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| Content Provider | ACM Digital Library |
|---|---|
| Author | Villa, Tiziano Goldberg, Evguenii I. Carloni, Luca P. Sangiovanni-Vincentelli, Alberto L. Brayton, Robert K. |
| Abstract | We introduce a new technique to solve exactly a discrete optimization problem, based on the paradigm of "negative" thinking. The motivation is that when searching the space of solutions, often a good solution is reached quickly and then improved only a few times before the optimum is found: hence most of the solution space is explored to certify optimality, but it does not yield any improvement of the cost function. So it is quite natural for an algorithm to be "skeptical" about the chance to improve the current best solution. For illustration we have applied our approach to the unate covering problem. We designed a procedure, raiser, implementing a negative thinking search, which is incorporated into a common branch-and-bound procedure. Raiser is invoked at a node of the search tree which is deep enough to justify negative thinking. Raiser tries to detect a hard core of the matrix corresponding to the node by augmenting an independent set of rows in order to increase incrementally the cost of the minimum solutions covering the matrix. Eventually either raiser prunes the subtree rooted at the node (having found a lower bound equal or greater than the current best solution) or returns a new solution that becomes the current best one. Experiments show that our program, aura, outperforms both espresso and our enhancement of espresso using Coudert's limit lower bound. It is always faster and in the most difficult examples either has a running time better by up to two orders of magnitude, or the other programs fail to finish due to timeout or spaceout. The package scherzo is faster on some examples and loses on others, due to a less powerful pruning strategy of the search space, partially mitigated by a more effective computation of the maximal independent set. |
| Starting Page | 91 |
| Ending Page | 98 |
| Page Count | 8 |
| File Format | |
| ISBN | 0818682000 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 1997-11-13 |
| Access Restriction | Subscribed |
| Subject Keyword | Negative thinking covering problem discrete optimization |
| Content Type | Text |
| Resource Type | Article |
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