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| <div class="subTitle">org.apache.commons.math3.ode.events</div> |
| <h2 title="Interface EventHandler" class="title">Interface EventHandler</h2> |
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| <dt>All Known Implementing Classes:</dt> |
| <dd><a href="../../../../../../org/apache/commons/math3/ode/events/EventFilter.html" title="class in org.apache.commons.math3.ode.events">EventFilter</a></dd> |
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| <br> |
| <pre>public interface <span class="strong">EventHandler</span></pre> |
| <div class="block">This interface represents a handler for discrete events triggered |
| during ODE integration. |
| |
| <p>Some events can be triggered at discrete times as an ODE problem |
| is solved. This occurs for example when the integration process |
| should be stopped as some state is reached (G-stop facility) when the |
| precise date is unknown a priori, or when the derivatives have |
| discontinuities, or simply when the user wants to monitor some |
| states boundaries crossings. |
| </p> |
| |
| <p>These events are defined as occurring when a <code>g</code> |
| switching function sign changes.</p> |
| |
| <p>Since events are only problem-dependent and are triggered by the |
| independent <i>time</i> variable and the state vector, they can |
| occur at virtually any time, unknown in advance. The integrators will |
| take care to avoid sign changes inside the steps, they will reduce |
| the step size when such an event is detected in order to put this |
| event exactly at the end of the current step. This guarantees that |
| step interpolation (which always has a one step scope) is relevant |
| even in presence of discontinuities. This is independent from the |
| stepsize control provided by integrators that monitor the local |
| error (this event handling feature is available for all integrators, |
| including fixed step ones).</p></div> |
| <dl><dt><span class="strong">Since:</span></dt> |
| <dd>1.2</dd> |
| <dt><span class="strong">Version:</span></dt> |
| <dd>$Id: EventHandler.java 1451658 2013-03-01 17:36:46Z luc $</dd></dl> |
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| <tr class="altColor"> |
| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html" title="enum in org.apache.commons.math3.ode.events">EventHandler.Action</a></strong></code> |
| <div class="block">Enumerate for actions to be performed when an event occurs.</div> |
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| <td class="colFirst"><code><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html" title="enum in org.apache.commons.math3.ode.events">EventHandler.Action</a></code></td> |
| <td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#eventOccurred(double, double[], boolean)">eventOccurred</a></strong>(double t, |
| double[] y, |
| boolean increasing)</code> |
| <div class="block">Handle an event and choose what to do next.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>double</code></td> |
| <td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#g(double, double[])">g</a></strong>(double t, |
| double[] y)</code> |
| <div class="block">Compute the value of the switching function.</div> |
| </td> |
| </tr> |
| <tr class="altColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#init(double, double[], double)">init</a></strong>(double t0, |
| double[] y0, |
| double t)</code> |
| <div class="block">Initialize event handler at the start of an ODE integration.</div> |
| </td> |
| </tr> |
| <tr class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><strong><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#resetState(double, double[])">resetState</a></strong>(double t, |
| double[] y)</code> |
| <div class="block">Reset the state prior to continue the integration.</div> |
| </td> |
| </tr> |
| </table> |
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| <h4>init</h4> |
| <pre>void init(double t0, |
| double[] y0, |
| double t)</pre> |
| <div class="block">Initialize event handler at the start of an ODE integration. |
| <p> |
| This method is called once at the start of the integration. It |
| may be used by the event handler to initialize some internal data |
| if needed. |
| </p></div> |
| <dl><dt><span class="strong">Parameters:</span></dt><dd><code>t0</code> - start value of the independent <i>time</i> variable</dd><dd><code>y0</code> - array containing the start value of the state vector</dd><dd><code>t</code> - target time for the integration</dd></dl> |
| </li> |
| </ul> |
| <a name="g(double, double[])"> |
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| <h4>g</h4> |
| <pre>double g(double t, |
| double[] y)</pre> |
| <div class="block">Compute the value of the switching function. |
| |
| <p>The discrete events are generated when the sign of this |
| switching function changes. The integrator will take care to change |
| the stepsize in such a way these events occur exactly at step boundaries. |
