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Java example source code file (SimplexOptimizer.java)

This example Java source code file (SimplexOptimizer.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

abstractsimplex, baseabstractmultivariateoptimizer, comparator, convergencechecker, deprecated, multivariatefunction, multivariateoptimizer, nullargumentexception, optimizationdata, override, pointvaluepair, simplevaluechecker, simplexoptimizer, suppresswarnings, util

The SimplexOptimizer.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.math3.optimization.direct;

import java.util.Comparator;

import org.apache.commons.math3.analysis.MultivariateFunction;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.optimization.GoalType;
import org.apache.commons.math3.optimization.ConvergenceChecker;
import org.apache.commons.math3.optimization.PointValuePair;
import org.apache.commons.math3.optimization.SimpleValueChecker;
import org.apache.commons.math3.optimization.MultivariateOptimizer;
import org.apache.commons.math3.optimization.OptimizationData;

/**
 * This class implements simplex-based direct search optimization.
 *
 * <p>
 *  Direct search methods only use objective function values, they do
 *  not need derivatives and don't either try to compute approximation
 *  of the derivatives. According to a 1996 paper by Margaret H. Wright
 *  (<a href="http://cm.bell-labs.com/cm/cs/doc/96/4-02.ps.gz">Direct
 *  Search Methods: Once Scorned, Now Respectable</a>), they are used
 *  when either the computation of the derivative is impossible (noisy
 *  functions, unpredictable discontinuities) or difficult (complexity,
 *  computation cost). In the first cases, rather than an optimum, a
 *  <em>not too bad point is desired. In the latter cases, an
 *  optimum is desired but cannot be reasonably found. In all cases
 *  direct search methods can be useful.
 * </p>
 * <p>
 *  Simplex-based direct search methods are based on comparison of
 *  the objective function values at the vertices of a simplex (which is a
 *  set of n+1 points in dimension n) that is updated by the algorithms
 *  steps.
 * <p>
 * <p>
 *  The {@link #setSimplex(AbstractSimplex) setSimplex} method <em>must
 *  be called prior to calling the {@code optimize} method.
 * </p>
 * <p>
 *  Each call to {@link #optimize(int,MultivariateFunction,GoalType,double[])
 *  optimize} will re-use the start configuration of the current simplex and
 *  move it such that its first vertex is at the provided start point of the
 *  optimization. If the {@code optimize} method is called to solve a different
 *  problem and the number of parameters change, the simplex must be
 *  re-initialized to one with the appropriate dimensions.
 * </p>
 * <p>
 *  Convergence is checked by providing the <em>worst points of
 *  previous and current simplex to the convergence checker, not the best
 *  ones.
 * </p>
 * <p>
 * This simplex optimizer implementation does not directly support constrained
 * optimization with simple bounds, so for such optimizations, either a more
 * dedicated method must be used like {@link CMAESOptimizer} or {@link
 * BOBYQAOptimizer}, or the optimized method must be wrapped in an adapter like
 * {@link MultivariateFunctionMappingAdapter} or {@link
 * MultivariateFunctionPenaltyAdapter}.
 * </p>
 *
 * @see AbstractSimplex
 * @see MultivariateFunctionMappingAdapter
 * @see MultivariateFunctionPenaltyAdapter
 * @see CMAESOptimizer
 * @see BOBYQAOptimizer
 * @deprecated As of 3.1 (to be removed in 4.0).
 * @since 3.0
 */
@SuppressWarnings("boxing") // deprecated anyway
@Deprecated
public class SimplexOptimizer
    extends BaseAbstractMultivariateOptimizer<MultivariateFunction>
    implements MultivariateOptimizer {
    /** Simplex. */
    private AbstractSimplex simplex;

    /**
     * Constructor using a default {@link SimpleValueChecker convergence
     * checker}.
     * @deprecated See {@link SimpleValueChecker#SimpleValueChecker()}
     */
    @Deprecated
    public SimplexOptimizer() {
        this(new SimpleValueChecker());
    }

