Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Distinguishing secant from cactus varieties   Cactus varieties are a generalization of secant varieties. They are defined
using linear spans of arbitrary finite schemes of bounded length, while secant
varieties use only isolated reduced points. In particular, any secant variety
is always contained in the respective cactus variety, and, except in a few
initial cases, the inclusion is strict. It is known that lots of natural
criteria that test membership in secant varieties are actually only tests for
membership in cactus varieties. In this article, we propose the first
techniques to distinguish actual secant variety from the cactus variety in the
case of the Veronese variety. We focus on two initial cases,
$\kappa_{14}(\nu_d(\mathbb{P}^n))$ and $\kappa_{8,3}(\nu_d(\mathbb{P}^n))$, the
simplest that exhibit the difference between cactus and secant varieties. We
show that for $d\geq 5$, the component of the cactus variety
$\kappa_{14}(\nu_d(\mathbb{P}^6))$ other than the secant variety
$\sigma_{14}(\nu_d(\mathbb{P}^6))$ consists of degree $d$ polynomials divisible
by a $(d-3)$-rd power of a linear form. We generalize this description to an
arbitrary number of variables. We present an algorithm for deciding whether a
point in the cactus variety $\kappa_{14}(\nu_d(\mathbb{P}^n))$ belongs to the
secant variety $\sigma_{14}(\nu_d(\mathbb{P}^n))$ for $d\geq 6,$ $n \geq 6$. We
obtain similar results for the Grassmann cactus variety
$\kappa_{8,3}(\nu_d(\mathbb{P}^n))$. Our intermediate results give also a
partial answer to analogous problems for other cactus varieties and Grassmann
cactus varieties to any Veronese variety.

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The categories of this paper are: hep-th
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: supr-con
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The categories of this paper are: gr-qc
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The categories of this paper are: cs