Questions tagged [linear-algebra]
Linear algebra deals with vector spaces and linear transformations.
227
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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 ...
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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 ...
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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
...
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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 ...
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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 ...
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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 ...
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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_{\...
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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_{\...
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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 ...
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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 ...
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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 $\...
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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}(...
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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$ ...
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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 ...
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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 ...
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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 ...
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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 $\...
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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 ...
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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)...
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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 ...
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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 $\...
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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 ...
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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
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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), ...
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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, ...
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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$ ...
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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 ...
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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 ...
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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}\...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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
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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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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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Algebraic methods for testing planarity
Mac Lane's planarity criterion states that a graph is planar if and only if it has a cycle basis such that each edge is contained in at most two cycles, we call such a basis a 2-basis. A 2-basis of a ...
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What are some good resources for strengthening my theoretical foundation for machine learning?
I'm a computer science major and I'm taking a lot of machine learning courses. I'm finding that my theoretical foundation on subjects like calculus and linear algebra are not as strong as I'd like ...
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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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Finding whether $n$ polytopes have nontrivial intersection from pairwise comparisons
I have a set of $n$ convex polytopes of the form
$$\mathcal{L_i} = \{ \beta \mid C_i \beta \leq 0 \}$$
where $C$ is a matrix and $\beta$ is a vector. I know that for each pair of polytopes $$(\...
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Underlying codes in Niederreiter cryptosystems
Niederreiter cryptosystem is usually described by a parity check matrix $H$ over $\mathbb{F}_{2^n}$.
The minimum distance $d$ is given by
$d= min\lbrace k \text{ such that there are $k$ linearly ...
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Hardness result or reference for optimal Gaussian elimination process
I'm wondering if the following problem is NP-Complete or has any hardness result.
References on related problem are also welcome.
Input: integers $n\geq1,k\geq0$ and an invertible matrix $M\in\mathbb ...
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Is there a fast algorithm for inverting a sparse matrix?
I am doing research on a random-walk like problem. As a critical part of my solution, I need to invert a non-singular sparse matrix of size $n \times n$ and with $O(n)$ non-empty entries. I'm working ...
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Does optimal fitting flat must pass through the mean of the point set?
I am confused about a statement made in the paper Linear Time Algorithm for Projective Clustering, section 5.1, second paragraph, second line.
Project clustering is a natural generalization of k-...
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Missing proof in Salil Vadhan's monograph on pseudorandomness, Random Walks and S-T Connectivity
In Salil Vadhan's monograph on pseudorandomness, chapter 2, half of the proof of Lemma 2.51 is missing
http://people.seas.harvard.edu/~salil/pseudorandomness/power.pdf .
I don't state the full lemma ...
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Do Banach spaces and linear contraction maps form a model of ILL with an exponential?
Recently, I read on the nLab that the category of Banach spaces and linear contractions is small complete, small cocomplete, and monoidal closed.
This means that Banach spaces and short linear maps ...
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Non-Orthogonal Vectors Problem
Consider the following problems:
Orthogonal Vectors Problem
Input: A set $S$ of $n$ Boolean vectors each of length $d$.
Question: Do there exist distinct vectors $v_1$ and $v_2 \in S$ ...
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