| /* |
| * 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.ode; |
| |
| import org.apache.commons.math3.Field; |
| import org.apache.commons.math3.RealFieldElement; |
| import org.apache.commons.math3.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' = -y |
| * </pre> |
| * the solution of this equation is a simple exponential function : |
| * <pre> |
| * y (t) = y (t0) exp (t0-t) |
| * </pre> |
| * </p> |
| |
| * @param <T> the type of the field elements |
| */ |
| public class TestFieldProblem1<T extends RealFieldElement<T>> |
| extends TestFieldProblemAbstract<T> { |
| |
| /** |
| * Simple constructor. |
| * @param field field to which elements belong |
| */ |
| public TestFieldProblem1(Field<T> field) { |
| super(field); |
| setInitialConditions(convert(0.0), convert(1.0, 0.1)); |
| setFinalConditions(convert(4.0)); |
| setErrorScale(convert(1.0, 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] = y[i].negate(); |
| } |
| |
| return yDot; |
| |
| } |
| |
| @Override |
| public T[] computeTheoreticalState(T t) { |
| final FieldODEState<T> s0 = getInitialState(); |
| final T[] y0 = s0.getState(); |
| final T[] y = MathArrays.buildArray(getField(), getDimension()); |
| T c = s0.getTime().subtract(t).exp(); |
| for (int i = 0; i < getDimension(); ++i) { |
| y[i] = c.multiply(y0[i]); |
| } |
| return y; |
| } |
| |
| } |