EpochDerivativesEquations.java
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package org.orekit.propagation.numerical;
import java.util.IdentityHashMap;
import java.util.Map;
import org.hipparchus.analysis.differentiation.Gradient;
import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
import org.hipparchus.linear.Array2DRowRealMatrix;
import org.hipparchus.linear.DecompositionSolver;
import org.hipparchus.linear.MatrixUtils;
import org.hipparchus.linear.QRDecomposition;
import org.hipparchus.linear.RealMatrix;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.forces.ForceModel;
import org.orekit.forces.gravity.ThirdBodyAttractionEpoch;
import org.orekit.propagation.FieldSpacecraftState;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.integration.AdditionalDerivativesProvider;
import org.orekit.propagation.integration.CombinedDerivatives;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterDriversList;
import org.orekit.utils.TimeSpanMap.Span;
/** Computes derivatives of the acceleration, including ThirdBodyAttraction.
*
* {@link AdditionalDerivativesProvider Provider} computing the partial derivatives
* of the state (orbit) with respect to initial state and force models parameters.
* <p>
* This set of equations are automatically added to a {@link NumericalPropagator numerical propagator}
* in order to compute partial derivatives of the orbit along with the orbit itself. This is
* useful for example in orbit determination applications.
* </p>
* <p>
* The partial derivatives with respect to initial state can be either dimension 6
* (orbit only) or 7 (orbit and mass).
* </p>
* <p>
* The partial derivatives with respect to force models parameters has a dimension
* equal to the number of selected parameters. Parameters selection is implemented at
* {@link ForceModel force models} level. Users must retrieve a {@link ParameterDriver
* parameter driver} using {@link ForceModel#getParameterDriver(String)} and then
* select it by calling {@link ParameterDriver#setSelected(boolean) setSelected(true)}.
* </p>
* <p>
* If several force models provide different {@link ParameterDriver drivers} for the
* same parameter name, selecting any of these drivers has the side effect of
* selecting all the drivers for this shared parameter. In this case, the partial
* derivatives will be the sum of the partial derivatives contributed by the
* corresponding force models. This case typically arises for central attraction
* coefficient, which has an influence on {@link org.orekit.forces.gravity.NewtonianAttraction
* Newtonian attraction}, {@link org.orekit.forces.gravity.HolmesFeatherstoneAttractionModel
* gravity field}, and {@link org.orekit.forces.gravity.Relativity relativity}.
* </p>
* @author Véronique Pommier-Maurussane
* @author Luc Maisonobe
* @since 10.2
*/
public class EpochDerivativesEquations
implements AdditionalDerivativesProvider {
/** State dimension, fixed to 6. */
public static final int STATE_DIMENSION = 6;
/** Propagator computing state evolution. */
private final NumericalPropagator propagator;
/** Selected parameters for Jacobian computation. */
private ParameterDriversList selected;
/** Parameters map. */
private Map<String, Integer> map;
/** Name. */
private final String name;
/** Simple constructor.
* <p>
* Upon construction, this set of equations is <em>automatically</em> added to
* the propagator by calling its {@link
* NumericalPropagator#addAdditionalDerivativesProvider(AdditionalDerivativesProvider)} method. So
* there is no need to call this method explicitly for these equations.
* </p>
* @param name name of the partial derivatives equations
* @param propagator the propagator that will handle the orbit propagation
*/
public EpochDerivativesEquations(final String name, final NumericalPropagator propagator) {
this.name = name;
this.selected = null;
this.map = null;
this.propagator = propagator;
propagator.addAdditionalDerivativesProvider(this);
}
/** {@inheritDoc} */
public String getName() {
return name;
}
/** {@inheritDoc} */
@Override
public int getDimension() {
freezeParametersSelection();
return 6 * (6 + selected.getNbParams() + 1);
}
/** Freeze the selected parameters from the force models.
*/
private void freezeParametersSelection() {
if (selected == null) {
// first pass: gather all parameters, binding similar names together
selected = new ParameterDriversList();
for (final ForceModel provider : propagator.getAllForceModels()) {
for (final ParameterDriver driver : provider.getParametersDrivers()) {
selected.add(driver);
}
}
// second pass: now that shared parameter names are bound together,
// their selections status have been synchronized, we can filter them
selected.filter(true);
// third pass: sort parameters lexicographically
selected.sort();
// fourth pass: set up a map between parameters drivers and matrices columns
map = new IdentityHashMap<>();
int parameterIndex = 0;
int previousParameterIndex = 0;
for (final ParameterDriver selectedDriver : selected.getDrivers()) {
for (final ForceModel provider : propagator.getAllForceModels()) {
for (final ParameterDriver driver : provider.getParametersDrivers()) {
if (driver.getName().equals(selectedDriver.getName())) {
previousParameterIndex = parameterIndex;
for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
map.put(span.getData(), previousParameterIndex++);
}
}
}
}
parameterIndex = previousParameterIndex;
}
}
}
/** Set the initial value of the Jacobian with respect to state and parameter.
