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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.
+ */
+/**
+ *
+ * <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) &lowast; (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;