001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018 package org.apache.commons.math.ode.jacobians;
019
020 import org.apache.commons.math.ode.DerivativeException;
021
022 /**
023 * This interface represents a handler that should be called after
024 * each successful step.
025 *
026 * <p>The ODE integrators compute the evolution of the state vector at
027 * some grid points that depend on their own internal algorithm. Once
028 * they have found a new grid point (possibly after having computed
029 * several evaluation of the derivative at intermediate points), they
030 * provide it to objects implementing this interface. These objects
031 * typically either ignore the intermediate steps and wait for the
032 * last one, store the points in an ephemeris, or forward them to
033 * specialized processing or output methods.</p>
034 *
035 * <p>Note that is is possible to register a {@link
036 * org.apache.commons.math.ode.sampling.StepHandler classical step handler}
037 * in the low level integrator used to build a {@link FirstOrderIntegratorWithJacobians}
038 * rather than implementing this class. The step handlers registered at low level
039 * will see the big compound state whether the step handlers defined by this interface
040 * see the original state, and its jacobians in separate arrays.</p>
041 *
042 * <p>The compound state is guaranteed to contain the original state in the first
043 * elements, followed by the jacobian with respect to initial state (in row order),
044 * followed by the jacobian with respect to parameters (in row order). If for example
045 * the original state dimension is 6 and there are 3 parameters, the compound state will
046 * be a 60 elements array. The first 6 elements will be the original state, the next 36
047 * elements will be the jacobian with respect to initial state, and the remaining 18 elements
048 * will be the jacobian with respect to parameters.</p>
049 *
050 * <p>Dealing with low level step handlers is cumbersome if one really needs the jacobians
051 * in these methods, but it also prevents many data being copied back and forth between
052 * state and jacobians on one side and compound state on the other side. So for performance
053 * reasons, it is recommended to use this interface <em>only</em> if jacobians are really
054 * needed and to use lower level handlers if only state is needed.</p>
055 *
056 * @see FirstOrderIntegratorWithJacobians
057 * @see StepInterpolatorWithJacobians
058 * @version $Revision: 920131 $ $Date: 2010-03-07 17:19:18 -0500 (Sun, 07 Mar 2010) $
059 * @since 2.1
060 */
061
062 public interface StepHandlerWithJacobians {
063
064 /** Determines whether this handler needs dense output.
065 * <p>This method allows the integrator to avoid performing extra
066 * computation if the handler does not need dense output.</p>
067 * @return true if the handler needs dense output
068 */
069 boolean requiresDenseOutput();
070
071 /** Reset the step handler.
072 * Initialize the internal data as required before the first step is
073 * handled.
074 */
075 void reset();
076
077 /**
078 * Handle the last accepted step
079 * @param interpolator interpolator for the last accepted step. For
080 * efficiency purposes, the various integrators reuse the same
081 * object on each call, so if the instance wants to keep it across
082 * all calls (for example to provide at the end of the integration a
083 * continuous model valid throughout the integration range, as the
084 * {@link org.apache.commons.math.ode.ContinuousOutputModel
085 * ContinuousOutputModel} class does), it should build a local copy
086 * using the clone method of the interpolator and store this copy.
087 * Keeping only a reference to the interpolator and reusing it will
088 * result in unpredictable behavior (potentially crashing the application).
089 * @param isLast true if the step is the last one
090 * @throws DerivativeException this exception is propagated to the
091 * caller if the underlying user function triggers one
092 */
093 void handleStep(StepInterpolatorWithJacobians interpolator, boolean isLast) throws DerivativeException;
094
095 }