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Java example source code file (CircleScalar.java)

This example Java source code file (CircleScalar.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.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, circlescalar, multivariatefunction, multivariatevectorfunction, objectivefunction, objectivefunctiongradient, util, vector2d

The CircleScalar.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.optim.nonlinear.scalar.gradient;

import java.util.ArrayList;

import org.apache.commons.math3.analysis.MultivariateFunction;
import org.apache.commons.math3.analysis.MultivariateVectorFunction;
import org.apache.commons.math3.geometry.euclidean.twod.Vector2D;
import org.apache.commons.math3.optim.nonlinear.scalar.ObjectiveFunction;
import org.apache.commons.math3.optim.nonlinear.scalar.ObjectiveFunctionGradient;

/**
 * Class used in the tests.
 */
public class CircleScalar {
    private ArrayList<Vector2D> points;

    public CircleScalar() {
        points  = new ArrayList<Vector2D>();
    }

    public void addPoint(double px, double py) {
        points.add(new Vector2D(px, py));
    }

    public double getRadius(Vector2D center) {
        double r = 0;
        for (Vector2D point : points) {
            r += point.distance(center);
        }
        return r / points.size();
    }

    public ObjectiveFunction getObjectiveFunction() {
        return new ObjectiveFunction(new MultivariateFunction() {
                public double value(double[] params)  {
                    Vector2D center = new Vector2D(params[0], params[1]);
                    double radius = getRadius(center);
                    double sum = 0;
                    for (Vector2D point : points) {
                        double di = point.distance(center) - radius;
                        sum += di * di;
                    }
                    return sum;
                }
            });
    }

    public ObjectiveFunctionGradient getObjectiveFunctionGradient() {
        return new ObjectiveFunctionGradient(new MultivariateVectorFunction() {
                public double[] value(double[] params) {
                    Vector2D center = new Vector2D(params[0], params[1]);
                    double radius = getRadius(center);
                    // gradient of the sum of squared residuals
                    double dJdX = 0;
                    double dJdY = 0;
                    for (Vector2D pk : points) {
                        double dk = pk.distance(center);
                        dJdX += (center.getX() - pk.getX()) * (dk - radius) / dk;
                        dJdY += (center.getY() - pk.getY()) * (dk - radius) / dk;
                    }
                    dJdX *= 2;
                    dJdY *= 2;

                    return new double[] { dJdX, dJdY };
                }
            });
    }
}

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