| The switching function must be continuous in its roots neighborhood |
| (but not necessarily smooth), as the integrator will need to find its |
| roots to locate precisely the events.</p> |
| <p>Also note that the integrator expect that once an event has occurred, |
| the sign of the switching function at the start of the next step (i.e. |
| just after the event) is the opposite of the sign just before the event. |
| This consistency between the steps <string>must</strong> be preserved, |
| otherwise <a href="../../../../../../org/apache/commons/math3/exception/NoBracketingException.html" title="class in org.apache.commons.math3.exception"><code>exceptions</code></a> related to root not being bracketed will occur.</p> |
| <p>This need for consistency is sometimes tricky to achieve. A typical |
| example is using an event to model a ball bouncing on the floor. The first |
| idea to represent this would be to have <code>g(t) = h(t)</code> where h is the |
| height above the floor at time <code>t</code>. When <code>g(t)</code> reaches 0, the |
| ball is on the floor, so it should bounce and the typical way to do this is |
| to reverse its vertical velocity. However, this would mean that before the |
| event <code>g(t)</code> was decreasing from positive values to 0, and after the |
| event <code>g(t)</code> would be increasing from 0 to positive values again. |
| Consistency is broken here! The solution here is to have <code>g(t) = sign |
| * h(t)</code>, where sign is a variable with initial value set to <code>+1</code>. Each |
| time <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#eventOccurred(double, double[], boolean)"><code>eventOccurred</code></a> is called, |
| <code>sign</code> is reset to <code>-sign</code>. This allows the <code>g(t)</code> |
| function to remain continuous (and even smooth) even across events, despite |
| <code>h(t)</code> is not. Basically, the event is used to <em>fold</em> <code>h(t)</code> |
| at bounce points, and <code>sign</code> is used to <em>unfold</em> it back, so the |
| solvers sees a <code>g(t)</code> function which behaves smoothly even across events.</p></div> |
| <dl><dt><span class="strong">Parameters:</span></dt><dd><code>t</code> - current value of the independent <i>time</i> variable</dd><dd><code>y</code> - array containing the current value of the state vector</dd> |
| <dt><span class="strong">Returns:</span></dt><dd>value of the g switching function</dd></dl> |
| </li> |
| </ul> |
| <a name="eventOccurred(double, double[], boolean)"> |
| <!-- --> |
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| <h4>eventOccurred</h4> |
| <pre><a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html" title="enum in org.apache.commons.math3.ode.events">EventHandler.Action</a> eventOccurred(double t, |
| double[] y, |
| boolean increasing)</pre> |
| <div class="block">Handle an event and choose what to do next. |
| |
| <p>This method is called when the integrator has accepted a step |
| ending exactly on a sign change of the function, just <em>before</em> |
| the step handler itself is called (see below for scheduling). It |
| allows the user to update his internal data to acknowledge the fact |
| the event has been handled (for example setting a flag in the <a href="../../../../../../org/apache/commons/math3/ode/FirstOrderDifferentialEquations.html" title="interface in org.apache.commons.math3.ode"><code>differential equations</code></a> to switch the derivatives computation in |
| case of discontinuity), or to direct the integrator to either stop |
| or continue integration, possibly with a reset state or derivatives.</p> |
| |
| <ul> |
| <li>if <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#STOP"><code>EventHandler.Action.STOP</code></a> is returned, the step handler will be called |
| with the <code>isLast</code> flag of the <a href="../../../../../../org/apache/commons/math3/ode/sampling/StepHandler.html#handleStep(org.apache.commons.math3.ode.sampling.StepInterpolator, boolean)"><code>handleStep</code></a> |
| method set to true and the integration will be stopped,</li> |
| <li>if <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_STATE"><code>EventHandler.Action.RESET_STATE</code></a> is returned, the <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#resetState(double, double[])"><code>resetState</code></a> method will be called once the step handler has |
| finished its task, and the integrator will also recompute the |
| derivatives,</li> |
| <li>if <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_DERIVATIVES"><code>EventHandler.Action.RESET_DERIVATIVES</code></a> is returned, the integrator |
| will recompute the derivatives, |
| <li>if <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#CONTINUE"><code>EventHandler.Action.CONTINUE</code></a> is returned, no specific action will |
| be taken (apart from having called this method) and integration |
| will continue.</li> |
| </ul> |
| |
