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With inspiration from other libraries
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.ode;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.ode.sampling.FieldStepHandler;
import org.apache.commons.math3.ode.sampling.FieldStepInterpolator;
import org.apache.commons.math3.util.FastMath;
/**
* This class stores all information provided by an ODE integrator
* during the integration process and build a continuous model of the
* solution from this.
*
* This class act as a step handler from the integrator point of
* view. It is called iteratively during the integration process and
* stores a copy of all steps information in a sorted collection for
* later use. Once the integration process is over, the user can use
* the {@link #getInterpolatedState(RealFieldElement) getInterpolatedState}
* method to retrieve this information at any time. It is important to wait
* for the integration to be over before attempting to call {@link
* #getInterpolatedState(RealFieldElement)} because some internal
* variables are set only once the last step has been handled.
*
* This is useful for example if the main loop of the user
* application should remain independent from the integration process
* or if one needs to mimic the behaviour of an analytical model
* despite a numerical model is used (i.e. one needs the ability to
* get the model value at any time or to navigate through the
* data).
*
* If problem modeling is done with several separate
* integration phases for contiguous intervals, the same
* ContinuousOutputModel can be used as step handler for all
* integration phases as long as they are performed in order and in
* the same direction. As an example, one can extrapolate the
* trajectory of a satellite with one model (i.e. one set of
* differential equations) up to the beginning of a maneuver, use
* another more complex model including thrusters modeling and
* accurate attitude control during the maneuver, and revert to the
* first model after the end of the maneuver. If the same continuous
* output model handles the steps of all integration phases, the user
* do not need to bother when the maneuver begins or ends, he has all
* the data available in a transparent manner.
*
* One should be aware that the amount of data stored in a
* ContinuousOutputFieldModel instance can be important if the state vector
* is large, if the integration interval is long or if the steps are
* small (which can result from small tolerance settings in {@link
* org.apache.commons.math3.ode.nonstiff.AdaptiveStepsizeFieldIntegrator adaptive
* step size integrators}).
*
* @see FieldStepHandler
* @see FieldStepInterpolator
* @param the type of the field elements
* @since 3.6
*/
public class ContinuousOutputFieldModel>
implements FieldStepHandler {
/** Initial integration time. */
private T initialTime;
/** Final integration time. */
private T finalTime;
/** Integration direction indicator. */
private boolean forward;
/** Current interpolator index. */
private int index;
/** Steps table. */
private List> steps;
/** Simple constructor.
* Build an empty continuous output model.
*/
public ContinuousOutputFieldModel() {
steps = new ArrayList>();
initialTime = null;
finalTime = null;
forward = true;
index = 0;
}
/** Append another model at the end of the instance.
* @param model model to add at the end of the instance
* @exception MathIllegalArgumentException if the model to append is not
* compatible with the instance (dimension of the state vector,
* propagation direction, hole between the dates)
* @exception DimensionMismatchException if the dimensions of the states or
* the number of secondary states do not match
* @exception MaxCountExceededException if the number of functions evaluations is exceeded
* during step finalization
*/
public void append(final ContinuousOutputFieldModel model)
throws MathIllegalArgumentException, MaxCountExceededException {
if (model.steps.size() == 0) {
return;
}
if (steps.size() == 0) {
initialTime = model.initialTime;
forward = model.forward;
} else {
// safety checks
final FieldODEStateAndDerivative s1 = steps.get(0).getPreviousState();
final FieldODEStateAndDerivative s2 = model.steps.get(0).getPreviousState();
checkDimensionsEquality(s1.getStateDimension(), s2.getStateDimension());
checkDimensionsEquality(s1.getNumberOfSecondaryStates(), s2.getNumberOfSecondaryStates());
for (int i = 0; i < s1.getNumberOfSecondaryStates(); ++i) {
checkDimensionsEquality(s1.getSecondaryStateDimension(i), s2.getSecondaryStateDimension(i));
}
if (forward ^ model.forward) {
throw new MathIllegalArgumentException(LocalizedFormats.PROPAGATION_DIRECTION_MISMATCH);
}
final FieldStepInterpolator lastInterpolator = steps.get(index);
final T current = lastInterpolator.getCurrentState().getTime();
final T previous = lastInterpolator.getPreviousState().getTime();
final T step = current.subtract(previous);
final T gap = model.getInitialTime().subtract(current);
if (gap.abs().subtract(step.abs().multiply(1.0e-3)).getReal() > 0) {
throw new MathIllegalArgumentException(LocalizedFormats.HOLE_BETWEEN_MODELS_TIME_RANGES,
gap.abs().getReal());
}
}
for (FieldStepInterpolator interpolator : model.steps) {
steps.add(interpolator);
}
index = steps.size() - 1;
finalTime = (steps.get(index)).getCurrentState().getTime();
}
/** Check dimensions equality.
* @param d1 first dimension
* @param d2 second dimansion
* @exception DimensionMismatchException if dimensions do not match
*/
private void checkDimensionsEquality(final int d1, final int d2)
throws DimensionMismatchException {
if (d1 != d2) {
throw new DimensionMismatchException(d2, d1);
}
}
/** {@inheritDoc} */
public void init(final FieldODEStateAndDerivative initialState, final T t) {
initialTime = initialState.getTime();
finalTime = t;
forward = true;
index = 0;
steps.clear();
}
/** Handle the last accepted step.
