gedi.util.math.function.PiecewiseLinearFunction.java Source code

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Here is the source code for gedi.util.math.function.PiecewiseLinearFunction.java

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/**
 * 
 *    Copyright 2017 Florian Erhard
 *
 *   Licensed 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 gedi.util.math.function;

import java.util.Arrays;

import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.NoDataException;
import org.apache.commons.math3.exception.NullArgumentException;

public class PiecewiseLinearFunction extends KnotFunction {

    public PiecewiseLinearFunction(double[] x, double[] y)
            throws NullArgumentException, NoDataException, DimensionMismatchException {
        super(x, y);
    }

    public double applyAsDouble(double x) {
        int index = Arrays.binarySearch(this.x, x);
        double fx = 0;

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

        return fx;
    }

    @Override
    protected double noKnotBetweenintegral(double from, double to) {
        double y1 = applyAsDouble(from);
        double y2 = applyAsDouble(to);

        return (to - from) * Math.min(y1, y2) + 0.5 * (to - from) * Math.abs(y1 - y2);
    }

}