Counting Hierarchies: Polynomial Time and Constant Depth Circuits
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Computational Complexity: a Modern Approach
i Computational Complexity: A Modern Approach Draft of a book: Dated January 2007 Comments welcome! Sanjeev Arora and Boaz Barak Princeton University [email protected] Not to be reproduced or distributed without the authors’ permission This is an Internet draft. Some chapters are more finished than others. References and attributions are very preliminary and we apologize in advance for any omissions (but hope you will nevertheless point them out to us). Please send us bugs, typos, missing references or general comments to [email protected] — Thank You!! DRAFT ii DRAFT Chapter 9 Complexity of counting “It is an empirical fact that for many combinatorial problems the detection of the existence of a solution is easy, yet no computationally efficient method is known for counting their number.... for a variety of problems this phenomenon can be explained.” L. Valiant 1979 The class NP captures the difficulty of finding certificates. However, in many contexts, one is interested not just in a single certificate, but actually counting the number of certificates. This chapter studies #P, (pronounced “sharp p”), a complexity class that captures this notion. Counting problems arise in diverse fields, often in situations having to do with estimations of probability. Examples include statistical estimation, statistical physics, network design, and more. Counting problems are also studied in a field of mathematics called enumerative combinatorics, which tries to obtain closed-form mathematical expressions for counting problems. To give an example, in the 19th century Kirchoff showed how to count the number of spanning trees in a graph using a simple determinant computation. Results in this chapter will show that for many natural counting problems, such efficiently computable expressions are unlikely to exist. -
The Complexity Zoo
The Complexity Zoo Scott Aaronson www.ScottAaronson.com LATEX Translation by Chris Bourke [email protected] 417 classes and counting 1 Contents 1 About This Document 3 2 Introductory Essay 4 2.1 Recommended Further Reading ......................... 4 2.2 Other Theory Compendia ............................ 5 2.3 Errors? ....................................... 5 3 Pronunciation Guide 6 4 Complexity Classes 10 5 Special Zoo Exhibit: Classes of Quantum States and Probability Distribu- tions 110 6 Acknowledgements 116 7 Bibliography 117 2 1 About This Document What is this? Well its a PDF version of the website www.ComplexityZoo.com typeset in LATEX using the complexity package. Well, what’s that? The original Complexity Zoo is a website created by Scott Aaronson which contains a (more or less) comprehensive list of Complexity Classes studied in the area of theoretical computer science known as Computa- tional Complexity. I took on the (mostly painless, thank god for regular expressions) task of translating the Zoo’s HTML code to LATEX for two reasons. First, as a regular Zoo patron, I thought, “what better way to honor such an endeavor than to spruce up the cages a bit and typeset them all in beautiful LATEX.” Second, I thought it would be a perfect project to develop complexity, a LATEX pack- age I’ve created that defines commands to typeset (almost) all of the complexity classes you’ll find here (along with some handy options that allow you to conveniently change the fonts with a single option parameters). To get the package, visit my own home page at http://www.cse.unl.edu/~cbourke/. -
Zero Knowledge and Circuit Minimization
Electronic Colloquium on Computational Complexity, Revision 1 of Report No. 68 (2014) Zero Knowledge and Circuit Minimization Eric Allender1 and Bireswar Das2 1 Department of Computer Science, Rutgers University, USA [email protected] 2 IIT Gandhinagar, India [email protected] Abstract. We show that every problem in the complexity class SZK (Statistical Zero Knowledge) is efficiently reducible to the Minimum Circuit Size Problem (MCSP). In particular Graph Isomorphism lies in RPMCSP. This is the first theorem relating the computational power of Graph Isomorphism and MCSP, despite the long history these problems share, as candidate NP-intermediate problems. 1 Introduction For as long as there has been a theory of NP-completeness, there have been attempts to understand the computational complexity of the following two problems: – Graph Isomorphism (GI): Given two graphs G and H, determine if there is permutation τ of the vertices of G such that τ(G) = H. – The Minimum Circuit Size Problem (MCSP): Given a number i and a Boolean function f on n variables, represented by its truth table of size 2n, determine if f has a circuit of size i. (There are different versions of this problem depending on precisely what measure of “size” one uses (such as counting the number of gates or the number of wires) and on the types of gates that are allowed, etc. For the purposes of this paper, any reasonable choice can be used.) Cook [Coo71] explicitly considered the graph isomorphism problem and mentioned that he “had not been able” to show that GI is NP-complete. -
The Computational Complexity Column by V
The Computational Complexity Column by V. Arvind Institute of Mathematical Sciences, CIT Campus, Taramani Chennai 600113, India [email protected] http://www.imsc.res.in/~arvind The mid-1960’s to the early 1980’s marked the early epoch in the field of com- putational complexity. Several ideas and research directions which shaped the field at that time originated in recursive function theory. Some of these made a lasting impact and still have interesting open questions. The notion of lowness for complexity classes is a prominent example. Uwe Schöning was the first to study lowness for complexity classes and proved some striking results. The present article by Johannes Köbler and Jacobo Torán, written on the occasion of Uwe Schöning’s soon-to-come 60th birthday, is a nice introductory survey on this intriguing topic. It explains how lowness gives a unifying perspective on many complexity results, especially about problems that are of intermediate complexity. The survey also points to the several questions that still remain open. Lowness results: the next generation Johannes Köbler Humboldt Universität zu Berlin [email protected] Jacobo Torán Universität Ulm [email protected] Abstract Our colleague and friend Uwe Schöning, who has helped to shape the area of Complexity Theory in many decisive ways is turning 60 this year. As a little birthday present we survey in this column some of the newer results related with the concept of lowness, an idea that Uwe translated from the area of Recursion Theory in the early eighties. Originally this concept was applied to the complexity classes in the polynomial time hierarchy. -
Is It Easier to Prove Theorems That Are Guaranteed to Be True?
