1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package org.apache.commons.math4.legacy.ode; 19 20 import org.apache.commons.math4.legacy.core.Field; 21 import org.apache.commons.math4.legacy.core.RealFieldElement; 22 import org.apache.commons.math4.legacy.core.MathArrays; 23 24 /** 25 * This class is used in the junit tests for the ODE integrators. 26 27 * <p>This specific problem is the following differential equation : 28 * <pre> 29 * y' = t^3 - t y 30 * </pre> 31 * with the initial condition y (0) = 0. The solution of this equation 32 * is the following function : 33 * <pre> 34 * y (t) = t^2 + 2 (exp (- t^2 / 2) - 1) 35 * </pre> 36 * </p> 37 38 * @param <T> the type of the field elements 39 */ 40 public class TestFieldProblem2<T extends RealFieldElement<T>> 41 extends TestFieldProblemAbstract<T> { 42 43 /** 44 * Simple constructor. 45 * @param field field to which elements belong 46 */ 47 public TestFieldProblem2(Field<T> field) { 48 super(field); 49 setInitialConditions(convert(0.0), convert(new double[] { 0.0 })); 50 setFinalConditions(convert(1.0)); 51 setErrorScale(convert(new double[] { 1.0 })); 52 } 53 54 @Override 55 public T[] doComputeDerivatives(T t, T[] y) { 56 57 final T[] yDot = MathArrays.buildArray(getField(), getDimension()); 58 // compute the derivatives 59 for (int i = 0; i < getDimension(); ++i) { 60 yDot[i] = t.multiply(t.multiply(t).subtract(y[i])); 61 } 62 63 return yDot; 64 } 65 66 @Override 67 public T[] computeTheoreticalState(T t) { 68 final T[] y = MathArrays.buildArray(getField(), getDimension()); 69 T t2 = t.multiply(t); 70 T c = t2.add(t2.multiply(-0.5).exp().subtract(1).multiply(2)); 71 for (int i = 0; i < getDimension(); ++i) { 72 y[i] = c; 73 } 74 return y; 75 } 76 }