001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math3.fitting;
018
019import java.util.Collection;
020
021import org.apache.commons.math3.analysis.polynomials.PolynomialFunction;
022import org.apache.commons.math3.exception.MathInternalError;
023import org.apache.commons.math3.fitting.leastsquares.LeastSquaresBuilder;
024import org.apache.commons.math3.fitting.leastsquares.LeastSquaresProblem;
025import org.apache.commons.math3.linear.DiagonalMatrix;
026
027/**
028 * Fits points to a {@link
029 * org.apache.commons.math3.analysis.polynomials.PolynomialFunction.Parametric polynomial}
030 * function.
031 * <br/>
032 * The size of the {@link #withStartPoint(double[]) initial guess} array defines the
033 * degree of the polynomial to be fitted.
034 * They must be sorted in increasing order of the polynomial's degree.
035 * The optimal values of the coefficients will be returned in the same order.
036 *
037 * @since 3.3
038 */
039public class PolynomialCurveFitter extends AbstractCurveFitter {
040    /** Parametric function to be fitted. */
041    private static final PolynomialFunction.Parametric FUNCTION = new PolynomialFunction.Parametric();
042    /** Initial guess. */
043    private final double[] initialGuess;
044    /** Maximum number of iterations of the optimization algorithm. */
045    private final int maxIter;
046
047    /**
048     * Contructor used by the factory methods.
049     *
050     * @param initialGuess Initial guess.
051     * @param maxIter Maximum number of iterations of the optimization algorithm.
052     * @throws MathInternalError if {@code initialGuess} is {@code null}.
053     */
054    private PolynomialCurveFitter(double[] initialGuess,
055                                  int maxIter) {
056        this.initialGuess = initialGuess;
057        this.maxIter = maxIter;
058    }
059
060    /**
061     * Creates a default curve fitter.
062     * Zero will be used as initial guess for the coefficients, and the maximum
063     * number of iterations of the optimization algorithm is set to
064     * {@link Integer#MAX_VALUE}.
065     *
066     * @param degree Degree of the polynomial to be fitted.
067     * @return a curve fitter.
068     *
069     * @see #withStartPoint(double[])
070     * @see #withMaxIterations(int)
071     */
072    public static PolynomialCurveFitter create(int degree) {
073        return new PolynomialCurveFitter(new double[degree + 1], Integer.MAX_VALUE);
074    }
075
076    /**
077     * Configure the start point (initial guess).
078     * @param newStart new start point (initial guess)
079     * @return a new instance.
080     */
081    public PolynomialCurveFitter withStartPoint(double[] newStart) {
082        return new PolynomialCurveFitter(newStart.clone(),
083                                         maxIter);
084    }
085
086    /**
087     * Configure the maximum number of iterations.
088     * @param newMaxIter maximum number of iterations
089     * @return a new instance.
090     */
091    public PolynomialCurveFitter withMaxIterations(int newMaxIter) {
092        return new PolynomialCurveFitter(initialGuess,
093                                         newMaxIter);
094    }
095
096    /** {@inheritDoc} */
097    @Override
098    protected LeastSquaresProblem getProblem(Collection<WeightedObservedPoint> observations) {
099        // Prepare least-squares problem.
100        final int len = observations.size();
101        final double[] target  = new double[len];
102        final double[] weights = new double[len];
103
104        int i = 0;
105        for (WeightedObservedPoint obs : observations) {
106            target[i]  = obs.getY();
107            weights[i] = obs.getWeight();
108            ++i;
109        }
110
111        final AbstractCurveFitter.TheoreticalValuesFunction model =
112                new AbstractCurveFitter.TheoreticalValuesFunction(FUNCTION, observations);
113
114        if (initialGuess == null) {
115            throw new MathInternalError();
116        }
117
118        // Return a new least squares problem set up to fit a polynomial curve to the
119        // observed points.
120        return new LeastSquaresBuilder().
121                maxEvaluations(Integer.MAX_VALUE).
122                maxIterations(maxIter).
123                start(initialGuess).
124                target(target).
125                weight(new DiagonalMatrix(weights)).
126                model(model.getModelFunction(), model.getModelFunctionJacobian()).
127                build();
128
129    }
130
131}