* A copy of the information provided by the last step is stored in
* the instance for later use.
* @param interpolator interpolator for the last accepted step.
* @param isLast true if the step is the last one
* @exception MaxCountExceededException if the number of functions evaluations is exceeded
* during step finalization
*/
public void handleStep(final FieldStepInterpolator interpolator, final boolean isLast)
throws MaxCountExceededException {
if (steps.size() == 0) {
initialTime = interpolator.getPreviousState().getTime();
forward = interpolator.isForward();
}
steps.add(interpolator);
if (isLast) {
finalTime = interpolator.getCurrentState().getTime();
index = steps.size() - 1;
}
}
/**
* Get the initial integration time.
* @return initial integration time
*/
public T getInitialTime() {
return initialTime;
}
/**
* Get the final integration time.
* @return final integration time
*/
public T getFinalTime() {
return finalTime;
}
/**
* Get the state at interpolated time.
* @param time time of the interpolated point
* @return state at interpolated time
*/
public FieldODEStateAndDerivative getInterpolatedState(final T time) {
// initialize the search with the complete steps table
int iMin = 0;
final FieldStepInterpolator sMin = steps.get(iMin);
T tMin = sMin.getPreviousState().getTime().add(sMin.getCurrentState().getTime()).multiply(0.5);
int iMax = steps.size() - 1;
final FieldStepInterpolator sMax = steps.get(iMax);
T tMax = sMax.getPreviousState().getTime().add(sMax.getCurrentState().getTime()).multiply(0.5);
// handle points outside of the integration interval
// or in the first and last step
if (locatePoint(time, sMin) <= 0) {
index = iMin;
return sMin.getInterpolatedState(time);
}
if (locatePoint(time, sMax) >= 0) {
index = iMax;
return sMax.getInterpolatedState(time);
}
// reduction of the table slice size
while (iMax - iMin > 5) {
// use the last estimated index as the splitting index
final FieldStepInterpolator si = steps.get(index);
final int location = locatePoint(time, si);
if (location < 0) {
iMax = index;
tMax = si.getPreviousState().getTime().add(si.getCurrentState().getTime()).multiply(0.5);
} else if (location > 0) {
iMin = index;
tMin = si.getPreviousState().getTime().add(si.getCurrentState().getTime()).multiply(0.5);
} else {
// we have found the target step, no need to continue searching
return si.getInterpolatedState(time);
}
// compute a new estimate of the index in the reduced table slice
final int iMed = (iMin + iMax) / 2;
final FieldStepInterpolator sMed = steps.get(iMed);
final T tMed = sMed.getPreviousState().getTime().add(sMed.getCurrentState().getTime()).multiply(0.5);
if (tMed.subtract(tMin).abs().subtract(1.0e-6).getReal() < 0 ||
tMax.subtract(tMed).abs().subtract(1.0e-6).getReal() < 0) {
// too close to the bounds, we estimate using a simple dichotomy
index = iMed;
} else {
// estimate the index using a reverse quadratic polynomial
// (reverse means we have i = P(t), thus allowing to simply
// compute index = P(time) rather than solving a quadratic equation)
final T d12 = tMax.subtract(tMed);
final T d23 = tMed.subtract(tMin);
final T d13 = tMax.subtract(tMin);
final T dt1 = time.subtract(tMax);
final T dt2 = time.subtract(tMed);
final T dt3 = time.subtract(tMin);
final T iLagrange = dt2.multiply(dt3).multiply(d23).multiply(iMax).
subtract(dt1.multiply(dt3).multiply(d13).multiply(iMed)).
add( dt1.multiply(dt2).multiply(d12).multiply(iMin)).
divide(d12.multiply(d23).multiply(d13));
index = (int) FastMath.rint(iLagrange.getReal());
}
// force the next size reduction to be at least one tenth
final int low = FastMath.max(iMin + 1, (9 * iMin + iMax) / 10);
final int high = FastMath.min(iMax - 1, (iMin + 9 * iMax) / 10);
if (index < low) {
index = low;
} else if (index > high) {
index = high;
}
}
// now the table slice is very small, we perform an iterative search
index = iMin;
while (index <= iMax && locatePoint(time, steps.get(index)) > 0) {
++index;
}
return steps.get(index).getInterpolatedState(time);
}
/** Compare a step interval and a double.
* @param time point to locate
* @param interval step interval
* @return -1 if the double is before the interval, 0 if it is in
* the interval, and +1 if it is after the interval, according to
* the interval direction
*/
private int locatePoint(final T time, final FieldStepInterpolator interval) {
if (forward) {
if (time.subtract(interval.getPreviousState().getTime()).getReal() < 0) {
return -1;
} else if (time.subtract(interval.getCurrentState().getTime()).getReal() > 0) {
return +1;
} else {
return 0;
}
}
if (time.subtract(interval.getPreviousState().getTime()).getReal() > 0) {
return -1;
} else if (time.subtract(interval.getCurrentState().getTime()).getReal() < 0) {
return +1;
} else {
return 0;
}
}
}