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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.math.ode;
19  
20  /**
21   * This interface represents a handler that should be called after
22   * each successful step.
23   *
24   * <p>The ODE integrators compute the evolution of the state vector at
25   * some grid points that depend on their own internal algorithm. Once
26   * they have found a new grid point (possibly after having computed
27   * several evaluation of the derivative at intermediate points), they
28   * provide it to objects implementing this interface. These objects
29   * typically either ignore the intermediate steps and wait for the
30   * last one, store the points in an ephemeris, or forward them to
31   * specialized processing or output methods.</p>
32   *
33   * @see FirstOrderIntegrator
34   * @see SecondOrderIntegrator
35   * @see StepInterpolator
36   * @version $Revision: 620312 $ $Date: 2008-02-10 12:28:59 -0700 (Sun, 10 Feb 2008) $
37   * @since 1.2
38   */
39  
40  public interface StepHandler {
41  
42    /** Determines whether this handler needs dense output.
43     * <p>This method allows the integrator to avoid performing extra
44     * computation if the handler does not need dense output. If this
45     * method returns false, the integrator will call the {@link
46     * #handleStep} method with a {@link DummyStepInterpolator} rather
47     * than a custom interpolator.</p>
48     * @return true if the handler needs dense output
49     */
50    public boolean requiresDenseOutput();
51  
52    /** Reset the step handler.
53     * Initialize the internal data as required before the first step is
54     * handled.
55     */
56    public void reset();
57  
58    /**
59     * Handle the last accepted step
60     * @param interpolator interpolator for the last accepted step. For
61     * efficiency purposes, the various integrators reuse the same
62     * object on each call, so if the instance wants to keep it across
63     * all calls (for example to provide at the end of the integration a
64     * continuous model valid throughout the integration range, as the
65     * {@link ContinuousOutputModel ContinuousOutputModel} class does),
66     * it should build a local copy using the clone method of the
67     * interpolator and store this copy. Keeping only a reference to the
68     * interpolator and reusing it will result in unpredictable
69     * behaviour (potentially crashing the application).
70     * @param isLast true if the step is the last one
71     * @throws DerivativeException this exception is propagated to the
72     * caller if the underlying user function triggers one
73     */
74    public void handleStep(StepInterpolator interpolator, boolean isLast)
75      throws DerivativeException;
76      
77  }