* <p>
* This method is equivalent to call {@link #setInitialJacobians(SpacecraftState,
* double[][], double[][])} with dYdY0 set to the identity matrix and dYdP set
* to a zero matrix.
* </p>
* <p>
* The force models parameters for which partial derivatives are desired,
* <em>must</em> have been {@link ParameterDriver#setSelected(boolean) selected}
* before this method is called, so proper matrices dimensions are used.
* </p>
* @param s0 initial state
* @return state with initial Jacobians added
*/
public SpacecraftState setInitialJacobians(final SpacecraftState s0) {
freezeParametersSelection();
final int epochStateDimension = 6;
final double[][] dYdY0 = new double[epochStateDimension][epochStateDimension];
final double[][] dYdP = new double[epochStateDimension][selected.getNbValuesToEstimate() + 6];
for (int i = 0; i < epochStateDimension; ++i) {
dYdY0[i][i] = 1.0;
}
return setInitialJacobians(s0, dYdY0, dYdP);
}
/** Set the initial value of the Jacobian with respect to state and parameter.
* <p>
* The returned state must be added to the propagator (it is not done
* automatically, as the user may need to add more states to it).
* </p>
* <p>
* The force models parameters for which partial derivatives are desired,
* <em>must</em> have been {@link ParameterDriver#setSelected(boolean) selected}
* before this method is called, and the {@code dY1dP} matrix dimension <em>must</em>
* be consistent with the selection.
* </p>
* @param s1 current state
* @param dY1dY0 Jacobian of current state at time t₁ with respect
* to state at some previous time t₀ (must be 6x6)
* @param dY1dP Jacobian of current state at time t₁ with respect
* to parameters (may be null if no parameters are selected)
* @return state with initial Jacobians added
*/
public SpacecraftState setInitialJacobians(final SpacecraftState s1,
final double[][] dY1dY0, final double[][] dY1dP) {
freezeParametersSelection();
// Check dimensions
final int stateDimEpoch = dY1dY0.length;
if (stateDimEpoch != 6 || stateDimEpoch != dY1dY0[0].length) {
throw new OrekitException(OrekitMessages.STATE_JACOBIAN_NOT_6X6,
stateDimEpoch, dY1dY0[0].length);
}
if (dY1dP != null && stateDimEpoch != dY1dP.length) {
throw new OrekitException(OrekitMessages.STATE_AND_PARAMETERS_JACOBIANS_ROWS_MISMATCH,
stateDimEpoch, dY1dP.length);
}
// store the matrices as a single dimension array
final double[] p = new double[STATE_DIMENSION * (STATE_DIMENSION + selected.getNbValuesToEstimate()) + 6];
setInitialJacobians(s1, dY1dY0, dY1dP, p);
// set value in propagator
return s1.addAdditionalState(name, p);
}
/** Set the Jacobian with respect to state into a one-dimensional additional state array.
* <p>
* This method converts the Jacobians to Cartesian parameters and put the converted data
* in the one-dimensional {@code p} array.