Is it Easier to Prove Theorems that are Guaranteed to be True? Rafael Pass∗ Muthuramakrishnan Venkitasubramaniamy Cornell Tech University of Rochester [email protected] [email protected] April 15, 2020 Abstract Consider the following two fundamental open problems in complexity theory: • Does a hard-on-average language in NP imply the existence of one-way functions? • Does a hard-on-average language in NP imply a hard-on-average problem in TFNP (i.e., the class of total NP search problem)? Our main result is that the answer to (at least) one of these questions is yes. Both one-way functions and problems in TFNP can be interpreted as promise-true distri- butional NP search problems|namely, distributional search problems where the sampler only samples true statements. As a direct corollary of the above result, we thus get that the existence of a hard-on-average distributional NP search problem implies a hard-on-average promise-true distributional NP search problem. In other words, It is no easier to find witnesses (a.k.a. proofs) for efficiently-sampled statements (theorems) that are guaranteed to be true. This result follows from a more general study of interactive puzzles|a generalization of average-case hardness in NP|and in particular, a novel round-collapse theorem for computationally- sound protocols, analogous to Babai-Moran's celebrated round-collapse theorem for information- theoretically sound protocols. As another consequence of this treatment, we show that the existence of O(1)-round public-coin non-trivial arguments (i.e., argument systems that are not proofs) imply the existence of a hard-on-average problem in NP=poly. -
Physics 212B, Ken Intriligator Lecture 6, Jan 29, 2018 • Parity P Acts As P
Physics 212b, Ken Intriligator lecture 6, Jan 29, 2018 Parity P acts as P = P † = P −1 with P~vP = ~v and P~aP = ~a for vectors (e.g. ~x • − and ~p) and axial pseudo-vectors (e.g. L~ and B~ ) respectively. Note that it is not a rotation. Parity preserves all the basic commutation relations, but it is not necessarily a symmetry of the Hamiltonian. The names scalar and pseudo scalar are often used to denote parity even vs odd: P P = for “scalar” operators (like ~x2 or L~ 2, and P ′P = ′ for pseudo O O O −O scalar operators (like S~ ~x). · Nature respects parity aside from some tiny effects at the fundamental level. E.g. • in electricity and magnetism, we can preserve Maxwell’s equations via V~ ~ V and → − V~ +V~ . axial → axial In QM, parity is represented by a unitary operator such that P ~r = ~r and • | i | − i P 2 = 1. So the eigenvectors of P have eigenvalue 1. A state is even or odd under parity ± if P ψ = ψ ; in position space, ψ( ~x) = ψ(~x). In radial coordinates, parity takes | i ±| i − ± cos θ cos θ and φ φ + π, so P α,ℓ,m =( 1)ℓ α,ℓ,m . This is clear also from the → − → | i − | i ℓ = 1 case, any getting general ℓ from tensor products. If [H,P ] = 0, then the non-degenerate energy eigenstates can be written as P eigen- states. Parity in 1d: PxP = x and P pP = p. The Hamiltonian respects parity if V ( x) = − − − V (x). -
The Complexity of Nash Equilibria by Constantinos Daskalakis Diploma
The Complexity of Nash Equilibria by Constantinos Daskalakis Diploma (National Technical University of Athens) 2004 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Computer Science in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Christos H. Papadimitriou, Chair Professor Alistair J. Sinclair Professor Satish Rao Professor Ilan Adler Fall 2008 The dissertation of Constantinos Daskalakis is approved: Chair Date Date Date Date University of California, Berkeley Fall 2008 The Complexity of Nash Equilibria Copyright 2008 by Constantinos Daskalakis Abstract The Complexity of Nash Equilibria by Constantinos Daskalakis Doctor of Philosophy in Computer Science University of California, Berkeley Professor Christos H. Papadimitriou, Chair The Internet owes much of its complexity to the large number of entities that run it and use it. These entities have different and potentially conflicting interests, so their interactions are strategic in nature. Therefore, to understand these interactions, concepts from Economics and, most importantly, Game Theory are necessary. An important such concept is the notion of Nash equilibrium, which provides us with a rigorous way of predicting the behavior of strategic agents in situations of conflict. But the credibility of the Nash equilibrium as a framework for behavior-prediction depends on whether such equilibria are efficiently computable. After all, why should we expect a group of rational agents to behave in a fashion that requires exponential time to be computed? Motivated by this question, we study the computational complexity of the Nash equilibrium. We show that computing a Nash equilibrium is an intractable problem. -
