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/*
 * 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.analysis.function;

import java.util.Arrays;

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

/**
 * 
 *  Step function.
 *
 * @since 3.0
 */
public class StepFunction implements UnivariateFunction {
    /** Abscissae. */
    private final double[] abscissa;
    /** Ordinates. */
    private final double[] ordinate;

    /**
     * Builds a step function from a list of arguments and the corresponding
     * values. Specifically, returns the function h(x) defined by 

     * h(x) = y[0] for all x < x[1]
     *        y[1] for x[1] ≤ x < x[2]
     *        ...
     *        y[y.length - 1] for x ≥ x[x.length - 1]
     * 
* The value of {@code x[0]} is ignored, but it must be strictly less than * {@code x[1]}. * * @param x Domain values where the function changes value. * @param y Values of the function. * @throws NonMonotonicSequenceException * if the {@code x} array is not sorted in strictly increasing order. * @throws NullArgumentException if {@code x} or {@code y} are {@code null}. * @throws NoDataException if {@code x} or {@code y} are zero-length. * @throws DimensionMismatchException if {@code x} and {@code y} do not * have the same length. */ public StepFunction(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); } /** {@inheritDoc} */ public double value(double x) { int index = Arrays.binarySearch(abscissa, x); double fx = 0; if (index < -1) { // "x" is between "abscissa[-index-2]" and "abscissa[-index-1]". fx = 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; } }




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