Automatic configuration techniques are widely and successfully used to find good parameter settings for optimization algorithms. Configuration is costly, because it is necessary to evaluate many configurations on diff...
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Automatic configuration techniques are widely and successfully used to find good parameter settings for optimization algorithms. Configuration is costly, because it is necessary to evaluate many configurations on different instances. For decision problems, when the objective is to minimize the running time of the algorithm, many configurators implement capping methods to discard poor configurations early. Such methods are not directly applicable to optimization problems, when the objective is to optimize the cost of the best solution found, given a predefined running time limit. We propose new capping methods for the automatic configuration of optimization algorithms. They use the previous executions to determine a performance envelope, which is used to evaluate new executions and cap those that do not satisfy the envelope conditions. We integrate the capping methods into the irace configurator and evaluate them on different optimization scenarios. Our results show that the proposed methods can save from about 5% to 78% of the configuration effort, while finding configurations of the same quality. Based on the computational analysis, we identify two conservative and two aggressive methods, that save an average of about 20% and 45% of the configuration effort, respectively. We also provide evidence that capping can help to better use the available budget in scenarios with a configuration time limit.
The effect of end conditions and testing procedures on the measured strength of 100- by 200-mm (4- by 8-in.) concrete cylinders were evaluated. Concretes representing three strength levels: 50, 75, and 120 MPa (7000, ...
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The effect of end conditions and testing procedures on the measured strength of 100- by 200-mm (4- by 8-in.) concrete cylinders were evaluated. Concretes representing three strength levels: 50, 75, and 120 MPa (7000, 11 000, and 17 000 psi) were prepared. Cylinder end conditions included grinding and capping with two types of sulfur mortar and cement paste. Effect of thickness of capping material was also evaluated. Cement paste caps produced, on average, 1% higher strengths than ground ends, regardless of concrete strength level and cap thickness. Cylinders capped with sulfur mortar 2 h prior to testing produced 2 to 7% lower strengths than the ground condition. capping cylinders with sulfur mortar seven days prior to testing produced strengths equivalent to the ground condition, except with thick caps of sulfur mortar on the 120 MPa (17 000 psi) concrete, in which case lower strengths were observed. No significant difference between sulfur mortars was evident, even though one was advertised for use with high-strength concrete.
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