Advanced Concepts in Computational Theory
Explore the latest research on improved composition theorems for functions and relations, background on Boolean circuits, P vs. NP through circuits, and topics like Karchmer-Wigderson Relation, Communication Complexity, and Circuit complexity. Discover intriguing conjectures, intricate algorithms, and the interplay between different theoretical concepts in computer science.
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Improved Composition Theorems for Functions and Relations Sajin Koroth University of Haifa joint work with Or Meir University of Haifa
Background Boolean circuits Size : number of internal gates Depth : The length of the longest path from root to a leaf ?(?) : minimum depth of any circuit computing ? Circuit computing Parity on 2 bits
P vs NP through circuits P has Poly Size circuits NP is believed not to Unfortunately for ?? : 5 ? 1 ? lower bounds for weaker class of circuits
?? ?? ??1 and ? ?? ??1 ??1 : poly size, ? log ? depth, fan-in 2 ??1 : efficient parallel algorithms Weaker goal : ?? ??1 Belief : ? ??1 explicit function ? in ? with ? ? = ? log ?
Compositions and ? ?? ??1 Karchmer Raz and Wigderson 91 : study composition of functions tostudy depth Given ?:{0,1}? {0,1} and g:{0,1}? {0,1} define ? ? as a function on ?? bits
KRW Conjecture Fact : ? ? ? ? ? + ?(?) KRW Conjecture : ? ? ? ? ? + ?(?) If KRW Conjecture is true : explicit? in ? such that ? ? = (log ?) Implies ? ???
Communication Complexity Relation ? = ?,?,? ? ?,? ?,? ? Alice can t see Bob s input, Bob can t see Alice s input Goal : compute ? s.t., ?,?,? ? Cost of a protocol on (x,y) : The total number of bits Cost of a protocol : worst case over (x,y) For this talk : no randomness CC(R) : Minimum cost of a protocol solving R ? ?
Karchmer Wigderson Relation Let ?:{0,1}? {0,1} ? ? 1(1) ? ? 1(0) Goal : Find an index ? [?] for which ?? ?? Objective : Minimize the total number of bits spoken
Circuit complexity to communication KW 90 : ?? ??? = ?(?) Goal : find ?,?? ?? ? ? 1(1) ? ? 1(0)
KRW conjecture (communication version) ? ? = ??(???) KRW conjecture : ? ? ? ? ? + ?(?) ?? ??? ? ?? ??? + ??(???) KW relation of ? ? :
Simplifying functions Universal relation KRW conjecture implies ? ???and this is a very hard problem KRW suggested a simplification : universal relation Known : ?? ?? = ? Goal : find ?,?? ?? Promise : ? ? ? ? 1(1) ? ? ? 1(0) ?
Composition of Universal Relations Similar to ? ?, but drop ?, drop ? Suggested by KRW 95 : ?? ?? ?? ?? ?? + ?? ?? Promise 1 : ? ? Promise 2 : ?? ?? implies ?? ??
Known results First progress: Edmonds, Impagliazzo, Rudich and Sgall (EIRS) EIRS 91: ?? ?? ?? ? + ? ? The result is for ? = ? ? H stad and Wigderson 90: Alternate proof. Almost tight for ? = ?. HW 90 : ?? ?? ?? 2? 1
Composition of functions with universal relation : ? ?? Gavinsky, Meir, Weinstein and Wigderson (GMWW 14) defined ? ?? for any function ?: 0,1? {0,1} GMWW 14 : study ? ?? as next step between ?? ?? and ? ? GMWW 14 : ?? ? ?? log ? ? + ? ?(? ? log ?) This talk : log ? ? = ?(?)
Outline Our results Proof Overview Highlight of the key ideas of our improvement
Our Lower bounds ?? ? ?? log ? ? + ? ?(log ?) ?? ?? ?? ? + ? ?(log ?) Relation Relation Known Lower bounds Known Lower bounds Trivial Upper Bounds Bounds Trivial Upper Our Lower bound Our Lower bound ? + ? ?( ?) EIRS 91 ? + ? ?( ?) EIRS 91 ? + ? ?(log ?) ? + ? ?(log ?) log ? ? + ? ?(log ?) ?? ?? ?? ?? ? ?? ? + ? ? + ? log ?(?) + ? ? 1 +? log ? ? + ? log ? GMWW 14 ?
Motivation The KRW conjecture implies these conjectures To get ? ??1 from the KRW conjecture : ? ? for arbitrary ?, random ? Close to ? ?? But : need ? = 2 (?) Earlier : significant loss at ? = ?(?2) Detour: Avoiding ? = ?(??): ? ? for random ?, arbitrary ? Problem : Close to ?? ?, don t know lower bounds!
Basic intuition behind the lower bound Proof for ?? ?? Players have to solve ?? on at least one row They need the promise: ?? ?? Need to solve ?? to know for sure ?? ?? Notation : matrix part, vector part of players input
Adversarial Argument Takes protocol solving ?? ?? and produces an error transcript Deterministic protocol
Adversarial Argument for ?? Takes of length ? 2 and produces an error transcript Alice : ?? , Bob : ??, Goal : ? ? s.t. ?? ? (??)? After n-2 steps
High Level Idea Divide communication into two stages First stage : first ? ? bits (? : slack term) Intuition : players ideally solving ?? Second Stage : rest of the communication First stage transcript : ? bits in the second stage
An easy case Input to ?? ?? : ( ?,? , ?,? ). Matrix part : ?,?, vector part : ?,? Players don t speak about matrix part in the first stage They know nothing about any row second stage : at least ? bits (??(??))
Another easy case Players don t speak about vector part in the first stage They haven t solved ??at all #rows with more than ? bit of information < ? ? Make these rows useless. Set ??= ?? second stage : at least ? ? bits (??(??))
Challenging case Players speak about both matrix and column parts in the first stage They haven t solved ?? yet. They don t know any row where ?? ?? Goal : ensure communication about matrix part is wasted Strategy : Classify rows into : revealed and unrevealed Revealed : players spoke more than bits about the row. Unrevealed row : ? ? bits in the second stage For every revealed row : fix ??= ??
Fixing Revealed Rows need to fix ??= ?? for every revealed row Suppose : players learned ? bits about the matrix part Number of revealed rows : ?/? Constraint : #(revealed rows) < ? (? : bits not known about vector part) Lower bound : ? ? + ? ? subject to ? ?< ? First stage: m- ? EIRS : ?, ? = ? = ? ? ?< ?, ? > ? Lower bound : ? ? + ? ? k bits m- ? m-? bits m- ?
Our analysis Main Idea : first stage : communication (matrix part), ? bits + communication (vector part), ? ? ? bits Hence info unknown in vector :? ? + ? Lower bound : ? ? + ? ? subject to ? ?< ? Set ? > 1 ? ?< ? + ?. Hence ? ?< ? is satisfied
A complication first stage : communication (matrix part), ? bits + communication (vector part), ? ? ? bits Fixing ??= ??, could reveal a bit on the matrices Unrevealed row after fixing : ? + ?/? bits Solution : An Iterative Adversary a revealed row,? bits ? ? bits remaining ? ? + 1 bits remaining
Iterative Adversary Potential argument : ? ? ? ? ? # revealed rows, ? ?/(? ?) Choose ? > ?. #bits in unrevealed rows : ?
Thank you Questions ?
