de.bund.bfr.math.LinearFunction.java Source code

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Here is the source code for de.bund.bfr.math.LinearFunction.java

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/*******************************************************************************
 * Copyright (c) 2017 German Federal Institute for Risk Assessment (BfR)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Contributors:
 *     Department Biological Safety - BfR
 *******************************************************************************/
package de.bund.bfr.math;

import java.util.Arrays;
import org.apache.commons.math3.analysis.UnivariateFunction;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.NonMonotonicSequenceException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.exception.NoDataException;
import org.apache.commons.math3.util.MathArrays;

public class LinearFunction implements UnivariateFunction {

    private final double[] abscissa;
    private final double[] ordinate;

    public LinearFunction(double[] x, double[] y) throws NullArgumentException, NoDataException,
            DimensionMismatchException, NonMonotonicSequenceException {
        if (x == null || y == null) {
            throw new NullArgumentException();
        }
        if (x.length == 0 || y.length == 0) {
            throw new NoDataException();
        }
        if (y.length != x.length) {
            throw new DimensionMismatchException(y.length, x.length);
        }
        MathArrays.checkOrder(x);

        abscissa = MathArrays.copyOf(x);
        ordinate = MathArrays.copyOf(y);
    }

    @Override
    public double value(double x) {
        int index = Arrays.binarySearch(abscissa, x);
        double fx = 0;

        if (-index - 1 == abscissa.length) {
            // "x" is larger than the last value in "abscissa".
            fx = ordinate[-index - 2];
        } else if (index < -1) {
            // "x" is between "abscissa[-index-2]" and "abscissa[-index-1]".
            double alpha = (x - abscissa[-index - 2]) / (abscissa[-index - 1] - abscissa[-index - 2]);
            fx = alpha * ordinate[-index - 1] + (1 - alpha) * ordinate[-index - 2];
        } else if (index >= 0) {
            // "x" is exactly "abscissa[index]".
            fx = ordinate[index];
        } else {
            // Otherwise, "x" is smaller than the first value in "abscissa"
            // (hence the returned value should be "ordinate[0]").
            fx = ordinate[0];
        }

        return fx;
    }
}