574 research outputs found
Query-to-Communication Lifting for BPP
For any -bit boolean function , we show that the randomized
communication complexity of the composed function , where is an
index gadget, is characterized by the randomized decision tree complexity of
. In particular, this means that many query complexity separations involving
randomized models (e.g., classical vs. quantum) automatically imply analogous
separations in communication complexity.Comment: 21 page
Quadratically Tight Relations for Randomized Query Complexity
Let be a Boolean function. The certificate
complexity is a complexity measure that is quadratically tight for the
zero-error randomized query complexity : . In this paper we study a new complexity measure that we call
expectational certificate complexity , which is also a quadratically
tight bound on : . We prove that and show that there is a quadratic separation between
the two, thus gives a tighter upper bound for . The measure is
also related to the fractional certificate complexity as follows:
. This also connects to an open question by
Aaronson whether is a quadratically tight bound for , as
is in fact a relaxation of .
In the second part of the work, we upper bound the distributed query
complexity for product distributions by the square of
the query corruption bound () which improves upon a
result of Harsha, Jain and Radhakrishnan [2015]. A similar statement for
communication complexity is open.Comment: 14 page
Optimal quantum query bounds for almost all Boolean functions
We show that almost all n-bit Boolean functions have bounded-error quantum
query complexity at least n/2, up to lower-order terms. This improves over an
earlier n/4 lower bound of Ambainis, and shows that van Dam's oracle
interrogation is essentially optimal for almost all functions. Our proof uses
the fact that the acceptance probability of a T-query algorithm can be written
as the sum of squares of degree-T polynomials.Comment: 8 pages LaTe
Low-Sensitivity Functions from Unambiguous Certificates
We provide new query complexity separations against sensitivity for total
Boolean functions: a power separation between deterministic (and even
randomized or quantum) query complexity and sensitivity, and a power
separation between certificate complexity and sensitivity. We get these
separations by using a new connection between sensitivity and a seemingly
unrelated measure called one-sided unambiguous certificate complexity
(). We also show that is lower-bounded by fractional block
sensitivity, which means we cannot use these techniques to get a
super-quadratic separation between and . We also provide a
quadratic separation between the tree-sensitivity and decision tree complexity
of Boolean functions, disproving a conjecture of Gopalan, Servedio, Tal, and
Wigderson (CCC 2016).
Along the way, we give a power separation between certificate
complexity and one-sided unambiguous certificate complexity, improving the
power separation due to G\"o\"os (FOCS 2015). As a consequence, we
obtain an improved lower-bound on the
co-nondeterministic communication complexity of the Clique vs. Independent Set
problem.Comment: 25 pages. This version expands the results and adds Pooya Hatami and
Avishay Tal as author
Optimal Separation and Strong Direct Sum for Randomized Query Complexity
We establish two results regarding the query complexity of bounded-error
randomized algorithms.
* Bounded-error separation theorem. There exists a total function whose -error randomized query complexity
satisfies .
* Strong direct sum theorem. For every function and every , the
randomized query complexity of computing instances of simultaneously
satisfies .
As a consequence of our two main results, we obtain an optimal superlinear
direct-sum-type theorem for randomized query complexity: there exists a
function for which . This answers an open question of Drucker (2012). Combining
this result with the query-to-communication complexity lifting theorem of
G\"o\"os, Pitassi, and Watson (2017), this also shows that there is a total
function whose public-coin randomized communication complexity satisfies
, answering a question of Feder, Kushilevitz,
Naor, and Nisan (1995).Comment: 15 pages, 2 figures, CCC 201
Randomized Query Complexity of Sabotaged and Composed Functions
We study the composition question for bounded-error randomized query complexity: Is R(f circ g) = Omega(R(f)R(g))? We show that inserting a simple function h, whose query complexity is onlyTheta(log R(g)), in between f and g allows us to prove R(f circ h circ g) = Omega(R(f)R(h)R(g)).
We prove this using a new lower bound measure for randomized query complexity we call randomized sabotage complexity, RS(f). Randomized sabotage complexity has several desirable properties, such as a perfect composition theorem, RS(f circ g) >= RS(f) RS(g), and a composition theorem with randomized query complexity, R(f circ g) = Omega(R(f) RS(g)). It is also a quadratically tight lower bound for total functions and can be quadratically superior to the partition bound, the best known general lower bound for randomized query complexity.
Using this technique we also show implications for lifting theorems in communication complexity. We show that a general lifting theorem from zero-error randomized query to communication complexity implies a similar result for bounded-error algorithms for all total functions
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