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+<html>
+<!--
+   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.
+  -->
+    <!-- $Revision: 613620 $ -->
+<body>
+<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.math.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>
+
+</body>
+</html>