Forbes, Michael A. ;
Shpilka, Amir ;
Tzameret, Iddo ;
Wigderson, Avi
Proof Complexity Lower Bounds from Algebraic Circuit Complexity
Abstract
We give upper and lower bounds on the power of subsystems of the Ideal Proof System (IPS), the algebraic proof system recently proposed by Grochow and Pitassi, where the circuits comprising the proof come from various restricted algebraic circuit classes. This mimics an established research direction in the boolean setting for subsystems of Extended Frege proofs whose lines are circuits from restricted boolean circuit classes. Essentially all of the subsystems considered in this paper can simulate the wellstudied Nullstellensatz proof system, and prior to this work there were no known lower bounds when measuring proof size by the algebraic complexity of the polynomials (except with respect to degree, or to sparsity).
Our main contributions are two general methods of converting certain algebraic lower bounds into proof complexity ones. Both require stronger arithmetic lower bounds than common, which should hold not for a specific polynomial but for a whole family defined by it. These may be likened to some of the methods by which Boolean circuit lower bounds are turned into related proofcomplexity ones, especially the "feasible interpolation" technique. We establish algebraic lower bounds of these forms for several explicit polynomials, against a variety of classes, and infer the relevant proof complexity bounds. These yield separations between IPS subsystems, which we complement by simulations to create a partial structure theory for IPS systems.
Our first method is a functional lower bound, a notion of Grigoriev and Razborov, which is a function f' from nbit strings to a field, such that any polynomial f agreeing with f' on the boolean cube requires large algebraic circuit complexity. We develop functional lower bounds for a variety of circuit classes (sparse polynomials, depth3 powering formulas, readonce algebraic branching programs and multilinear formulas) where f'(x) equals 1/p(x) for a constantdegree polynomial p depending on the relevant circuit class. We believe these lower bounds are of independent interest in algebraic complexity, and show that they also imply lower bounds for the size of the corresponding IPS refutations for proving that the relevant polynomial p is nonzero over the boolean cube. In particular, we show superpolynomial lower bounds for refuting variants of the subsetsum axioms in these IPS subsystems.
Our second method is to give lower bounds for multiples, that is, to give explicit polynomials whose all (nonzero) multiples require large algebraic circuit complexity. By extending known techniques, we give lower bounds for multiples for various restricted circuit classes such sparse polynomials, sums of powers of lowdegree polynomials, and roABPs. These results are of independent interest, as we argue that lower bounds for multiples is the correct notion for instantiating the algebraic hardness versus randomness paradigm of Kabanets and Impagliazzo. Further, we show how such lower bounds for multiples extend to lower bounds for refutations in the corresponding IPS subsystem.
BibTeX  Entry
@InProceedings{forbes_et_al:LIPIcs:2016:5832,
author = {Michael A. Forbes and Amir Shpilka and Iddo Tzameret and Avi Wigderson},
title = {{Proof Complexity Lower Bounds from Algebraic Circuit Complexity}},
booktitle = {31st Conference on Computational Complexity (CCC 2016)},
pages = {32:132:17},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {9783959770088},
ISSN = {18688969},
year = {2016},
volume = {50},
editor = {Ran Raz},
publisher = {Schloss DagstuhlLeibnizZentrum fuer Informatik},
address = {Dagstuhl, Germany},
URL = {http://drops.dagstuhl.de/opus/volltexte/2016/5832},
URN = {urn:nbn:de:0030drops58321},
doi = {10.4230/LIPIcs.CCC.2016.32},
annote = {Keywords: Proof Complexity, Algebraic Complexity, Nullstellensatz, SubsetSum}
}
2016
Keywords: 

Proof Complexity, Algebraic Complexity, Nullstellensatz, SubsetSum 
Seminar: 

31st Conference on Computational Complexity (CCC 2016)

Issue date: 

2016 
Date of publication: 

2016 