DSSTStateTransitionMatrixGenerator.java
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package org.orekit.propagation.semianalytical.dsst;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.exception.LocalizedCoreFormats;
import org.hipparchus.linear.MatrixUtils;
import org.hipparchus.linear.RealMatrix;
import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.integration.AdditionalDerivativesProvider;
import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
import org.orekit.propagation.semianalytical.dsst.utilities.FieldAuxiliaryElements;
import org.orekit.utils.DoubleArrayDictionary;
import org.orekit.utils.ParameterDriver;
/** Generator for State Transition Matrix.
* @author Luc Maisonobe
* @since 11.1
*/
class DSSTStateTransitionMatrixGenerator implements AdditionalDerivativesProvider {
/** Space dimension. */
private static final int SPACE_DIMENSION = 3;
/** Retrograde factor I.
* <p>
* DSST model needs equinoctial orbit as internal representation.
* Classical equinoctial elements have discontinuities when inclination
* is close to zero. In this representation, I = +1. <br>
* To avoid this discontinuity, another representation exists and equinoctial
* elements can be expressed in a different way, called "retrograde" orbit.
* This implies I = -1. <br>
* As Orekit doesn't implement the retrograde orbit, I is always set to +1.
* But for the sake of consistency with the theory, the retrograde factor
* has been kept in the formulas.
* </p>
*/
private static final int I = 1;
/** State dimension. */
public static final int STATE_DIMENSION = 2 * SPACE_DIMENSION;
/** Name of the Cartesian STM additional state. */
private final String stmName;
/** Force models used in propagation. */
private final List<DSSTForceModel> forceModels;
/** Attitude provider used in propagation. */
private final AttitudeProvider attitudeProvider;
/** Observers for partial derivatives. */
private final Map<String, DSSTPartialsObserver> partialsObservers;
/** Simple constructor.
* @param stmName name of the Cartesian STM additional state
* @param forceModels force models used in propagation
* @param attitudeProvider attitude provider used in propagation
*/
DSSTStateTransitionMatrixGenerator(final String stmName, final List<DSSTForceModel> forceModels,
final AttitudeProvider attitudeProvider) {
this.stmName = stmName;
this.forceModels = forceModels;
this.attitudeProvider = attitudeProvider;
this.partialsObservers = new HashMap<>();
}
/** Register an observer for partial derivatives.
* <p>
* The observer {@link DSSTPartialsObserver#partialsComputed(double[], double[]) partialsComputed}
* method will be called when partial derivatives are computed, as a side effect of
* calling {@link #generate(SpacecraftState)}
* </p>
* @param name name of the parameter driver this observer is interested in (may be null)
* @param observer observer to register
*/
void addObserver(final String name, final DSSTPartialsObserver observer) {
partialsObservers.put(name, observer);
}
/** {@inheritDoc} */
@Override
public String getName() {
return stmName;
}
/** {@inheritDoc} */
@Override
public int getDimension() {
return STATE_DIMENSION * STATE_DIMENSION;
}
/** {@inheritDoc} */
@Override
public boolean yield(final SpacecraftState state) {
return !state.hasAdditionalState(getName());
}
/** Set the initial value of the State Transition Matrix.
* <p>
* The returned state must be added to the propagator.
* </p>
* @param state initial state
* @param dYdY0 initial State Transition Matrix ∂Y/∂Y₀,
* if null (which is the most frequent case), assumed to be 6x6 identity
* @return state with initial STM (converted to Cartesian ∂C/∂Y₀) added
*/
SpacecraftState setInitialStateTransitionMatrix(final SpacecraftState state, final RealMatrix dYdY0) {
if (dYdY0 != null) {
if (dYdY0.getRowDimension() != STATE_DIMENSION ||
dYdY0.getColumnDimension() != STATE_DIMENSION) {
throw new OrekitException(LocalizedCoreFormats.DIMENSIONS_MISMATCH_2x2,
dYdY0.getRowDimension(), dYdY0.getColumnDimension(),
STATE_DIMENSION, STATE_DIMENSION);
}
}
// flatten matrix
final double[] flat = new double[STATE_DIMENSION * STATE_DIMENSION];
int k = 0;
for (int i = 0; i < STATE_DIMENSION; ++i) {
for (int j = 0; j < STATE_DIMENSION; ++j) {
flat[k++] = dYdY0.getEntry(i, j);
}
}
// set additional state
return state.addAdditionalState(stmName, flat);
}
/** {@inheritDoc} */
public double[] derivatives(final SpacecraftState state) {
final double[] p = state.getAdditionalState(getName());
final double[] res = new double[p.length];
// perform matrix multiplication with matrices flatten
final RealMatrix factor = computePartials(state);
int index = 0;
for (int i = 0; i < STATE_DIMENSION; ++i) {
for (int j = 0; j < STATE_DIMENSION; ++j) {
double sum = 0;
for (int k = 0; k < STATE_DIMENSION; ++k) {
sum += factor.getEntry(i, k) * p[j + k * STATE_DIMENSION];
}
res[index++] = sum;
}
}
return res;
}
/** Compute the various partial derivatives.
