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Diffstat (limited to 'src/main/java/org/apache/commons/math3/ode/events/package-info.java')
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diff --git a/src/main/java/org/apache/commons/math3/ode/events/package-info.java b/src/main/java/org/apache/commons/math3/ode/events/package-info.java new file mode 100644 index 0000000..9d3b917 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/ode/events/package-info.java @@ -0,0 +1,96 @@ +/* + * 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. + */ +/** + * + * <p> + * This package provides classes to handle discrete events occurring during + * Ordinary Differential Equations integration. + * </p> + * + * <p> + * Discrete events detection is based on switching functions. The user provides + * a simple {@link org.apache.commons.math3.ode.events.EventHandler#g g(t, y)} + * function depending on the current time and state. The integrator will monitor + * the value of the function throughout integration range and will trigger the + * event when its sign changes. The magnitude of the value is almost irrelevant, + * it should however be continuous (but not necessarily smooth) for the sake of + * root finding. The steps are shortened as needed to ensure the events occur + * at step boundaries (even if the integrator is a fixed-step integrator). + * </p> + * + * <p> + * When an event is triggered, several different options are available: + * </p> + * <ul> + * <li>integration can be stopped (this is called a G-stop facility),</li> + * <li>the state vector or the derivatives can be changed,</li> + * <li>or integration can simply go on.</li> + * </ul> + * + * <p> + * The first case, G-stop, is the most common one. A typical use case is when an + * ODE must be solved up to some target state is reached, with a known value of + * the state but an unknown occurrence time. As an example, if we want to monitor + * a chemical reaction up to some predefined concentration for the first substance, + * we can use the following switching function setting: + * <pre> + * public double g(double t, double[] y) { + * return y[0] - targetConcentration; + * } + * + * public int eventOccurred(double t, double[] y) { + * return STOP; + * } + * </pre> + * </p> + * + * <p> + * The second case, change state vector or derivatives is encountered when dealing + * with discontinuous dynamical models. A typical case would be the motion of a + * spacecraft when thrusters are fired for orbital maneuvers. The acceleration is + * smooth as long as no maneuver are performed, depending only on gravity, drag, + * third body attraction, radiation pressure. Firing a thruster introduces a + * discontinuity that must be handled appropriately by the integrator. In such a case, + * we would use a switching function setting similar to this: + * <pre> + * public double g(double t, double[] y) { + * return (t - tManeuverStart) ∗ (t - tManeuverStop); + * } + * + * public int eventOccurred(double t, double[] y) { + * return RESET_DERIVATIVES; + * } + * </pre> + * </p> + * + * <p> + * The third case is useful mainly for monitoring purposes, a simple example is: + * <pre> + * public double g(double t, double[] y) { + * return y[0] - y[1]; + * } + * + * public int eventOccurred(double t, double[] y) { + * logger.log("y0(t) and y1(t) curves cross at t = " + t); + * return CONTINUE; + * } + * </pre> + * </p> + * + * + */ +package org.apache.commons.math3.ode.events; |