280 research outputs found
Most secant varieties of tangential varieties to Veronese varieties are nondefective
We prove a conjecture stated by Catalisano, Geramita, and Gimigliano in 2002,
which claims that the secant varieties of tangential varieties to the th
Veronese embedding of the projective -space have the expected
dimension, modulo a few well-known exceptions. As Bernardi, Catalisano,
Gimigliano, and Id\'a demonstrated that the proof of this conjecture may be
reduced to the case of cubics, i.e., , the main contribution of this work
is the resolution of this base case. The proposed proof proceeds by induction
on the dimension of the projective space via a specialization argument.
This reduces the proof to a large number of initial cases for the induction,
which were settled using a computer-assisted proof. The individual base cases
were computationally challenging problems. Indeed, the largest base case
required us to deal with the tangential variety to the third Veronese embedding
of in .Comment: 25 pages, 2 figures, extended the introduction, and added a C++ code
as an ancillary fil
Generating Polynomials and Symmetric Tensor Decompositions
This paper studies symmetric tensor decompositions. For symmetric tensors,
there exist linear relations of recursive patterns among their entries. Such a
relation can be represented by a polynomial, which is called a generating
polynomial. The homogenization of a generating polynomial belongs to the apolar
ideal of the tensor. A symmetric tensor decomposition can be determined by a
set of generating polynomials, which can be represented by a matrix. We call it
a generating matrix. Generally, a symmetric tensor decomposition can be
determined by a generating matrix satisfying certain conditions. We
characterize the sets of such generating matrices and investigate their
properties (e.g., the existence, dimensions, nondefectiveness). Using these
properties, we propose methods for computing symmetric tensor decompositions.
Extensive examples are shown to demonstrate the efficiency of proposed methods.Comment: 35 page
Kronecker powers of tensors and Strassen’s laser method
We answer a question, posed implicitly in [18, §11], [11, Rem. 15.44] and explicitly in [9, Problem 9.8], showing the border rank of the Kronecker square of the little Coppersmith-Winograd tensor is the square of the border rank of the tensor for all q > 2, a negative result for complexity theory. We further show that when q > 4, the analogous result holds for the Kronecker cube. In the positive direction, we enlarge the list of explicit tensors potentially useful for the laser method. We observe that a well-known tensor, the 3×3 determinant polynomial regarded as a tensor, det3 ∈ C9 C9 C9, could potentially be used in the laser method to prove the exponent of matrix multiplication is two. Because of this, we prove new upper bounds on its Waring rank and rank (both 18), border rank and Waring border rank (both 17), which, in addition to being promising for the laser method, are of interest in their own right. We discuss “skew” cousins of the little Coppersmith-Winograd tensor and indicate why they may be useful for the laser method. We establish general results regarding border ranks of Kronecker powers of tensors, and make a detailed study of Kronecker squares of tensors in C3 C3 C
Tensor decomposition and homotopy continuation
A computationally challenging classical elimination theory problem is to
compute polynomials which vanish on the set of tensors of a given rank. By
moving away from computing polynomials via elimination theory to computing
pseudowitness sets via numerical elimination theory, we develop computational
methods for computing ranks and border ranks of tensors along with
decompositions. More generally, we present our approach using joins of any
collection of irreducible and nondegenerate projective varieties
defined over . After computing
ranks over , we also explore computing real ranks. Various examples
are included to demonstrate this numerical algebraic geometric approach.Comment: We have added two examples: A Coppersmith-Winograd tensor, Matrix
multiplication with zeros. (26 pages, 1 figure
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