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.sampling;
019
020 import java.io.Externalizable;
021
022 import org.apache.commons.math.ode.DerivativeException;
023 import org.apache.commons.math.ode.FirstOrderIntegrator;
024 import org.apache.commons.math.ode.SecondOrderIntegrator;
025
026 /** This interface represents an interpolator over the last step
027 * during an ODE integration.
028 *
029 * <p>The various ODE integrators provide objects implementing this
030 * interface to the step handlers. These objects are often custom
031 * objects tightly bound to the integrator internal algorithms. The
032 * handlers can use these objects to retrieve the state vector at
033 * intermediate times between the previous and the current grid points
034 * (this feature is often called dense output).</p>
035 * <p>One important thing to note is that the step handlers may be so
036 * tightly bound to the integrators that they often share some internal
037 * state arrays. This imply that one should <em>never</em> use a direct
038 * reference to a step interpolator outside of the step handler, either
039 * for future use or for use in another thread. If such a need arise, the
040 * step interpolator <em>must</em> be copied using the dedicated
041 * {@link #copy()} method.
042 * </p>
043 *
044 * @see FirstOrderIntegrator
045 * @see SecondOrderIntegrator
046 * @see StepHandler
047 * @version $Revision: 782431 $ $Date: 2009-06-07 15:04:37 -0400 (Sun, 07 Jun 2009) $
048 * @since 1.2
049 */
050
051 public interface StepInterpolator
052 extends Externalizable {
053
054 /**
055 * Get the previous grid point time.
056 * @return previous grid point time
057 */
058 public double getPreviousTime();
059
060 /**
061 * Get the current grid point time.
062 * @return current grid point time
063 */
064 public double getCurrentTime();
065
066 /**
067 * Get the time of the interpolated point.
068 * If {@link #setInterpolatedTime} has not been called, it returns
069 * the current grid point time.
070 * @return interpolation point time
071 */
072 public double getInterpolatedTime();
073
074 /**
075 * Set the time of the interpolated point.
076 * <p>Setting the time outside of the current step is now allowed, but
077 * should be used with care since the accuracy of the interpolator will
078 * probably be very poor far from this step. This allowance has been
079 * added to simplify implementation of search algorithms near the
080 * step endpoints.</p>
081 * <p>Setting the time changes the instance internal state. If a
082 * specific state must be preserved, a copy of the instance must be
083 * created using {@link #copy()}.</p>
084 * @param time time of the interpolated point
085 */
086 public void setInterpolatedTime(double time);
087
088 /**
089 * Get the state vector of the interpolated point.
090 * <p>The returned vector is a reference to a reused array, so
091 * it should not be modified and it should be copied if it needs
092 * to be preserved across several calls.</p>
093 * @return state vector at time {@link #getInterpolatedTime}
094 * @see #getInterpolatedDerivatives()
095 * @throws DerivativeException if this call induces an automatic
096 * step finalization that throws one
097 */
098 public double[] getInterpolatedState()
099 throws DerivativeException;
100
101 /**
102 * Get the derivatives of the state vector of the interpolated point.
103 * <p>The returned vector is a reference to a reused array, so
104 * it should not be modified and it should be copied if it needs
105 * to be preserved across several calls.</p>
106 * @return derivatives of the state vector at time {@link #getInterpolatedTime}
107 * @see #getInterpolatedState()
108 * @throws DerivativeException if this call induces an automatic
109 * step finalization that throws one
110 * @since 2.0
111 */
112 public double[] getInterpolatedDerivatives()
113 throws DerivativeException;
114
115 /** Check if the natural integration direction is forward.
116 * <p>This method provides the integration direction as specified by
117 * the integrator itself, it avoid some nasty problems in
118 * degenerated cases like null steps due to cancellation at step
119 * initialization, step control or discrete events
120 * triggering.</p>
121 * @return true if the integration variable (time) increases during
122 * integration
123 */
124 public boolean isForward();
125
126 /** Copy the instance.
127 * <p>The copied instance is guaranteed to be independent from the
128 * original one. Both can be used with different settings for
129 * interpolated time without any side effect.</p>
130 * @return a deep copy of the instance, which can be used independently.
131 * @throws DerivativeException if this call induces an automatic
132 * step finalization that throws one
133 * @see #setInterpolatedTime(double)
134 */
135 public StepInterpolator copy() throws DerivativeException;
136
137 }