StepFunction.java
- /*
- * 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;
- }
- }