70,891 research outputs found
NP-hardness of circuit minimization for multi-output functions
Can we design efficient algorithms for finding fast algorithms? This question is captured by various circuit minimization problems, and algorithms for the corresponding tasks have significant practical applications. Following the work of Cook and Levin in the early 1970s, a central question is whether minimizing the circuit size of an explicitly given function is NP-complete. While this is known to hold in restricted models such as DNFs, making progress with respect to more expressive classes of circuits has been elusive.
In this work, we establish the first NP-hardness result for circuit minimization of total functions in the setting of general (unrestricted) Boolean circuits. More precisely, we show that computing the minimum circuit size of a given multi-output Boolean function f : {0,1}^n ? {0,1}^m is NP-hard under many-one polynomial-time randomized reductions. Our argument builds on a simpler NP-hardness proof for the circuit minimization problem for (single-output) Boolean functions under an extended set of generators.
Complementing these results, we investigate the computational hardness of minimizing communication. We establish that several variants of this problem are NP-hard under deterministic reductions. In particular, unless ? = ??, no polynomial-time computable function can approximate the deterministic two-party communication complexity of a partial Boolean function up to a polynomial. This has consequences for the class of structural results that one might hope to show about the communication complexity of partial functions
'On the Application of Hierarchical Coevolutionary Genetic Algorithms: Recombination and Evaluation Partners'
This paper examines the use of a hierarchical coevolutionary genetic algorithm under different partnering strategies. Cascading clusters of sub-populations are built from the bottom up, with higher-level sub-populations optimising larger parts of the problem. Hence higher-level sub-populations potentially search a larger search space with a lower resolution whilst lower-level sub-populations search a smaller search space with a higher resolution. The effects of different partner selection schemes amongst the sub-populations on solution quality are examined for two constrained optimisation problems. We examine a number of recombination partnering strategies in the construction of higher-level individuals and a number of related schemes for evaluating sub-solutions. It is shown that partnering strategies that exploit problem-specific knowledge are superior and can counter inappropriate (sub-) fitness measurements
Optimum Search Schemes for Approximate String Matching Using Bidirectional FM-Index
Finding approximate occurrences of a pattern in a text using a full-text
index is a central problem in bioinformatics and has been extensively
researched. Bidirectional indices have opened new possibilities in this regard
allowing the search to start from anywhere within the pattern and extend in
both directions. In particular, use of search schemes (partitioning the pattern
and searching the pieces in certain orders with given bounds on errors) can
yield significant speed-ups. However, finding optimal search schemes is a
difficult combinatorial optimization problem.
Here for the first time, we propose a mixed integer program (MIP) capable to
solve this optimization problem for Hamming distance with given number of
pieces. Our experiments show that the optimal search schemes found by our MIP
significantly improve the performance of search in bidirectional FM-index upon
previous ad-hoc solutions. For example, approximate matching of 101-bp Illumina
reads (with two errors) becomes 35 times faster than standard backtracking.
Moreover, despite being performed purely in the index, the running time of
search using our optimal schemes (for up to two errors) is comparable to the
best state-of-the-art aligners, which benefit from combining search in index
with in-text verification using dynamic programming. As a result, we anticipate
a full-fledged aligner that employs an intelligent combination of search in the
bidirectional FM-index using our optimal search schemes and in-text
verification using dynamic programming outperforms today's best aligners. The
development of such an aligner, called FAMOUS (Fast Approximate string Matching
using OptimUm search Schemes), is ongoing as our future work
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