ACT Seminar: Dieter van Melkebeek/University of Wisconsin Time Hierarchies for Semantic Models of Computation in TAY 3.128
Speaker Name/Affiliation: Dieter van Melkebeek/Un
iversity of Wisconsin
Talk Title: Time Hierarchies for Semantic Mo
dels of Computation
Date/Time: April 28 2006 at 11:00 a.m.
Coffee: 10:45 a.m.
Location: TAY 3.128
Host: Anna Gal
<
br>Talk Abstract:
A basic question in computational complexity asks whet
her somewhat
more time allows us to solve strictly more decision proble
ms on
a given model of computation. Despite its fundamental nature the
question remains unanswered for many models of interest. Essentially time
hierarchies are known for every syntactic model of computation but open fo
r everything else where we call a model syntactic if there
exists a co
mputable enumeration consisting exactly of the machines
in the model.
There has been significant progress in recent years namely
in es
tablishing time hierarchies for non-syntactic models with
small advice.
In this talk we survey these results and present a generic theorem that c
aptures and strengthens all of them. We show that for virtually any semanti
c model of computation and for any rationals 1 <= c < d there exists a lan
guage computable in time n%5Ed with one bit of advice but not in time n%5Ec
with one bit of advice where we call a model semantic if there exists a c
omputable enumeration that contains all machines in the model but may also
contain others.
Our result implies the first such hierarchy theorem
for
randomized machines with zero-sided error quantum machines with on
e-
or zero-sided error unambiguous machines symmetric alternation Ar
thur-Merlin games of any signature etc. Our argument also yields considera
bly simpler proofs of earlier hierarchy theorems with one bit of advice for
randomized or quantum machines with two-sided error.
This is joint
work with Konstantin Pervyshev.
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