385 research outputs found
A robust parallel algorithm for combinatorial compressed sensing
In previous work two of the authors have shown that a vector with at most nonzeros can be recovered from an expander
sketch in operations via the
Parallel- decoding algorithm, where denotes the
number of nonzero entries in . In this paper we
present the Robust- decoding algorithm, which robustifies
Parallel- when the sketch is corrupted by additive noise. This
robustness is achieved by approximating the asymptotic posterior distribution
of values in the sketch given its corrupted measurements. We provide analytic
expressions that approximate these posteriors under the assumptions that the
nonzero entries in the signal and the noise are drawn from continuous
distributions. Numerical experiments presented show that Robust- is
superior to existing greedy and combinatorial compressed sensing algorithms in
the presence of small to moderate signal-to-noise ratios in the setting of
Gaussian signals and Gaussian additive noise
Self-Specifying Machines
We study the computational power of machines that specify their own
acceptance types, and show that they accept exactly the languages that
\manyonesharp-reduce to NP sets. A natural variant accepts exactly the
languages that \manyonesharp-reduce to P sets. We show that these two classes
coincide if and only if \psone = \psnnoplusbigohone, where the latter class
denotes the sets acceptable via at most one question to \sharpp followed by
at most a constant number of questions to \np.Comment: 15 pages, to appear in IJFC
Different perceptions of adaptation to climate change: a mental model approach applied to the evidence from expert interviews
We argue that differences in the perception and governance of adaptation to climate change and extreme weather events are related to sets of beliefs and concepts through which people understand the environment and which are used to solve the problems they face (mental models). Using data gathered in 31 in-depth interviews with adaptation experts in Europe, we identify five basic stakeholder groups whose divergent aims and logic can be related to different mental models they use: advocacy groups, administration, politicians, researchers, and media and the public. Each of these groups uses specific interpretations of climate change and specifies how to deal with climate change impacts. We suggest that a deeper understanding and follow-up of the identified mental models might be useful for the design of any stakeholder involvement in future climate impact research processes. It might also foster consensus building about adequate adaptation measures against climate threats in a society
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On the Power of Probabilistic Polynomial Time: PNP[log] ⊆ PP
We show that every set in the ΘP2 level of the polynomial hierarchy -- that is, every set polynomial-time truth-table reducible to SAT -- is accepted by a probabilistic polynomialtime Turing machine: PNP[log] ⊆ PP
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