DSSTStateTransitionMatrixGenerator.java

  1. /* Copyright 2002-2022 CS GROUP
  2.  * Licensed to CS GROUP (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS 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. package org.orekit.propagation.semianalytical.dsst;

  19. import java.util.HashMap;
  20. import java.util.List;
  21. import java.util.Map;

  23. import org.hipparchus.analysis.differentiation.Gradient;
  24. import org.hipparchus.exception.LocalizedCoreFormats;
  25. import org.hipparchus.linear.MatrixUtils;
  26. import org.hipparchus.linear.RealMatrix;
  27. import org.orekit.attitudes.AttitudeProvider;
  28. import org.orekit.errors.OrekitException;
  29. import org.orekit.propagation.FieldSpacecraftState;
  30. import org.orekit.propagation.SpacecraftState;
  31. import org.orekit.propagation.integration.AdditionalDerivativesProvider;
  32. import org.orekit.propagation.semianalytical.dsst.forces.DSSTForceModel;
  33. import org.orekit.propagation.semianalytical.dsst.utilities.FieldAuxiliaryElements;
  34. import org.orekit.utils.DoubleArrayDictionary;
  35. import org.orekit.utils.ParameterDriver;

  37. /** Generator for State Transition Matrix.
  38.  * @author Luc Maisonobe
  39.  * @since 11.1
  40.  */
  41. class DSSTStateTransitionMatrixGenerator implements AdditionalDerivativesProvider {

  43.     /** Space dimension. */
  44.     private static final int SPACE_DIMENSION = 3;

  46.     /** Retrograde factor I.
  47.      *  <p>
  48.      *  DSST model needs equinoctial orbit as internal representation.
  49.      *  Classical equinoctial elements have discontinuities when inclination
  50.      *  is close to zero. In this representation, I = +1. <br>
  51.      *  To avoid this discontinuity, another representation exists and equinoctial
  52.      *  elements can be expressed in a different way, called "retrograde" orbit.
  53.      *  This implies I = -1. <br>
  54.      *  As Orekit doesn't implement the retrograde orbit, I is always set to +1.
  55.      *  But for the sake of consistency with the theory, the retrograde factor
  56.      *  has been kept in the formulas.
  57.      *  </p>
  58.      */
  59.     private static final int I = 1;

  61.     /** State dimension. */
  62.     public static final int STATE_DIMENSION = 2 * SPACE_DIMENSION;

  64.     /** Name of the Cartesian STM additional state. */
  65.     private final String stmName;

  67.     /** Force models used in propagation. */
  68.     private final List<DSSTForceModel> forceModels;

  70.     /** Attitude provider used in propagation. */
  71.     private final AttitudeProvider attitudeProvider;

  73.     /** Observers for partial derivatives. */
  74.     private final Map<String, DSSTPartialsObserver> partialsObservers;

  76.     /** Simple constructor.
  77.      * @param stmName name of the Cartesian STM additional state
  78.      * @param forceModels force models used in propagation
  79.      * @param attitudeProvider attitude provider used in propagation
  80.      */
  81.     DSSTStateTransitionMatrixGenerator(final String stmName, final List<DSSTForceModel> forceModels,
  82.                                        final AttitudeProvider attitudeProvider) {
  83.         this.stmName           = stmName;
  84.         this.forceModels       = forceModels;
  85.         this.attitudeProvider  = attitudeProvider;
  86.         this.partialsObservers = new HashMap<>();
  87.     }

  89.     /** Register an observer for partial derivatives.
  90.      * <p>
  91.      * The observer {@link DSSTPartialsObserver#partialsComputed(double[], double[]) partialsComputed}
  92.      * method will be called when partial derivatives are computed, as a side effect of
  93.      * calling {@link #generate(SpacecraftState)}
  94.      * </p>
  95.      * @param name name of the parameter driver this observer is interested in (may be null)
  96.      * @param observer observer to register
  97.      */
  98.     void addObserver(final String name, final DSSTPartialsObserver observer) {
  99.         partialsObservers.put(name, observer);
  100.     }