Constructive Galois Connections
ZU064-05-FPR main 23 July 2018 12:36 1 Constructive Galois Connections DAVID DARAIS University of Vermont, USA (e-mail: [email protected]) DAVID VAN HORN University of Maryland, College Park, USA (e-mail: [email protected]) Abstract Galois connections are a foundational tool for structuring abstraction in semantics and their use lies at the heart of the theory of abstract interpretation. Yet, mechanization of Galois connections using proof assistants remains limited to restricted modes of use, preventing their general application in mechanized metatheory and certified programming. This paper presents constructive Galois connections, a variant of Galois connections that is effective both on paper and in proof assistants; is complete with respect toa large subset of classical Galois connections; and enables more general reasoning principles, including the “calculational” style advocated by Cousot. To design constructive Galois connections we identify a restricted mode of use of classical ones which is both general and amenable to mechanization in dependently-typed functional programming languages. Crucial to our metatheory is the addition of monadic structure to Galois connections to control a “specification effect.” Effectful calculations may reason classically, while pure calculations have extractable computational content. Explicitly moving between the worlds of specification and implementation is enabled by our metatheory. To validate our approach, we provide two case studies in mechanizing existing proofs from the literature: the first uses calculational abstract interpretation to design a static analyzer; the second forms a semantic basis for gradual typing. Both mechanized proofs closely follow their original paper-and-pencil counterparts, employ reasoning principles arXiv:1807.08711v1 [cs.PL] 23 Jul 2018 not captured by previous mechanization approaches, support the extraction of verified algorithms, and are novel. -
Structure Vs. Hardness Through the Obfuscation Lens∗
Electronic Colloquium on Computational Complexity, Revision 3 of Report No. 91 (2016) Structure vs. Hardness through the Obfuscation Lens∗ Nir Bitansky Akshay Degwekar Vinod Vaikuntanathan Abstract Much of modern cryptography, starting from public-key encryption and going beyond, is based on the hardness of structured (mostly algebraic) problems like factoring, discrete log, or finding short lattice vectors. While structure is perhaps what enables advanced applications, it also puts the hardness of these problems in question. In particular, this structure often puts them in low (and so called structured) complexity classes such as NP \ coNP or statistical zero-knowledge (SZK). Is this structure really necessary? For some cryptographic primitives, such as one-way per- mutations and homomorphic encryption, we know that the answer is yes | they imply hard problems in NP \ coNP and SZK, respectively. In contrast, one-way functions do not imply such hard problems, at least not by black-box reductions. Yet, for many basic primitives such as public-key encryption, oblivious transfer, and functional encryption, we do not have any answer. We show that the above primitives, and many others, do not imply hard problems in NP \ coNP or SZK via black-box reductions. In fact, we first show that even the very powerful notion of Indistinguishability Obfuscation (IO) does not imply such hard problems, and then deduce the same for a large class of primitives that can be constructed from IO. Keywords: Indistinguishability Obfuscation, Statistical Zero-knowledge, NP \ coNP, Struc- tured Hardness, Collision-Resistant Hashing. ∗MIT. E-mail: fnirbitan,akshayd,[email protected]. Research supported in part by NSF Grants CNS- 1350619 and CNS-1414119, Alfred P. -
Models of Parallel Computation and Parallel Complexity
