7 research outputs found
Quasipolynomial Hitting Sets for Circuits with Restricted Parse Trees
We study the class of non-commutative Unambiguous circuits or Unique-Parse-Tree (UPT) circuits, and a related model of Few-Parse-Trees (FewPT) circuits (which were recently introduced by Lagarde, Malod and Perifel [Guillaume Lagarde et al., 2016] and Lagarde, Limaye and Srinivasan [Guillaume Lagarde et al., 2017]) and give the following constructions:
- An explicit hitting set of quasipolynomial size for UPT circuits,
- An explicit hitting set of quasipolynomial size for FewPT circuits (circuits with constantly many parse tree shapes),
- An explicit hitting set of polynomial size for UPT circuits (of known parse tree shape), when a parameter of preimage-width is bounded by a constant.
The above three results are extensions of the results of [Manindra Agrawal et al., 2015], [Rohit Gurjar et al., 2015] and [Rohit Gurjar et al., 2016] to the setting of UPT circuits, and hence also generalize their results in the commutative world from read-once oblivious algebraic branching programs (ROABPs) to UPT-set-multilinear circuits.
The main idea is to study shufflings of non-commutative polynomials, which can then be used to prove suitable depth reduction results for UPT circuits and thereby allow a careful translation of the ideas in [Manindra Agrawal et al., 2015], [Rohit Gurjar et al., 2015] and [Rohit Gurjar et al., 2016]
Near-optimal Bootstrapping of Hitting Sets for Algebraic Models
The classical lemma of Ore-DeMillo-Lipton-Schwartz-Zippel
[Ore22,DL78,Zip79,Sch80] states that any nonzero polynomial of degree at most will evaluate to a nonzero value at some point on a
grid with . Thus, there is an explicit
hitting set for all -variate degree , size algebraic circuits of size
.
In this paper, we prove the following results:
- Let be a constant. For a sufficiently large constant and
all , if we have an explicit hitting set of size
for the class of -variate degree polynomials that are computable by
algebraic circuits of size , then for all , we have an explicit hitting
set of size for -variate circuits of
degree and size . That is, if we can obtain a barely non-trivial
exponent compared to the trivial sized hitting set even for
constant variate circuits, we can get an almost complete derandomization of
PIT.
- The above result holds when "circuits" are replaced by "formulas" or
"algebraic branching programs".
This extends a recent surprising result of Agrawal, Ghosh and Saxena [AGS18]
who proved the same conclusion for the class of algebraic circuits, if the
hypothesis provided a hitting set of size at most
(where is any constant). Hence, our work significantly weakens the
hypothesis of Agrawal, Ghosh and Saxena to only require a slightly non-trivial
saving over the trivial hitting set, and also presents the first such result
for algebraic branching programs and formulas.Comment: The main result has been strengthened significantly, compared to the
older version of the paper. Additionally, the stronger theorem now holds even
for subclasses of algebraic circuits, such as algebraic formulas and
algebraic branching program
On Annihilators of Explicit Polynomial Maps
We study the algebraic complexity of annihilators of polynomials maps. In
particular, when a polynomial map is `encoded by' a small algebraic circuit, we
show that the coefficients of an annihilator of the map can be computed in
PSPACE. Even when the underlying field is that of reals or complex numbers, an
analogous statement is true. We achieve this by using the class VPSPACE that
coincides with computability of coefficients in PSPACE, over integers.
As a consequence, we derive the following two conditional results. First, we
show that a VP-explicit hitting set generator for all of VP would separate
either VP from VNP, or non-uniform P from PSPACE. Second, in relation to
algebraic natural proofs, we show that proving an algebraic natural proofs
barrier would imply either VP VNP or DSPACE()
P
On Finer Separations Between Subclasses of Read-Once Oblivious ABPs
Read-once Oblivious Algebraic Branching Programs (ROABPs) compute polynomials
as products of univariate polynomials that have matrices as coefficients. In an
attempt to understand the landscape of algebraic complexity classes surrounding
ROABPs, we study classes of ROABPs based on the algebraic structure of these
coefficient matrices. We study connections between polynomials computed by
these structured variants of ROABPs and other well-known classes of polynomials
(such as depth-three powering circuits, tensor-rank and Waring rank of
polynomials).
Our main result concerns commutative ROABPs, where all coefficient matrices
commute with each other, and diagonal ROABPs, where all the coefficient
matrices are just diagonal matrices. In particular, we show a somewhat
surprising connection between these models and the model of depth-three
powering circuits that is related to the Waring rank of polynomials. We show
that if the dimension of partial derivatives captures Waring rank up to
polynomial factors, then the model of diagonal ROABPs efficiently simulates the
seemingly more expressive model of commutative ROABPs. Further, a commutative
ROABP that cannot be efficiently simulated by a diagonal ROABP will give an
explicit polynomial that gives a super-polynomial separation between dimension
of partial derivatives and Waring rank.
Our proof of the above result builds on the results of Marinari, M\"oller and
Mora (1993), and M\"oller and Stetter (1995), that characterise rings of
commuting matrices in terms of polynomials that have small dimension of partial
derivatives. The algebraic structure of the coefficient matrices of these
ROABPs plays a crucial role in our proofs.Comment: Accepted to STACS 202
If VNP Is Hard, Then so Are Equations for It
Assuming that the Permanent polynomial requires algebraic circuits of exponential size, we show that the class VNP does not have efficiently computable equations. In other words, any nonzero polynomial that vanishes on the coefficient vectors of all polynomials in the class VNP requires algebraic circuits of super-polynomial size.
In a recent work of Chatterjee, Kumar, Ramya, Saptharishi and Tengse (FOCS 2020), it was shown that the subclasses of VP and VNP consisting of polynomials with bounded integer coefficients do have equations with small algebraic circuits. Their work left open the possibility that these results could perhaps be extended to all of VP or VNP. The results in this paper show that assuming the hardness of Permanent, at least for VNP, allowing polynomials with large coefficients does indeed incur a significant blow up in the circuit complexity of equations
Monotone Classes Beyond VNP
We study the natural monotone analogues of various equivalent definitions of
VPSPACE: a well studied class (Poizat '08, Koiran-Perifel '09, Malod '11,
Mahajan-Rao '13) that is believed to be larger than VNP. We show an exponential
separation between the monotone version of Poizat's definition, and monotone
VNP. We also show that unlike their non-monotone counterparts, these monotone
analogues are not equivalent, with exponential separations in some cases.
The primary motivation behind our work is to understand the monotone
complexity of transparent polynomials, a concept that was recently introduced
by Hrube\v{s} and Yehudayoff (2021). In that context, we are able to show that
transparent polynomials of large sparsity are hard for the monotone analogues
of all known definitions of VPSPACE, except for the one due to Poizat.Comment: 26 pages; the draft has been shortened and simplified to now focus
solely on monotone classes beyond VN