  102.     /** {@inheritDoc} */
  103.     @Override
  104.     public String getName() {
  105.         return stmName;
  106.     }

  108.     /** {@inheritDoc} */
  109.     @Override
  110.     public int getDimension() {
  111.         return STATE_DIMENSION * STATE_DIMENSION;
  112.     }

  114.     /** {@inheritDoc} */
  115.     @Override
  116.     public boolean yield(final SpacecraftState state) {
  117.         return !state.hasAdditionalState(getName());
  118.     }

  120.     /** Set the initial value of the State Transition Matrix.
  121.      * <p>
  122.      * The returned state must be added to the propagator.
  123.      * </p>
  124.      * @param state initial state
  125.      * @param dYdY0 initial State Transition Matrix ∂Y/∂Y₀,
  126.      * if null (which is the most frequent case), assumed to be 6x6 identity
  127.      * @return state with initial STM (converted to Cartesian ∂C/∂Y₀) added
  128.      */
  129.     SpacecraftState setInitialStateTransitionMatrix(final SpacecraftState state, final RealMatrix dYdY0) {

  131.         if (dYdY0 != null) {
  132.             if (dYdY0.getRowDimension() != STATE_DIMENSION ||
  133.                             dYdY0.getColumnDimension() != STATE_DIMENSION) {
  134.                 throw new OrekitException(LocalizedCoreFormats.DIMENSIONS_MISMATCH_2x2,
  135.                                           dYdY0.getRowDimension(), dYdY0.getColumnDimension(),
  136.                                           STATE_DIMENSION, STATE_DIMENSION);
  137.             }
  138.         }

  140.         // flatten matrix
  141.         final double[] flat = new double[STATE_DIMENSION * STATE_DIMENSION];
  142.         int k = 0;
  143.         for (int i = 0; i < STATE_DIMENSION; ++i) {
  144.             for (int j = 0; j < STATE_DIMENSION; ++j) {
  145.                 flat[k++] = dYdY0.getEntry(i, j);
  146.             }
  147.         }

  149.         // set additional state
  150.         return state.addAdditionalState(stmName, flat);

  152.     }

  154.     /** {@inheritDoc} */
  155.     public double[] derivatives(final SpacecraftState state) {

  157.         final double[] p = state.getAdditionalState(getName());
  158.         final double[] res = new double[p.length];

  160.         // perform matrix multiplication with matrices flatten
  161.         final RealMatrix factor = computePartials(state);
  162.         int index = 0;
  163.         for (int i = 0; i < STATE_DIMENSION; ++i) {
  164.             for (int j = 0; j < STATE_DIMENSION; ++j) {
  165.                 double sum = 0;
  166.                 for (int k = 0; k < STATE_DIMENSION; ++k) {
  167.                     sum += factor.getEntry(i, k) * p[j + k * STATE_DIMENSION];
  168.                 }
  169.                 res[index++] = sum;
  170.             }
  171.         }

  173.         return res;

  175.     }

  177.     /** Compute the various partial derivatives.
  178.      * @param state current spacecraft state
  179.      * @return factor matrix
  180.      */
  181.     private RealMatrix computePartials(final SpacecraftState state) {

  183.         // set up containers for partial derivatives
  184.         final RealMatrix            factor               = MatrixUtils.createRealMatrix(STATE_DIMENSION, STATE_DIMENSION);
  185.         final DoubleArrayDictionary meanElementsPartials = new DoubleArrayDictionary();
  186.         final DSSTGradientConverter converter            = new DSSTGradientConverter(state, attitudeProvider);

  188.         // Compute Jacobian
  189.         for (final DSSTForceModel forceModel : forceModels) {

