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
018package org.apache.commons.math3.ode.sampling;
019
020import java.io.Externalizable;
021
022import org.apache.commons.math3.exception.MaxCountExceededException;
023
024/** This interface represents an interpolator over the last step
025 * during an ODE integration.
026 *
027 * <p>The various ODE integrators provide objects implementing this
028 * interface to the step handlers. These objects are often custom
029 * objects tightly bound to the integrator internal algorithms. The
030 * handlers can use these objects to retrieve the state vector at
031 * intermediate times between the previous and the current grid points
032 * (this feature is often called dense output).</p>
033 * <p>One important thing to note is that the step handlers may be so
034 * tightly bound to the integrators that they often share some internal
035 * state arrays. This imply that one should <em>never</em> use a direct
036 * reference to a step interpolator outside of the step handler, either
037 * for future use or for use in another thread. If such a need arise, the
038 * step interpolator <em>must</em> be copied using the dedicated
039 * {@link #copy()} method.
040 * </p>
041 *
042 * @see org.apache.commons.math3.ode.FirstOrderIntegrator
043 * @see org.apache.commons.math3.ode.SecondOrderIntegrator
044 * @see StepHandler
045 * @version $Id: StepInterpolator.java 1416643 2012-12-03 19:37:14Z tn $
046 * @since 1.2
047 */
048
049public interface StepInterpolator extends Externalizable {
050
051  /**
052   * Get the previous grid point time.
053   * @return previous grid point time
054   */
055  double getPreviousTime();
056
057  /**
058   * Get the current grid point time.
059   * @return current grid point time
060   */
061  double getCurrentTime();
062
063  /**
064   * Get the time of the interpolated point.
065   * If {@link #setInterpolatedTime} has not been called, it returns
066   * the current grid point time.
067   * @return interpolation point time
068   */
069  double getInterpolatedTime();
070
071  /**
072   * Set the time of the interpolated point.
073   * <p>Setting the time outside of the current step is now allowed, but
074   * should be used with care since the accuracy of the interpolator will
075   * probably be very poor far from this step. This allowance has been
076   * added to simplify implementation of search algorithms near the
077   * step endpoints.</p>
078   * <p>Setting the time changes the instance internal state. If a
079   * specific state must be preserved, a copy of the instance must be
080   * created using {@link #copy()}.</p>
081   * @param time time of the interpolated point
082   */
083  void setInterpolatedTime(double time);
084
085  /**
086   * Get the state vector of the interpolated point.
087   * <p>The returned vector is a reference to a reused array, so
088   * it should not be modified and it should be copied if it needs
089   * to be preserved across several calls.</p>
090   * @return state vector at time {@link #getInterpolatedTime}
091   * @see #getInterpolatedDerivatives()
092   * @exception MaxCountExceededException if the number of functions evaluations is exceeded
093   */
094  double[] getInterpolatedState() throws MaxCountExceededException;
095
096  /**
097   * Get the derivatives of the state vector of the interpolated point.
098   * <p>The returned vector is a reference to a reused array, so
099   * it should not be modified and it should be copied if it needs
100   * to be preserved across several calls.</p>
101   * @return derivatives of the state vector at time {@link #getInterpolatedTime}
102   * @see #getInterpolatedState()
103   * @since 2.0
104   * @exception MaxCountExceededException if the number of functions evaluations is exceeded
105   */
106  double[] getInterpolatedDerivatives() throws MaxCountExceededException;
107
108  /** Get the interpolated secondary state corresponding to the secondary equations.
109   * <p>The returned vector is a reference to a reused array, so
110   * it should not be modified and it should be copied if it needs
111   * to be preserved across several calls.</p>
112   * @param index index of the secondary set, as returned by {@link
113   * org.apache.commons.math3.ode.ExpandableStatefulODE#addSecondaryEquations(
114   * org.apache.commons.math3.ode.SecondaryEquations)
115   * ExpandableStatefulODE.addSecondaryEquations(SecondaryEquations)}
116   * @return interpolated secondary state at the current interpolation date
117   * @see #getInterpolatedState()
118   * @see #getInterpolatedDerivatives()
119   * @see #getInterpolatedSecondaryDerivatives(int)
120   * @see #setInterpolatedTime(double)
121   * @since 3.0
122   * @exception MaxCountExceededException if the number of functions evaluations is exceeded
123   */
124  double[] getInterpolatedSecondaryState(int index) throws MaxCountExceededException;
125
126  /** Get the interpolated secondary derivatives corresponding to the secondary equations.
127   * <p>The returned vector is a reference to a reused array, so
128   * it should not be modified and it should be copied if it needs
129   * to be preserved across several calls.</p>
130   * @param index index of the secondary set, as returned by {@link
131   * org.apache.commons.math3.ode.ExpandableStatefulODE#addSecondaryEquations(
132   * org.apache.commons.math3.ode.SecondaryEquations)
133   * ExpandableStatefulODE.addSecondaryEquations(SecondaryEquations)}
134   * @return interpolated secondary derivatives at the current interpolation date
135   * @see #getInterpolatedState()
136   * @see #getInterpolatedDerivatives()
137   * @see #getInterpolatedSecondaryState(int)
138   * @see #setInterpolatedTime(double)
139   * @since 3.0
140   * @exception MaxCountExceededException if the number of functions evaluations is exceeded
141   */
142  double[] getInterpolatedSecondaryDerivatives(int index) throws MaxCountExceededException;
143
144  /** Check if the natural integration direction is forward.
145   * <p>This method provides the integration direction as specified by
146   * the integrator itself, it avoid some nasty problems in
147   * degenerated cases like null steps due to cancellation at step
148   * initialization, step control or discrete events
149   * triggering.</p>
150   * @return true if the integration variable (time) increases during
151   * integration
152   */
153  boolean isForward();
154
155  /** Copy the instance.
156   * <p>The copied instance is guaranteed to be independent from the
157   * original one. Both can be used with different settings for
158   * interpolated time without any side effect.</p>
159   * @return a deep copy of the instance, which can be used independently.
160   * @see #setInterpolatedTime(double)
161   * @exception MaxCountExceededException if the number of functions evaluations is exceeded
162   * during step finalization
163   */
164   StepInterpolator copy() throws MaxCountExceededException;
165
166}