Questions tagged [linear-algebra]
Linear algebra deals with vector spaces and linear transformations.
227
questions
1
vote
0
answers
52
views
Find linear combination with small support
Let $v_1,\dots,v_n$ be a basis of a vector subspace of $\Bbbk^N$, say for $\Bbbk$ a finite field. I would like an algorithm to find a linear combination of the $v_i$'s with small support, i.e. with ...
- 191
-3
votes
1
answer
96
views
Algebra in complexity theory
Recently an idea came to my mind. Suppose $V$ is vector space and $\dim V = n$. Then, since $V \simeq \mathbb{R}^n$, any conjunction of $n$ boolean formulas $\phi_1, \ldots, \phi_n$ about vectors from ...
- 1
2
votes
0
answers
49
views
Approximate Matrix Multiplication with approximation guarantees that ignore large elements?
Approximate matrix multiplication is a technique to replace a matrix product $A^t B$ with a smaller product $(\Pi A)^t(\Pi B)$.
Intuitively, if $\Pi$ is chosen from a suitable distribution that has
...
- 918
0
votes
1
answer
54
views
Impact HHL caveat relaxation on quantum advantage
We know that there are four caveats for the exponential speedup proven for the HHL algorithm. Could anyone answer how that exponential speedup evolves as we relax the caveats?
For example, the ...
- 1,063
4
votes
1
answer
148
views
On the plausability of quantum RAM
I'm fairly new to quantum computation and quantum complexity theory, but I came across some articles that suggest that quantum RAM (QRAM) is not very realistic assumption. For example some works show ...
- 24.3k
1
vote
0
answers
63
views
Circuit depth of linear algebra operations
I was checking the following paper [1] about low-depth PRFs from lattices. In table 1 on page 4, there is comparison with other constructions, and it shows evaluation depths of certain PRFs. I'm not ...
- 151
0
votes
0
answers
26
views
Linear modular equalities with $0/1$ solution
Let $Ax\equiv b\bmod q$ be a $n\times n$ modular linear system known to have $0/1$ solution where $q$ is a large prime. We can solve in $NC^2$ for general linear systems using determinant and matrix ...
- 12.8k
44
votes
3
answers
6k
views
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 ...
- 36.9k
46
votes
8
answers
21k
views
Complexity of Finding the Eigendecomposition of a Matrix
My question is simple:
What is the worst-case running time of the best known algorithm for computing an eigendecomposition of an $n \times n$ matrix?
Does eigendecomposition reduce to matrix ...
- 121
0
votes
1
answer
199
views
Construction of a collection of subsets of $\{1,2,\ldots,n\}$ with certain properties
Let $n$ be a large positive integer. Given a collection $\mathfrak S$ of subsets of $[n] := \{1,2,\ldots,n\}$, and a vector $z=(z_1,\ldots,z_n)\in \{\pm 1\}^n$, define
$$
f_{\mathfrak S}(z) := \sum_{\...
- 800
3
votes
2
answers
160
views
Worst-case complexity of computing a certain non-standard dot product + algorithms realizing this complexity
Let $n$ be a large positive integer. Give a nonempty collection $\mathcal S$ of subsets of $[n] := \{1,2,\ldots,n\}$, define an inner-product on $\mathbb R^n$ by
\begin{eqnarray}
\langle x,y\rangle_{\...
- 291
3
votes
2
answers
824
views
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
0
votes
1
answer
76
views
An inequality about median of points in higher dimensions
Let $S$ be a set of points in $\mathbf{R^d}$ and let $m$ be the median of this set of points, i.e. $\sum_{x \in S} || x - y||$ is minimized when we have $y=m$. Now let $z$ be an arbitrary point in $\...
- 9,595
4
votes
0
answers
127
views
Boolean matrix $M$ with Boolean rank $r$ but real rank $2^r$
$\newcommand{\F}{\mathbb{F}}\newcommand{\R}{\mathbb{R}}$
Question is in the title basically: does there exist a Boolean matrix $M$ where $\operatorname{rank}_{\F_2}(M)=r$ but $\operatorname{rank}_{\R}(...
- 16.9k
2
votes
2
answers
130
views
Are there publicly available fast Laplacian solvers?
In a much celebrated result, we know that there is a $ O(m\log \frac{1}{\epsilon}) $ time algorithm for solving laplacian systems of the form $Lx=b$ where $L$ is a laplacian of a graph $G$ with $m$ ...
