# Tag Info

## Hot answers tagged matrices

### Evidence that matrix multiplication is not in $O(n^2\log^kn)$ time

There's an algorithm for multiplying an $N \times N^{0.172}$ matrix with an $N^{0.172} \times N$ matrix in $N^2 \operatorname{polylog}\left(N\right)$ arithmetic operations. The main identity used for ...
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### Matrix permanent is 0

Expanding my comment: Computing the permanent of a matrix is #P-hard (Valiant 1979) even if the matrix entries are all either 0 or 1. We can interpret a matrix $M \in \{0,1\}^{n \times n}$ as a ...
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### Complexity of k-clique for hypergraphs

It is not known if there is an $\varepsilon > 0$, $c > 2$, and $k > c$ such that $(c,k)$ hyperclique is in $n^{k-\varepsilon}$ time. Note that the case of $k \leq c$ is trivial. For years I ...
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### Evidence that matrix multiplication is not in $O(n^2\log^kn)$ time

Well, one thing is I think that all the constructions we know of - and even the families of potential constructions that people have proposed (e.g., Cohn-Umans approaches, generalizations of ...
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### Finding the sparsest solution to a system of linear equations

Consider the problem $\text{MAX-LIN}(R)$ of maximizing the number of satisfied linear equations over some ring $R$, which is often NP-hard, for example in the case $R=\mathbb{Z}$ Take an instance of ...
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### Approximating the sign rank of a matrix

Recent work by Alon, Moran, and Yehudayoff gives an $O(n/\log n)$ approximation algorithm. Let $d$ be the VC-dimension of a sign matrix $S$. The idea is that there exists an efficiently computable ...

### Complexity of matrix powering

For matrices of sizes $k = 2,3$ the Matrix Powering Positivity Problem is in $\mathsf{P}$ (cf. this paper to appear in STACS 2015)
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### The complexity of the permanent of low rank matrices

The paper "Two algorithmic results for the traveling salesman problem" by Barvinok describes an $n^{\mathcal{O}(m)}$ algorithm for computing the permanent of a rank-m matrix. I don't know whether this ...
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### Exact formula for the number of spanning trees of a rectangle

According to https://www.cse.ust.hk/~golin/pubs/ANALCO_05.pdf there is no closed-form formula known. According to http://arxiv.org/pdf/cond-mat/0004341v1.pdf the number is asymptotic (for $n$ and $m$ ...
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### Matrix vector multiplication algorithm using minimal number of additions

This is essentially the problem that motivated Valiant to introduce matrix rigidity into complexity (as far as I understand the history). A linear circuit is an algebraic circuit whose only gates ...
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### Rate of convergence for the Perron–Frobenius theorem

See the power method for computing eigenvectors: http://en.wikipedia.org/wiki/Power_iteration Convergence is exponential (geometric in the ratio of the top two eigenvalues).
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### Canonisation of boolean matrices under row and column permutations

This problem is precisely the canonization problem for isomorphism of bipartite undirected graphs. While the lexicographically maximum form may be harder, any canonical form will be GI-hard (and so, ...
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### Algebraic account of Gaussian elimination?

You really should read Gowers' essay carefully - it cleanly details the reasons why you need a basis in general. So if there is going to be an algebraic account of Gauss-Jordan, it will necessarily ...
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