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+/*
+ * 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.nonstiff;
+
+import org.apache.commons.math3.Field;
+import org.apache.commons.math3.RealFieldElement;
+import org.apache.commons.math3.ode.FieldEquationsMapper;
+import org.apache.commons.math3.ode.FieldODEStateAndDerivative;
+import org.apache.commons.math3.util.MathArrays;
+
+/**
+ * This class implements a simple Euler integrator for Ordinary
+ * Differential Equations.
+ *
+ * <p>The Euler algorithm is the simplest one that can be used to
+ * integrate ordinary differential equations. It is a simple inversion
+ * of the forward difference expression :
+ * <code>f'=(f(t+h)-f(t))/h</code> which leads to
+ * <code>f(t+h)=f(t)+hf'</code>. The interpolation scheme used for
+ * dense output is the linear scheme already used for integration.</p>
+ *
+ * <p>This algorithm looks cheap because it needs only one function
+ * evaluation per step. However, as it uses linear estimates, it needs
+ * very small steps to achieve high accuracy, and small steps lead to
+ * numerical errors and instabilities.</p>
+ *
+ * <p>This algorithm is almost never used and has been included in
+ * this package only as a comparison reference for more useful
+ * integrators.</p>
+ *
+ * @see MidpointFieldIntegrator
+ * @see ClassicalRungeKuttaFieldIntegrator
+ * @see GillFieldIntegrator
+ * @see ThreeEighthesFieldIntegrator
+ * @see LutherFieldIntegrator
+ * @param <T> the type of the field elements
+ * @since 3.6
+ */
+
+public class EulerFieldIntegrator<T extends RealFieldElement<T>> extends RungeKuttaFieldIntegrator<T> {
+
+ /** Simple constructor.
+ * Build an Euler integrator with the given step.
+ * @param field field to which the time and state vector elements belong
+ * @param step integration step
+ */
+ public EulerFieldIntegrator(final Field<T> field, final T step) {
+ super(field, "Euler", step);
+ }
+
+ /** {@inheritDoc} */
+ public T[] getC() {
+ return MathArrays.buildArray(getField(), 0);
+ }
+
+ /** {@inheritDoc} */
+ public T[][] getA() {
+ return MathArrays.buildArray(getField(), 0, 0);
+ }
+
+ /** {@inheritDoc} */
+ public T[] getB() {
+ final T[] b = MathArrays.buildArray(getField(), 1);
+ b[0] = getField().getOne();
+ return b;
+ }
+
+ /** {@inheritDoc} */
+ @Override
+ protected EulerFieldStepInterpolator<T>
+ createInterpolator(final boolean forward, T[][] yDotK,
+ final FieldODEStateAndDerivative<T> globalPreviousState,
+ final FieldODEStateAndDerivative<T> globalCurrentState,
+ final FieldEquationsMapper<T> mapper) {
+ return new EulerFieldStepInterpolator<T>(getField(), forward, yDotK,
+ globalPreviousState, globalCurrentState,
+ globalPreviousState, globalCurrentState,
+ mapper);
+ }
+
+}