- 1
1
vote
0
answers
26
views
Can input-output matrices optimize bidirectional search?
Given a bidirectional search on a weigthed digraph, could a modified input-output matrix guess what nodes are more likely to belong to the shortest path and the search be done through these nodes ...
3
votes
1
answer
107
views
Strongly polynomial time algorithm for shortest convex combination
Problem: Let $S$ be a finite set of vectors. Let $C$ be their convex hull. Compute $\operatorname{argmin}_{x \in C} \|x\|$.
Reference 1 gives an algorithm for this problem that is finite-time (Section ...
- 6,979
12
votes
2
answers
390
views
On $n$ dimensional manifolds and lattices
I'm looking for the proof of Theorem 4 that appears in this paper:
An Infinite Hierarchy of Intersections of Context-Free Languages by Liu and Weiner.
Theorem 4: An $n$-dimensional affine manifold is ...
- 11.7k
19
votes
1
answer
934
views
Is solving systems of equations modulo $k$ in $\mathsf{coMod}_k\mathsf L$ for $k$ composite?
I'm interested in the complexity of solving linear equations modulo k, for arbitrary k (and with a special interest in prime powers), specifically:
Problem. For a given system of $m$ linear equations ...
- 357
21
votes
1
answer
793
views
What is the most general structure on which matrix product verification can be done in $O(n^2)$ time?
In 1979, Freivalds showed that verifying matrix products over any field can be done in randomized $O(n^2)$ time. More formally, given three matrices A, B, and C, with entries from a field F, the ...
- 357
27
votes
1
answer
439
views
How many multiplications are needed to compute the determinant of a 3×3 matrix?
In a comment on this question in 2016, Jeffrey Shallit remarked:
I've asked experts about this, and apparently it is not even currently known whether or not 9 multiplications are needed to compute ...
- 761
0
votes
1
answer
41
views
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)$...
CommunityBot
- 1
3
votes
1
answer
689
views
Complexity of matrix diagonalization
I'm probably missing a trivial answer, but somehow I can't find it.
Given symmetric matrix $A \in \mathbb R^{n \times n}$, what's the complexity of diagonalizing the matrix, i.e. finding diagonal $\...
- 3,243
6
votes
2
answers
193
views
Reference request for linear algebra over GF(2)
I have been looking for materials on the linear algebra over $GF(2)$ but so far I haven't found any substantial textbooks or notes on this subject. In fact in one of the notes I found the introduction ...
- 4,011
17
votes
2
answers
436
views
similar matrices
Given two $n \times n$ matrices $A$ and $B$, the problem of deciding if there exist a permutation matrix $P$ such that $B = P^{-1}AP$ is equivalent to GI(Graph ...
- 36.9k
3
votes
1
answer
169
views
complexity class of a function - linear combinations and reductions (Fermionant, immanant, $GL_n$ representations)
The fermionant is a matrix function from physics, which is indexed by a positive integer $k$:
\begin{align}
\operatorname{Ferm}_k(A) = \sum_{\lambda} d_{\lambda}^{(k)} \operatorname{Imm}_{\lambda^T}(A)...
- 31
1
vote
0
answers
32
views
Reference showing global optimality of local minima for matrix factorization
Consider the following matrix factorization problem: Given an $n\times m$ matrix M, find $n\times r$ and $m\times r$ matrices $U$ and $V$ such that $||UV^T - M||_F^2$ is minimized.
I have heard it ...
- 111
1
vote
0
answers
69
views
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
1
vote
0
answers
115
views
Is this proof of $LP$ being in $coNP$ correct?
I am referring to the natural decision version of the Linear Programming problem: given $A \in \mathbb{Q}^{m \times n}, \ b \in \mathbb{Q}^m, \ c \in \mathbb{Q}^n, \ \alpha \in \mathbb{Q}$, does there ...
- 89
4
votes
0
answers
68
views
Precise rank of a sparse integer matrix
Consider a large sparse rectangular integer matrix. Is there a way to compute its exact rank that is better in terms of speed and/or memory usage compared to a dense matrix?
2
votes
1
answer
120
views
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), ...
- 11.7k
3
votes
1
answer
234
views
An optimization problem
I am considering the following optimization problem. Let $P$ be a set of $n$ points in $\mathbb{R}^d$
maximize $\sum_{p\in P}\vert\langle \Vert p\Vert p, \hat{x}\rangle\vert$ subject to $\Vert\hat{x}\...
