# Questions tagged [total-positivity]

For questions related to totally positive (or totally nonnegative) matrices, and related topics such as total positivity in a more general Lie-theoretic setting. (Not related to "totally positive integers" in the number-theoretic sense.)

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### The Grassmann twist-map, an associated semi-group action, and RSK

Let me begin by setting some notation: Let $\mathrm{Mat}_{k,n}(\Bbb{R})$ denote the vector space of all $k \times n$ real-valued matrices. Given $g \in \mathrm{Mat}_{k,n}(\Bbb{R})$ and two (ordered) ...
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### Total positivity tests: optimal in the number of minors vs. the computational cost

A real matrix is called totally positive if all of its minors are positive. Of course, to check that a given matrix is totally positive it is not necessary to check all the minors: for example, it ...
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### Embedding of co-oriented subspaces into positive Grassmannian

$\def\R{\mathbb{R}}$Let $P_1$, $P_2$, $P_3$ be three $m$-dimensional subspaces in $\R^n$. With a slight abuse of notation they will also denote the ortho-projectors on the respective subspaces. We ...
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### Positivity of sequences

Totally positive sequences $\lbrace a_n\rbrace_{n\in\mathbb{Z}}$ are defined as those such that the Töplitz matrix $A_{ij}=a_{i-j}$ is totally positive (all its minors are non-negative). An ...
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