Models of Parallel Computation and Parallel Complexity George Lentaris Q ¹ ¸8 A thesis submitted in partial ful¯lment of the requirements for the degree of Master of Science in Logic, Algorithms and Computation. Department of Mathematics, National & Kapodistrian University of Athens supervised by: Asst. Prof. Dionysios Reisis, NKUA Prof. Stathis Zachos, NTUA Athens, July 2010 Abstract This thesis reviews selected topics from the theory of parallel computa- tion. The research begins with a survey of the proposed models of parallel computation. It examines the characteristics of each model and it discusses its use either for theoretical studies, or for practical applications. Subse- quently, it employs common simulation techniques to evaluate the computa- tional power of these models. The simulations establish certain model rela- tions before advancing to a detailed study of the parallel complexity theory, which is the subject of the second part of this thesis. The second part exam- ines classes of feasible highly parallel problems and it investigates the limits of parallelization. It is concerned with the bene¯ts of the parallel solutions and the extent to which they can be applied to all problems. It analyzes the parallel complexity of various well-known tractable problems and it discusses the automatic parallelization of the e±cient sequential algorithms. Moreover, it compares the models with respect to the cost of realizing parallel solutions. Overall, the thesis presents various class inclusions, problem classi¯cations and open questions of the ¯eld. George Lentaris Committee: Asst. Prof. Dionysios Reisis, Prof. Stathis Zachos, Prof. Vassilis Zissimopoulos, Lect. Aris Pagourtzis. Graduate Program in Logic, Algorithms and Computation Departments of Mathematics, Informatics, M.I.TH.E. -
Zero-Knowledge Interactive Proof Systems for New Lattice Problems
Zero-Knowledge Interactive Proof Systems for New Lattice Problems Claude Cr´epeau? and Raza Ali Kazmi? McGiLL University [email protected], [email protected] Abstract. In this work we introduce a new hard problem in lattices called Isometric Lattice Problem (ILP) and reduce Linear Code Equivalence over prime fields and Graph Isomorphism to this prob- lem. We also show that this problem has an (efficient prover) perfect zero-knowledge interactive proof; this is the only hard problem in lattices that is known to have this property (with respect to malicious verifiers). Under the assumption that the polynomial hierarchy does not collapse, we also show that ILP cannot be NP-complete. We finally introduce a variant of ILP over the rationals radicands and provide similar results for this new problem. 1 Introduction Zero-Knowledge interactive proof systems ZKIP [6] have numerous applications in cryptography such as Identification Schemes, Authentication Schemes, Mul- tiparty Computations, etc. Appart from cryptographic applications these proof systems play an important part in the study of complexity theory. The first IP for lattice problems (coGapCVPγ ; coGapSVPγ ) was presented by Goldreich and Goldwasser [13]. However, these proofs are only honest-verifier Perfect Zero- Knowledge and known to have inefficient provers. Micciancio and Vadhan [10] presented Interactive Proofs for GapCVPγ and GapSVPγ . These proofs are Statistical Zero-Knowledge and have efficient provers1 as well. In this paper we introduce a new hard problem called ISOMETRIC LATTICE PROBLEM (ILP). We present IP systems for the ILP. These proof systems are Perfect Zero-Knowledge and have efficient provers. -
Parity Detection of Propagating Microwave Fields
Parity Detection of Propagating Microwave Fields Jean-Claude Besse,1, ∗ Simone Gasparinetti,1, y Michele C. Collodo,1 Theo Walter,1 Ants Remm,1 Jonas Krause,1 Christopher Eichler,1 and Andreas Wallraff1 1Department of Physics, ETH Zurich, CH-8093 Zurich, Switzerland (Dated: December 23, 2019) The parity of the number of elementary excitations present in a quantum system provides impor- tant insights into its physical properties. Parity measurements are used, for example, to tomographi- cally reconstruct quantum states or to determine if a decay of an excitation has occurred, information which can be used for quantum error correction in computation or communication protocols. Here we demonstrate a versatile parity detector for propagating microwaves, which distinguishes between radiation fields containing an even or odd number n of photons, both in a single-shot measurement and without perturbing the parity of the detected field. We showcase applications of the detector for direct Wigner tomography of propagating microwaves and heralded generation of Schr¨odinger cat states. This parity detection scheme is applicable over a broad frequency range and may prove useful, for example, for heralded or fault-tolerant quantum communication protocols. I. INTRODUCTION qubits for measurement based entanglement generation [13], for elements of error correction [14{16], and entan- In quantum physics, the parity P of a wavefunction glement stabilization [17], an experiment which was also governs whether a system has an even or odd number of performed with ions [18, 19]. excitations n. The parity affects, for example, the sys- tem's statistical properties such as the likelihood of tran- sitions occurring between distinct quantum states [1,2].