/*
* 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;
/**
* An interface representing a univariate real function.
* <p>
* When a <em>user-defined</em> function encounters an error during
* evaluation, the {@link #value(double) value} method should throw a
* <em>user-defined</em> unchecked exception.</p>
* <p>
* The following code excerpt shows the recommended way to do that using
* a root solver as an example, but the same construct is applicable to
* ODE integrators or optimizers.</p>
*
* <pre>
* private static class LocalException extends RuntimeException {
* // The x value that caused the problem.
* private final double x;
*
* public LocalException(double x) {
* this.x = x;
* }
*
* public double getX() {
* return x;
* }
* }
*
* private static class MyFunction implements UnivariateFunction {
* public double value(double x) {
* double y = hugeFormula(x);
* if (somethingBadHappens) {
* throw new LocalException(x);
* }
* return y;
* }
* }
*
* public void compute() {
* try {
* solver.solve(maxEval, new MyFunction(a, b, c), min, max);
* } catch (LocalException le) {
* // Retrieve the x value.
* }
* }
* </pre>
*
* As shown, the exception is local to the user's code and it is guaranteed
* that Apache Commons Math will not catch it.
*
*/
public interface UnivariateFunction {
/**
* Compute the value of the function.
*
* @param x Point at which the function value should be computed.
* @return the value of the function.
* @throws IllegalArgumentException when the activated method itself can
* ascertain that a precondition, specified in the API expressed at the
* level of the activated method, has been violated.
* When Commons Math throws an {@code IllegalArgumentException}, it is
* usually the consequence of checking the actual parameters passed to
* the method.
*/
double value(double x);
}