* </p>
* @param state spacecraft state
* @param dY1dY0 Jacobian of current state at time t₁
* with respect to state at some previous time t₀
* @param dY1dP Jacobian of current state at time t₁
* with respect to parameters (may be null if there are no parameters)
* @param p placeholder where to put the one-dimensional additional state
*/
public void setInitialJacobians(final SpacecraftState state, final double[][] dY1dY0,
final double[][] dY1dP, final double[] p) {
// set up a converter
final RealMatrix dY1dC1 = MatrixUtils.createRealIdentityMatrix(STATE_DIMENSION);
final DecompositionSolver solver = new QRDecomposition(dY1dC1).getSolver();
// convert the provided state Jacobian
final RealMatrix dC1dY0 = solver.solve(new Array2DRowRealMatrix(dY1dY0, false));
// map the converted state Jacobian to one-dimensional array
int index = 0;
for (int i = 0; i < STATE_DIMENSION; ++i) {
for (int j = 0; j < STATE_DIMENSION; ++j) {
p[index++] = dC1dY0.getEntry(i, j);
}
}
if (selected.getNbValuesToEstimate() != 0) {
// convert the provided state Jacobian
final RealMatrix dC1dP = solver.solve(new Array2DRowRealMatrix(dY1dP, false));
// map the converted parameters Jacobian to one-dimensional array
for (int i = 0; i < STATE_DIMENSION; ++i) {
for (int j = 0; j < selected.getNbValuesToEstimate(); ++j) {
p[index++] = dC1dP.getEntry(i, j);
}
}
}
}
/** {@inheritDoc} */
public CombinedDerivatives combinedDerivatives(final SpacecraftState s) {
// initialize acceleration Jacobians to zero
final int paramDimEpoch = selected.getNbValuesToEstimate() + 1; // added epoch
final int dimEpoch = 3;
final double[][] dAccdParam = new double[dimEpoch][paramDimEpoch];
final double[][] dAccdPos = new double[dimEpoch][dimEpoch];
final double[][] dAccdVel = new double[dimEpoch][dimEpoch];
final NumericalGradientConverter fullConverter = new NumericalGradientConverter(s, 6, propagator.getAttitudeProvider());
final NumericalGradientConverter posOnlyConverter = new NumericalGradientConverter(s, 3, propagator.getAttitudeProvider());
// compute acceleration Jacobians, finishing with the largest force: Newtonian attraction
for (final ForceModel forceModel : propagator.getAllForceModels()) {
final NumericalGradientConverter converter = forceModel.dependsOnPositionOnly() ? posOnlyConverter : fullConverter;
final FieldSpacecraftState<Gradient> dsState = converter.getState(forceModel);
final Gradient[] parameters = converter.getParametersAtStateDate(dsState, forceModel);
final FieldVector3D<Gradient> acceleration = forceModel.acceleration(dsState, parameters);
final double[] derivativesX = acceleration.getX().getGradient();
final double[] derivativesY = acceleration.getY().getGradient();
final double[] derivativesZ = acceleration.getZ().getGradient();
// update Jacobians with respect to state
addToRow(derivativesX, 0, converter.getFreeStateParameters(), dAccdPos, dAccdVel);
addToRow(derivativesY, 1, converter.getFreeStateParameters(), dAccdPos, dAccdVel);
addToRow(derivativesZ, 2, converter.getFreeStateParameters(), dAccdPos, dAccdVel);
int index = converter.getFreeStateParameters();
for (ParameterDriver driver : forceModel.getParametersDrivers()) {
if (driver.isSelected()) {
for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {
final int parameterIndex = map.get(span.getData());
dAccdParam[0][parameterIndex] += derivativesX[index];
dAccdParam[1][parameterIndex] += derivativesY[index];
dAccdParam[2][parameterIndex] += derivativesZ[index];
++index;
}
}
}
// Add the derivatives of the acceleration w.r.t. the Epoch
if (forceModel instanceof ThirdBodyAttractionEpoch) {
final double[] parametersValues = new double[] {parameters[0].getValue()};
final double[] derivatives = ((ThirdBodyAttractionEpoch) forceModel).getDerivativesToEpoch(s, parametersValues);
dAccdParam[0][paramDimEpoch - 1] += derivatives[0];
dAccdParam[1][paramDimEpoch - 1] += derivatives[1];
dAccdParam[2][paramDimEpoch - 1] += derivatives[2];
}
}
// the variational equations of the complete state Jacobian matrix have the following form:
// [ | ] [ | ] [ | ]
// [ Adot | Bdot ] [ dVel/dPos = 0 | dVel/dVel = Id ] [ A | B ]
// [ | ] [ | ] [ | ]
// ---------+--------- ------------------+------------------- * ------+------
// [ | ] [ | ] [ | ]
// [ Cdot | Ddot ] = [ dAcc/dPos | dAcc/dVel ] [ C | D ]
// [ | ] [ | ] [ | ]
// The A, B, C and D sub-matrices and their derivatives (Adot ...) are 3x3 matrices
// The expanded multiplication above can be rewritten to take into account
// the fixed values found in the sub-matrices in the left factor. This leads to:
// [ Adot ] = [ C ]
// [ Bdot ] = [ D ]
// [ Cdot ] = [ dAcc/dPos ] * [ A ] + [ dAcc/dVel ] * [ C ]
// [ Ddot ] = [ dAcc/dPos ] * [ B ] + [ dAcc/dVel ] * [ D ]
// The following loops compute these expressions taking care of the mapping of the
// (A, B, C, D) matrices into the single dimension array p and of the mapping of the
// (Adot, Bdot, Cdot, Ddot) matrices into the single dimension array pDot.