- 136
11
votes
2
answers
4k
views
Complexity of Finding the Eigendecomposition of a *Symmetric* Matrix
This is a specialized version of a previous question:
Complexity of Finding the Eigendecomposition of a Matrix .
For NxN symmetric matrices, it is known that O(N^3) time suffices to compute the ...
- 136
3
votes
1
answer
69
views
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
0
votes
0
answers
25
views
Looking for information about a problem of a least subset of vectors modulo 2 summing to another vector [duplicate]
I'm quite interested in the following algorithmic problem, on which I can't find any information. Phrased as a decision problem:
Given a set of vectors $V$ in $\text{GF}(2)^n$, a vector $\mathbf u$ ...
4
votes
0
answers
112
views
efficiently computing a sum of products of polynomials
Let $F$ be a prime finite field. Let $d$ be a power of two dividing $p-1$. Suppose I have $d$ pairs of univariate polynomials $f_i,g_i$ over $F$ for $i=1,\ldots,d$. All have degree less than $d$.
I ...
- 209
1
vote
0
answers
62
views
Complexity Lower Bounds for 3D Sparse Gaussian Elimination
I'm interested in lower bounds on the complexity in the real-RAM model of solving systems of linear equations which have the sparsity pattern of a three-dimensional cubic mesh. Specifically, consider ...
- 111
2
votes
0
answers
34
views
Complexity of best folding of a 2D set (or how to optimize a sandwich)
Motivation:
I was making lunch for my son, part of which is making a sandwich from two halves of a slice of bread. In order to minimize the parts of bread that have cheese on them, and are not covered ...
- 5,531
1
vote
1
answer
122
views
Linear regression as a hylomorphism
A hylomorphism consists of an anamorphism followed by a catamorphism.
Is it possible to express linear regression as a hylomorphism?
- 32.4k
1
vote
1
answer
212
views
Face-splitting product of two Vandermonde matrices: When is is invertible?
Let $A$ and $B$ be two $n^2 \times n$ Vandermonde matrices with coefficients $\alpha_1,\ldots,\alpha_{n^2}$ and $\beta_1,\ldots,\beta_{n^2}$. Let $M$ be the face-splitting product of $A$ and $B$, that ...
- 800
7
votes
0
answers
254
views
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 ...
- 16.9k
4
votes
0
answers
89
views
Complexity of Encoding a Matroid Flow Problem in a Matrix
Context:
Take a directed graph $G$ with a specified subset of source vertices $S$ and target vertices $T$.
We say a subset $I\subseteq T$ of size $r$ is independent if there exist $r$ distinct ...
- 576
5
votes
1
answer
345
views
When is it hard to invert a sparse matrix?
Are cases where numeric inversion of a sparse matrix is known to be harder than sparse matrix multiplication?
In practice, sparse matrix inversion is done with methods like Jacobi or Gauss-Seidel, ...
- 3,033
1
vote
1
answer
306
views
What is the complexity of this submatrix selection problem?
We have a $kn\times kn$ matrix $M$ made of $n^2$ many $k\times k$ blocks.
We want to find an $n\times n$ submatrix such that each row and column is from distinct window of size $k$ such that the sum ...
- 9,595
97
votes
2
answers
40k
views
What is the actual time complexity of Gaussian elimination?
In an answer to an earlier question, I mentioned the common but false belief that “Gaussian” elimination runs in $O(n^3)$ time. While it is obvious that the algorithm uses $O(n^3)$ arithmetic ...
- 111
1
vote
0
answers
74
views
Computational complexity in linear solvers
I have recently been trying out methods of coding for solving systems of linear equations on Python. Of course, I first used the inbuilt function $\mathit{inv}$ under certain if-conditions to obtain ...
Inershya
6
votes
0
answers
191
views
An optimal subspace projection problem
Suppose we have a $k$-dimensional subspace $V$ in $\mathbb{R}^n$ given by a basis $\{v_1,\cdots,v_k\in \mathbb{R}^n\}$, find an index set $I\subset [n]$ with $|I|=m$ where $k\le m\le n$, such that
$$\...
- 271
-3
votes
1
answer
122
views
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 $...
- 11.7k
16
votes
2
answers
7k
views
What is the fastest algorithm to compute rank of a rectangular matrix?
Given an $m \times n$ matrix (assuming $m \ge n$), what is the fastest algorithm to compute its rank and basis of the columns?
I am aware it can be solved through linear matroid intersection, which ...
- 119
10
votes
1
answer
252
views
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 ...
- 5,772