  191.             final FieldSpacecraftState<Gradient> dsState = converter.getState(forceModel);
  192.             final Gradient[] parameters = converter.getParameters(dsState, forceModel);
  193.             final FieldAuxiliaryElements<Gradient> auxiliaryElements = new FieldAuxiliaryElements<>(dsState.getOrbit(), I);

  195.             final Gradient[] meanElementRate = forceModel.getMeanElementRate(dsState, auxiliaryElements, parameters);
  196.             final double[] derivativesA  = meanElementRate[0].getGradient();
  197.             final double[] derivativesEx = meanElementRate[1].getGradient();
  198.             final double[] derivativesEy = meanElementRate[2].getGradient();
  199.             final double[] derivativesHx = meanElementRate[3].getGradient();
  200.             final double[] derivativesHy = meanElementRate[4].getGradient();
  201.             final double[] derivativesL  = meanElementRate[5].getGradient();

  203.             // update Jacobian with respect to state
  204.             addToRow(derivativesA,  0, factor);
  205.             addToRow(derivativesEx, 1, factor);
  206.             addToRow(derivativesEy, 2, factor);
  207.             addToRow(derivativesHx, 3, factor);
  208.             addToRow(derivativesHy, 4, factor);
  209.             addToRow(derivativesL,  5, factor);

  211.             // partials derivatives with respect to parameters
  212.             int paramsIndex = converter.getFreeStateParameters();
  213.             for (ParameterDriver driver : forceModel.getParametersDrivers()) {
  214.                 if (driver.isSelected()) {

  216.                     // get the partials derivatives for this driver
  217.                     DoubleArrayDictionary.Entry entry = meanElementsPartials.getEntry(driver.getName());
  218.                     if (entry == null) {
  219.                         // create an entry filled with zeroes
  220.                         meanElementsPartials.put(driver.getName(), new double[STATE_DIMENSION]);
  221.                         entry = meanElementsPartials.getEntry(driver.getName());
  222.                     }

  224.                     // add the contribution of the current force model
  225.                     entry.increment(new double[] {
  226.                         derivativesA[paramsIndex], derivativesEx[paramsIndex], derivativesEy[paramsIndex],
  227.                         derivativesHx[paramsIndex], derivativesHy[paramsIndex], derivativesL[paramsIndex]
  228.                     });
  229.                     ++paramsIndex;

  231.                 }
  232.             }

  234.         }

  236.         // notify observers
  237.         for (Map.Entry<String, DSSTPartialsObserver> observersEntry : partialsObservers.entrySet()) {
  238.             final DoubleArrayDictionary.Entry entry = meanElementsPartials.getEntry(observersEntry.getKey());
  239.             observersEntry.getValue().partialsComputed(state, factor, entry == null ? new double[STATE_DIMENSION] : entry.getValue());
  240.         }

  242.         return factor;

  244.     }

  246.     /** Fill Jacobians rows.
  247.      * @param derivatives derivatives of a component
  248.      * @param index component index (0 for a, 1 for ex, 2 for ey, 3 for hx, 4 for hy, 5 for l)
  249.      * @param factor Jacobian of mean elements rate with respect to mean elements
  250.      */
  251.     private void addToRow(final double[] derivatives, final int index, final RealMatrix factor) {
  252.         for (int i = 0; i < 6; i++) {
  253.             factor.addToEntry(index, i, derivatives[i]);
  254.         }
  255.     }

  257.     /** Interface for observing partials derivatives. */
  258.     public interface DSSTPartialsObserver {

  260.         /** Callback called when partial derivatives have been computed.
  261.          * @param state current spacecraft state
  262.          * @param factor factor matrix
  263.          * @param meanElementsPartials partials derivatives of mean elements rates with respect to the parameter driver
  264.          * that was registered (zero if no parameters were not selected or parameter is unknown)
  265.          */
  266.         void partialsComputed(SpacecraftState state, RealMatrix factor, double[] meanElementsPartials);

  268.     }

  270. }
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