/*
* 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.NonMonotonicSequenceException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.exception.NoDataException;
import org.apache.commons.math3.util.MathArrays;
/**
* <a href="http://en.wikipedia.org/wiki/Step_function">
* Step function</a>.
*
* @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 <pre><code>
* 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]
* </code></pre>
* 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;
}
}