    /**
     * @param checker Convergence checker.
     */
    public SimplexOptimizer(ConvergenceChecker<PointValuePair> checker) {
        super(checker);
    }

    /**
     * @param rel Relative threshold.
     * @param abs Absolute threshold.
     */
    public SimplexOptimizer(double rel, double abs) {
        this(new SimpleValueChecker(rel, abs));
    }

    /**
     * Set the simplex algorithm.
     *
     * @param simplex Simplex.
     * @deprecated As of 3.1. The initial simplex can now be passed as an
     * argument of the {@link #optimize(int,MultivariateFunction,GoalType,OptimizationData[])}
     * method.
     */
    @Deprecated
    public void setSimplex(AbstractSimplex simplex) {
        parseOptimizationData(simplex);
    }

    /**
     * Optimize an objective function.
     *
     * @param maxEval Allowed number of evaluations of the objective function.
     * @param f Objective function.
     * @param goalType Optimization type.
     * @param optData Optimization data. The following data will be looked for:
     * <ul>
     *  <li>{@link org.apache.commons.math3.optimization.InitialGuess InitialGuess}
     *  <li>{@link AbstractSimplex}
     * </ul>
     * @return the point/value pair giving the optimal value for objective
     * function.
     */
    @Override
    protected PointValuePair optimizeInternal(int maxEval, MultivariateFunction f,
                                              GoalType goalType,
                                              OptimizationData... optData) {
        // Scan "optData" for the input specific to this optimizer.
        parseOptimizationData(optData);

        // The parent's method will retrieve the common parameters from
        // "optData" and call "doOptimize".
        return super.optimizeInternal(maxEval, f, goalType, optData);
    }

    /**
     * Scans the list of (required and optional) optimization data that
     * characterize the problem.
     *
     * @param optData Optimization data. The following data will be looked for:
     * <ul>
     *  <li>{@link AbstractSimplex}
     * </ul>
     */
    private void parseOptimizationData(OptimizationData... optData) {
        // The existing values (as set by the previous call) are reused if
        // not provided in the argument list.
        for (OptimizationData data : optData) {
            if (data instanceof AbstractSimplex) {
                simplex = (AbstractSimplex) data;
                continue;
            }
        }
    }

    /** {@inheritDoc} */
    @Override
    protected PointValuePair doOptimize() {
        if (simplex == null) {
            throw new NullArgumentException();
        }

        // Indirect call to "computeObjectiveValue" in order to update the
        // evaluations counter.
        final MultivariateFunction evalFunc
            = new MultivariateFunction() {
                /** {@inheritDoc} */
                public double value(double[] point) {
                    return computeObjectiveValue(point);
                }
            };

        final boolean isMinim = getGoalType() == GoalType.MINIMIZE;
        final Comparator<PointValuePair> comparator
            = new Comparator<PointValuePair>() {
            /** {@inheritDoc} */
            public int compare(final PointValuePair o1,
                               final PointValuePair o2) {
                final double v1 = o1.getValue();
                final double v2 = o2.getValue();
                return isMinim ? Double.compare(v1, v2) : Double.compare(v2, v1);
            }
        };

        // Initialize search.
        simplex.build(getStartPoint());
        simplex.evaluate(evalFunc, comparator);

        PointValuePair[] previous = null;
        int iteration = 0;
        final ConvergenceChecker<PointValuePair> checker = getConvergenceChecker();
        while (true) {
            if (iteration > 0) {
                boolean converged = true;
                for (int i = 0; i < simplex.getSize(); i++) {
                    PointValuePair prev = previous[i];
                    converged = converged &&
                        checker.converged(iteration, prev, simplex.getPoint(i));
                }
                if (converged) {
                    // We have found an optimum.
                    return simplex.getPoint(0);
                }
            }

            // We still need to search.
            previous = simplex.getPoints();
            simplex.iterate(evalFunc, comparator);
            ++iteration;
        }
    }
}

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