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Java example source code file (CircleProblem.java)

This example Java source code file (CircleProblem.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, circleproblem, deprecated, modelfunction, modelfunctionjacobian, multivariatematrixfunction, multivariatevectorfunction, util

The CircleProblem.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.vector.jacobian;

import java.util.ArrayList;

import org.apache.commons.math3.analysis.MultivariateVectorFunction;
import org.apache.commons.math3.analysis.MultivariateMatrixFunction;
import org.apache.commons.math3.util.MathUtils;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.optim.nonlinear.vector.ModelFunction;
import org.apache.commons.math3.optim.nonlinear.vector.ModelFunctionJacobian;

/**
 * Class that models a circle.
 * The parameters of problem are:
 * <ul>
 *  <li>the x-coordinate of the circle center,
 *  <li>the y-coordinate of the circle center,
 *  <li>the radius of the circle.
 * </ul>
 * The model functions are:
 * <ul>
 *  <li>for each triplet (cx, cy, r), the (x, y) coordinates of a point on the
 *   corresponding circle.</li>
 * </ul>
 */
@Deprecated
class CircleProblem {
    /** Cloud of points assumed to be fitted by a circle. */
    private final ArrayList<double[]> points;
    /** Error on the x-coordinate of the points. */
    private final double xSigma;
    /** Error on the y-coordinate of the points. */
    private final double ySigma;
    /** Number of points on the circumference (when searching which
        model point is closest to a given "observation". */
    private final int resolution;

    /**
     * @param xError Assumed error for the x-coordinate of the circle points.
     * @param yError Assumed error for the y-coordinate of the circle points.
     * @param searchResolution Number of points to try when searching the one
     * that is closest to a given "observed" point.
     */
    public CircleProblem(double xError,
                         double yError,
                         int searchResolution) {
        points = new ArrayList<double[]>();
        xSigma = xError;
        ySigma = yError;
        resolution = searchResolution;
    }

    /**
     * @param xError Assumed error for the x-coordinate of the circle points.
     * @param yError Assumed error for the y-coordinate of the circle points.
     */
    public CircleProblem(double xError,
                         double yError) {
        this(xError, yError, 500);
    }

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

    public double[] target() {
        final double[] t = new double[points.size() * 2];
        for (int i = 0; i < points.size(); i++) {
            final double[] p = points.get(i);
            final int index = i * 2;
            t[index] = p[0];
            t[index + 1] = p[1];
        }

        return t;
    }

    public double[] weight() {
        final double wX = 1 / (xSigma * xSigma);
        final double wY = 1 / (ySigma * ySigma);
        final double[] w = new double[points.size() * 2];
        for (int i = 0; i < points.size(); i++) {
            final int index = i * 2;
            w[index] = wX;
            w[index + 1] = wY;
        }

        return w;
    }

    public ModelFunction getModelFunction() {
        return new ModelFunction(new MultivariateVectorFunction() {
                public double[] value(double[] params) {
                    final double cx = params[0];
                    final double cy = params[1];
                    final double r = params[2];

                    final double[] model = new double[points.size() * 2];

                    final double deltaTheta = MathUtils.TWO_PI / resolution;
                    for (int i = 0; i < points.size(); i++) {
                        final double[] p = points.get(i);
                        final double px = p[0];
                        final double py = p[1];

                        double bestX = 0;
                        double bestY = 0;
                        double dMin = Double.POSITIVE_INFINITY;

                        // Find the angle for which the circle passes closest to the
                        // current point (using a resolution of 100 points along the
                        // circumference).
                        for (double theta = 0; theta <= MathUtils.TWO_PI; theta += deltaTheta) {
                            final double currentX = cx + r * FastMath.cos(theta);
                            final double currentY = cy + r * FastMath.sin(theta);
                            final double dX = currentX - px;
                            final double dY = currentY - py;
                            final double d = dX * dX + dY * dY;
                            if (d < dMin) {
                                dMin = d;
                                bestX = currentX;
                                bestY = currentY;
                            }
                        }

                        final int index = i * 2;
                        model[index] = bestX;
                        model[index + 1] = bestY;
                    }

                    return model;
                }
            });
    }

    public ModelFunctionJacobian getModelFunctionJacobian() {
        return new ModelFunctionJacobian(new MultivariateMatrixFunction() {
                public double[][] value(double[] point) {
                    return jacobian(point);
                }
        });
    }

    private double[][] jacobian(double[] params) {
        final double[][] jacobian = new double[points.size() * 2][3];

        for (int i = 0; i < points.size(); i++) {
            final int index = i * 2;
            // Partial derivative wrt x-coordinate of center.
            jacobian[index][0] = 1;
            jacobian[index + 1][0] = 0;
            // Partial derivative wrt y-coordinate of center.
            jacobian[index][1] = 0;
            jacobian[index + 1][1] = 1;
            // Partial derivative wrt radius.
            final double[] p = points.get(i);
            jacobian[index][2] = (p[0] - params[0]) / params[2];
            jacobian[index + 1][2] = (p[1] - params[1]) / params[2];
        }

        return jacobian;
    }
}

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