| <p>The scheduling between this method and the <a href="../../../../../../org/apache/commons/math3/ode/sampling/StepHandler.html" title="interface in org.apache.commons.math3.ode.sampling"><code>StepHandler</code></a> method <a href="../../../../../../org/apache/commons/math3/ode/sampling/StepHandler.html#handleStep(org.apache.commons.math3.ode.sampling.StepInterpolator, boolean)"><code>handleStep(interpolator, isLast)</code></a> is to call this method first and |
| <code>handleStep</code> afterwards. This scheduling allows the integrator to |
| pass <code>true</code> as the <code>isLast</code> parameter to the step |
| handler to make it aware the step will be the last one if this method |
| returns <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#STOP"><code>EventHandler.Action.STOP</code></a>. As the interpolator may be used to navigate back |
| throughout the last step (as <a href="../../../../../../org/apache/commons/math3/ode/sampling/StepNormalizer.html" title="class in org.apache.commons.math3.ode.sampling"><code>StepNormalizer</code></a> |
| does for example), user code called by this method and user |
| code called by step handlers may experience apparently out of order values |
| of the independent time variable. As an example, if the same user object |
| implements both this <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html" title="interface in org.apache.commons.math3.ode.events"><code>EventHandler</code></a> interface and the |
| <a href="../../../../../../org/apache/commons/math3/ode/sampling/FixedStepHandler.html" title="interface in org.apache.commons.math3.ode.sampling"><code>FixedStepHandler</code></a> |
| interface, a <em>forward</em> integration may call its |
| <code>eventOccurred</code> method with t = 10 first and call its |
| <code>handleStep</code> method with t = 9 afterwards. Such out of order |
| calls are limited to the size of the integration step for <a href="../../../../../../org/apache/commons/math3/ode/sampling/StepHandler.html" title="interface in org.apache.commons.math3.ode.sampling"><code>variable step handlers</code></a> and |
| to the size of the fixed step for <a href="../../../../../../org/apache/commons/math3/ode/sampling/FixedStepHandler.html" title="interface in org.apache.commons.math3.ode.sampling"><code>fixed step handlers</code></a>.</p></div> |
| <dl><dt><span class="strong">Parameters:</span></dt><dd><code>t</code> - current value of the independent <i>time</i> variable</dd><dd><code>y</code> - array containing the current value of the state vector</dd><dd><code>increasing</code> - if true, the value of the switching function increases |
| when times increases around event (note that increase is measured with respect |
| to physical time, not with respect to integration which may go backward in time)</dd> |
| <dt><span class="strong">Returns:</span></dt><dd>indication of what the integrator should do next, this |
| value must be one of <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#STOP"><code>EventHandler.Action.STOP</code></a>, <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_STATE"><code>EventHandler.Action.RESET_STATE</code></a>, |
| <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_DERIVATIVES"><code>EventHandler.Action.RESET_DERIVATIVES</code></a> or <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#CONTINUE"><code>EventHandler.Action.CONTINUE</code></a></dd></dl> |
| </li> |
| </ul> |
| <a name="resetState(double, double[])"> |
| <!-- --> |
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| <h4>resetState</h4> |
| <pre>void resetState(double t, |
| double[] y)</pre> |
| <div class="block">Reset the state prior to continue the integration. |
| |
| <p>This method is called after the step handler has returned and |
| before the next step is started, but only when <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#eventOccurred(double, double[], boolean)"><code>eventOccurred(double, double[], boolean)</code></a> has itself returned the <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_STATE"><code>EventHandler.Action.RESET_STATE</code></a> |
| indicator. It allows the user to reset the state vector for the |
| next step, without perturbing the step handler of the finishing |
| step. If the <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.html#eventOccurred(double, double[], boolean)"><code>eventOccurred(double, double[], boolean)</code></a> never returns the <a href="../../../../../../org/apache/commons/math3/ode/events/EventHandler.Action.html#RESET_STATE"><code>EventHandler.Action.RESET_STATE</code></a> indicator, this function will never be called, and it is |
| safe to leave its body empty.</p></div> |
| <dl><dt><span class="strong">Parameters:</span></dt><dd><code>t</code> - current value of the independent <i>time</i> variable</dd><dd><code>y</code> - array containing the current value of the state vector |
| the new state should be put in the same array</dd></dl> |
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