| /* |
| * 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> |
| * y1'' = -y1/r^3 y1 (0) = 1-e y1' (0) = 0 |
| * y2'' = -y2/r^3 y2 (0) = 0 y2' (0) =sqrt((1+e)/(1-e)) |
| * r = sqrt (y1^2 + y2^2), e = 0.9 |
| * </pre> |
| * This is a two-body problem in the plane which can be solved by |
| * Kepler's equation |
| * <pre> |
| * y1 (t) = ... |
| * </pre> |
| * </p> |
| |
| * @param <T> the type of the field elements |
| */ |
| public class TestFieldProblem3<T extends RealFieldElement<T>> |
| extends TestFieldProblemAbstract<T> { |
| |
| /** Eccentricity */ |
| T e; |
| |
| /** |
| * Simple constructor. |
| * @param field field to which elements belong |
| * @param e eccentricity |
| */ |
| public TestFieldProblem3(Field<T> field, T e) { |
| super(field); |
| this.e = e; |
| T[] y0 = MathArrays.buildArray(field, 4); |
| y0[0] = e.subtract(1).negate(); |
| y0[1] = field.getZero(); |
| y0[2] = field.getZero(); |
| y0[3] = e.add(1).divide(y0[0]).sqrt(); |
| setInitialConditions(convert(0.0), y0); |
| setFinalConditions(convert(20.0)); |
| setErrorScale(convert(1.0, 1.0, 1.0, 1.0)); |
| } |
| |
| /** |
| * Simple constructor. |
| * @param field field to which elements belong |
| */ |
| public TestFieldProblem3(Field<T> field) { |
| this(field, field.getZero().add(0.1)); |
| } |
| |
| @Override |
| public T[] doComputeDerivatives(T t, T[] y) { |
| |
| final T[] yDot = MathArrays.buildArray(getField(), getDimension()); |
| |
| // current radius |
| T r2 = y[0].multiply(y[0]).add(y[1].multiply(y[1])); |
| T invR3 = r2.multiply(r2.sqrt()).reciprocal(); |
| |
| // compute the derivatives |
| yDot[0] = y[2]; |
| yDot[1] = y[3]; |
| yDot[2] = invR3.negate().multiply(y[0]); |
| yDot[3] = invR3.negate().multiply(y[1]); |
| |
| return yDot; |
| |
| } |
| |
| @Override |
| public T[] computeTheoreticalState(T t) { |
| |
| final T[] y = MathArrays.buildArray(getField(), getDimension()); |
| |
| // solve Kepler's equation |
| T E = t; |
| T d = convert(0); |
| T corr = convert(999.0); |
| for (int i = 0; (i < 50) && (corr.abs().getReal() > 1.0e-12); ++i) { |
| T f2 = e.multiply(E.sin()); |
| T f0 = d.subtract(f2); |
| T f1 = e.multiply(E.cos()).subtract(1).negate(); |
| T f12 = f1.add(f1); |
| corr = f0.multiply(f12).divide(f1.multiply(f12).subtract(f0.multiply(f2))); |
| d = d.subtract(corr); |
| E = t.add(d); |
| } |
| |
| T cosE = E.cos(); |
| T sinE = E.sin(); |
| |
| y[0] = cosE.subtract(e); |
| y[1] = e.multiply(e).subtract(1).negate().sqrt().multiply(sinE); |
| y[2] = sinE.divide(e.multiply(cosE).subtract(1)); |
| y[3] = e.multiply(e).subtract(1).negate().sqrt().multiply(cosE).divide(e.multiply(cosE).subtract(1).negate()); |
| |
| return y; |
| |
| } |
| |
| } |