// copy C and E into Adot and Bdot
final int stateDim = 6;
final double[] p = s.getAdditionalState(getName());
final double[] pDot = new double[p.length];
System.arraycopy(p, dimEpoch * stateDim, pDot, 0, dimEpoch * stateDim);
// compute Cdot and Ddot
for (int i = 0; i < dimEpoch; ++i) {
final double[] dAdPi = dAccdPos[i];
final double[] dAdVi = dAccdVel[i];
for (int j = 0; j < stateDim; ++j) {
pDot[(dimEpoch + i) * stateDim + j] =
dAdPi[0] * p[j] + dAdPi[1] * p[j + stateDim] + dAdPi[2] * p[j + 2 * stateDim] +
dAdVi[0] * p[j + 3 * stateDim] + dAdVi[1] * p[j + 4 * stateDim] + dAdVi[2] * p[j + 5 * stateDim];
}
}
for (int k = 0; k < paramDimEpoch; ++k) {
// the variational equations of the parameters Jacobian matrix are computed
// one column at a time, they have the following form:
// [ ] [ | ] [ ] [ ]
// [ Edot ] [ dVel/dPos = 0 | dVel/dVel = Id ] [ E ] [ dVel/dParam = 0 ]
// [ ] [ | ] [ ] [ ]
// -------- ------------------+------------------- * ----- + --------------------
// [ ] [ | ] [ ] [ ]
// [ Fdot ] = [ dAcc/dPos | dAcc/dVel ] [ F ] [ dAcc/dParam ]
// [ ] [ | ] [ ] [ ]
// The E and F sub-columns and their derivatives (Edot, Fdot) are 3 elements columns.
// The expanded multiplication and addition above can be rewritten to take into
// account the fixed values found in the sub-matrices in the left factor. This leads to:
// [ Edot ] = [ F ]
// [ Fdot ] = [ dAcc/dPos ] * [ E ] + [ dAcc/dVel ] * [ F ] + [ dAcc/dParam ]
// The following loops compute these expressions taking care of the mapping of the
// (E, F) columns into the single dimension array p and of the mapping of the
// (Edot, Fdot) columns into the single dimension array pDot.
// copy F into Edot
final int columnTop = stateDim * stateDim + k;
pDot[columnTop] = p[columnTop + 3 * paramDimEpoch];
pDot[columnTop + paramDimEpoch] = p[columnTop + 4 * paramDimEpoch];
pDot[columnTop + 2 * paramDimEpoch] = p[columnTop + 5 * paramDimEpoch];
// compute Fdot
for (int i = 0; i < dimEpoch; ++i) {
final double[] dAdP = dAccdPos[i];
final double[] dAdV = dAccdVel[i];
pDot[columnTop + (dimEpoch + i) * paramDimEpoch] =
dAccdParam[i][k] +
dAdP[0] * p[columnTop] + dAdP[1] * p[columnTop + paramDimEpoch] + dAdP[2] * p[columnTop + 2 * paramDimEpoch] +
dAdV[0] * p[columnTop + 3 * paramDimEpoch] + dAdV[1] * p[columnTop + 4 * paramDimEpoch] + dAdV[2] * p[columnTop + 5 * paramDimEpoch];
}
}
return new CombinedDerivatives(pDot, null);
}
/** Fill Jacobians rows.
* @param derivatives derivatives of a component of acceleration (along either x, y or z)
* @param index component index (0 for x, 1 for y, 2 for z)
* @param freeStateParameters number of free parameters, either 3 (position),
* 6 (position-velocity) or 7 (position-velocity-mass)
* @param dAccdPos Jacobian of acceleration with respect to spacecraft position
* @param dAccdVel Jacobian of acceleration with respect to spacecraft velocity
*/
private void addToRow(final double[] derivatives, final int index, final int freeStateParameters,
final double[][] dAccdPos, final double[][] dAccdVel) {
for (int i = 0; i < 3; ++i) {
dAccdPos[index][i] += derivatives[i];
}
if (freeStateParameters > 3) {
for (int i = 0; i < 3; ++i) {
dAccdVel[index][i] += derivatives[i + 3];
}
}
}
}