/* * 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.math4.ode; import org.apache.commons.math4.Field; import org.apache.commons.math4.RealFieldElement; import org.apache.commons.math4.util.MathArrays; /** * This class is used in the junit tests for the ODE integrators. * <p>This specific problem is the following differential equation : * <pre> * y' = t^3 - t y * </pre> * with the initial condition y (0) = 0. The solution of this equation * is the following function : * <pre> * y (t) = t^2 + 2 (exp (- t^2 / 2) - 1) * </pre> * </p> * @param <T> the type of the field elements */ public class TestFieldProblem2<T extends RealFieldElement<T>> extends TestFieldProblemAbstract<T> { /** * Simple constructor. * @param field field to which elements belong */ public TestFieldProblem2(Field<T> field) { super(field); setInitialConditions(convert(0.0), convert(new double[] { 0.0 })); setFinalConditions(convert(1.0)); setErrorScale(convert(new double[] { 1.0 })); } @Override public T[] doComputeDerivatives(T t, T[] y) { final T[] yDot = MathArrays.buildArray(getField(), getDimension()); // compute the derivatives for (int i = 0; i < getDimension(); ++i) { yDot[i] = t.multiply(t.multiply(t).subtract(y[i])); } return yDot; } @Override public T[] computeTheoreticalState(T t) { final T[] y = MathArrays.buildArray(getField(), getDimension()); T t2 = t.multiply(t); T c = t2.add(t2.multiply(-0.5).exp().subtract(1).multiply(2)); for (int i = 0; i < getDimension(); ++i) { y[i] = c; } return y; } }