/* * 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;
}
}