrix rank
Suppose, we have a matrix with known rank. Then, in each step one element of this matrix will be changed. Is there any efficient online algorithm to find rank of each matrix after each element update?
- 189
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Algebraic account of Gaussian elimination?
For fun, I've been looking at the interpretation of linear logic in terms of finite-dimensional vector spaces, and ran into an interesting
question about the interpretation of double-negation-...
- 32.4k
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Decomposing outer product or general rank factorization over $\Bbb F_q$
Given matrix $M\in\Bbb F_q^{n\times n}$ with the promise that there are two matrices $A\in\Bbb F_q^{n\times 1}$ and $B\in\Bbb F_q^{1\times n}$ such that $AB=M$ is there a deterministic $O((n\log q)^c)$...
- 12.8k
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Connection between diamond norm and output purity norm
Setting of the problem: Given a quantum channel $\mathcal{E}: \mathcal{H}_A\rightarrow \mathcal{H}_B$ (where $\mathcal{H}$ refers to a Hilbert space and subscript refers to the quantum register ...
- 253
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On permanent mod $3^t$ computation
By $'$ I mean transpose. I gather the info here from rjlipton.wordpress.com/2014/12/21/modulating-the-permanent.
We know that if $U\in\Bbb F_{3^t}^{n\times n}$ satisfies $UU'=I_n$ in $\Bbb F_{3^t}$ ...
- 12.8k
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Complexity of $\{0,\pm1\}$ determinant in sparse cases?
If $M\in\{-1,0,+1\}^{n\times n}$ be a matrix with only $O(n)$ non-zero entries and hadamard product $M\odot M$ being symmetric can we compute $Det(M)$ in $O(n)$ bit complexity?
Assume that the matrix ...
- 12.8k
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Is there any algorithm to find just the largest eigenvalue with subquadratic time complexity?
SVD or PCA can be used find the largest eigenvalue, but at a cost of $O(n^3)$ complexity. Lanczos algorithm runs much faster on a sparse matrix with complexity $O(dn^2)$ where $d$ is the average ...
- 131
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Rank mod 6 vs rank over the reals
Let $A$ be a boolean matrix (eg with $0,1$ entries). Assume that $A$ has rank $\le r$ both over $\mathbb{F}_2$ and over $\mathbb{F}_3$. Does this imply that $A$ has low rank over the reals? This seems ...
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What's the complexity of factoring over a set of generators (say in $GL_2$)?
In particular, if I have some char-0 field $k$ (let's take $\mathbb C$ for now) and I consider $G = GL_2(k)$ with arbitrary nontrivial distinct $A, B \in G$. Then for some $C \in GL_2(k)$ do we know ...
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Using an oracle to find a vector $b$ for which $Ax=b$ has a solution
There is an oracle built around a hidden $m\times n$ matrix $A$ all of whose entries are 0 or 1, where $m>n$. The oracle takes as input an integer vector $b$ with positive entries, and answers as ...
- 233
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On permanent of $\{\pm1,0\}$ matrices
Consider the problem of computing the permanent $Per(M)$ of a matrix $M\in\{0,-1,1\}^{n\times n}$ such that the result is bounded in absolute value, $|Per(M)|<B$ where $B$ is part of input.
Is ...
- 12.8k
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Properties of convex polytope of 0-1 matrices
Problem setting
Consider a set $ S = \big\{ 1,2,\cdots,n \big\}$. Now consider $k$ equal-sized subsets $S_i \subset S$ s.t of size $\big|S_i\big|=n' \;\forall i$.
Consider a $k\times k$ matrix $M$ ...
- 771
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Complexity involving connected components of 0/1 matrix
Assume a matrix has one component means we can traverse from a matrix entry $(i,j)$ which is $1$ to any other one by moving step of $(i\pm1,j),(i,j\pm1),(i\pm1,j\pm1)$ where each step you take you ...
- 12.8k
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reference request- property of subset of rows in a matrix
I am interested in the following quantity. Suppose we are given a matrix $M\in \mathbb{F}_2^{m\times n}$ and a string $z\in \{0,1\}^n$. I am interested in finding the largest subset $S$ of rows in M ...
- 11
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1
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115
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Low-depth arithmetic complexity of the product of $k$ matrices
Is anything known about the size of $\Sigma\Pi\Sigma$ (or other constant depth) circuits for the product of $k$ matrices?
Trivial upper bounds (up to small factors) are:
if $k=2$, then there are $\...
- 891
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3
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240
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Canonisation of boolean matrices under row and column permutations
Consider the equivalence relation $\sim$ on boolean matrices $A,B\in\{0,1\}^{m\times n}$ which is defined as follows:
$A\sim B$ :iff there are permutation matrices $P\in\{0,1\}^{n\times n}, Q\in\{0,1\...
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0
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145
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On FFT and trigonometric matrix eigenvalues
Let $N=2^n$ for a natural number $n$ and $B$ be the $N\times N$ square matrix of $0$'s and $1$'s
$$
B=\begin{pmatrix}
0 & 1 & 0 & \ldots & 0 \\
1 & 0 & 1 & \ldots ...
- 71