* @param state current spacecraft state
* @return factor matrix
*/
private RealMatrix computePartials(final SpacecraftState state) {
// set up containers for partial derivatives
final RealMatrix factor = MatrixUtils.createRealMatrix(STATE_DIMENSION, STATE_DIMENSION);
final DoubleArrayDictionary meanElementsPartials = new DoubleArrayDictionary();
final DSSTGradientConverter converter = new DSSTGradientConverter(state, attitudeProvider);
// Compute Jacobian
for (final DSSTForceModel forceModel : forceModels) {
final FieldSpacecraftState<Gradient> dsState = converter.getState(forceModel);
final Gradient[] parameters = converter.getParameters(dsState, forceModel);
final FieldAuxiliaryElements<Gradient> auxiliaryElements = new FieldAuxiliaryElements<>(dsState.getOrbit(), I);
final Gradient[] meanElementRate = forceModel.getMeanElementRate(dsState, auxiliaryElements, parameters);
final double[] derivativesA = meanElementRate[0].getGradient();
final double[] derivativesEx = meanElementRate[1].getGradient();
final double[] derivativesEy = meanElementRate[2].getGradient();
final double[] derivativesHx = meanElementRate[3].getGradient();
final double[] derivativesHy = meanElementRate[4].getGradient();
final double[] derivativesL = meanElementRate[5].getGradient();
// update Jacobian with respect to state
addToRow(derivativesA, 0, factor);
addToRow(derivativesEx, 1, factor);
addToRow(derivativesEy, 2, factor);
addToRow(derivativesHx, 3, factor);
addToRow(derivativesHy, 4, factor);
addToRow(derivativesL, 5, factor);
// partials derivatives with respect to parameters
int paramsIndex = converter.getFreeStateParameters();
for (ParameterDriver driver : forceModel.getParametersDrivers()) {
if (driver.isSelected()) {
// get the partials derivatives for this driver
DoubleArrayDictionary.Entry entry = meanElementsPartials.getEntry(driver.getName());
if (entry == null) {
// create an entry filled with zeroes
meanElementsPartials.put(driver.getName(), new double[STATE_DIMENSION]);
entry = meanElementsPartials.getEntry(driver.getName());
}
// add the contribution of the current force model
entry.increment(new double[] {
derivativesA[paramsIndex], derivativesEx[paramsIndex], derivativesEy[paramsIndex],
derivativesHx[paramsIndex], derivativesHy[paramsIndex], derivativesL[paramsIndex]
});
++paramsIndex;
}
}
}
// notify observers
for (Map.Entry<String, DSSTPartialsObserver> observersEntry : partialsObservers.entrySet()) {
final DoubleArrayDictionary.Entry entry = meanElementsPartials.getEntry(observersEntry.getKey());
observersEntry.getValue().partialsComputed(state, factor, entry == null ? new double[STATE_DIMENSION] : entry.getValue());
}
return factor;
}
/** Fill Jacobians rows.
* @param derivatives derivatives of a component
* @param index component index (0 for a, 1 for ex, 2 for ey, 3 for hx, 4 for hy, 5 for l)
* @param factor Jacobian of mean elements rate with respect to mean elements
*/
private void addToRow(final double[] derivatives, final int index, final RealMatrix factor) {
for (int i = 0; i < 6; i++) {
factor.addToEntry(index, i, derivatives[i]);
}
}
/** Interface for observing partials derivatives. */
public interface DSSTPartialsObserver {
/** Callback called when partial derivatives have been computed.
* @param state current spacecraft state
* @param factor factor matrix
* @param meanElementsPartials partials derivatives of mean elements rates with respect to the parameter driver
* that was registered (zero if no parameters were not selected or parameter is unknown)
*/
void partialsComputed(SpacecraftState state, RealMatrix factor, double[] meanElementsPartials);
}
}