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/*******************************************************************************
* Copyright (c) 2010-2014, Marton Bur, Balazs Grill, Akos Horvath, Zoltan Ujhelyi, Istvan Rath and Daniel Varro
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package tools.refinery.viatra.runtime.localsearch.planner.cost.impl;
import java.util.Set;
import tools.refinery.viatra.runtime.localsearch.planner.cost.IConstraintEvaluationContext;
import tools.refinery.viatra.runtime.localsearch.planner.cost.ICostFunction;
import tools.refinery.viatra.runtime.matchers.psystem.PConstraint;
import tools.refinery.viatra.runtime.matchers.psystem.PVariable;
import tools.refinery.viatra.runtime.matchers.psystem.basicdeferred.AggregatorConstraint;
import tools.refinery.viatra.runtime.matchers.psystem.basicdeferred.ExportedParameter;
import tools.refinery.viatra.runtime.matchers.psystem.basicdeferred.NegativePatternCall;
import tools.refinery.viatra.runtime.matchers.psystem.basicenumerables.BinaryTransitiveClosure;
import tools.refinery.viatra.runtime.matchers.psystem.basicenumerables.ConstantValue;
/**
* This class can be used to calculate cost of application of a constraint with a given adornment.
*
* For now the logic is based on the following principles:
*
* <li>The transitive closures, NACs and count finds are the most expensive operations
*
* <li>The number of free variables increase the cost
*
* <li>If all the variables of a constraint are free, then its cost equals to twice the number of its parameter
* variables. This solves the problem of unnecessary iteration over instances at the beginning of a plan (thus causing
* very long run times when executing the plan) by applying constraints based on structural features as soon as
* possible.
*
* <br>
*
* @author Marton Bur
* @since 1.4
*
*/
public class VariableBindingBasedCostFunction implements ICostFunction {
// Static cost definitions
private static int MAX = 1000;
private static int exportedParameterCost = MAX - 20;
private static int binaryTransitiveClosureCost = MAX - 50;
private static int nacCost = MAX - 100;
private static int aggregatorCost = MAX - 200;
private static int constantCost = 0;
@Override
public double apply(IConstraintEvaluationContext input) {
PConstraint constraint = input.getConstraint();
Set<PVariable> affectedVariables = constraint.getAffectedVariables();
int cost = 0;
// For constants the cost is determined to be 0.0
// The following constraints should be checks:
// * Binary transitive closure
// * NAC
// * count
// * exported parameter - only a metadata
if (constraint instanceof ConstantValue) {
cost = constantCost;
} else if (constraint instanceof BinaryTransitiveClosure) {
cost = binaryTransitiveClosureCost;
} else if (constraint instanceof NegativePatternCall) {
cost = nacCost;
} else if (constraint instanceof AggregatorConstraint) {
cost = aggregatorCost;
} else if (constraint instanceof ExportedParameter) {
cost = exportedParameterCost;
} else {
// In case of other constraints count the number of unbound variables
for (PVariable pVariable : affectedVariables) {
if (input.getFreeVariables().contains(pVariable)) {
// For each free variable ('without-value-variable') increase cost
cost += 1;
}
}
if (cost == affectedVariables.size()) {
// If all the variables are free, double the cost.
// This ensures that iteration costs more
cost *= 2;
}
}
return Float.valueOf(cost);
}
}
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