Package org.orekit.propagation.numerical

Class PartialDerivativesEquations

  • All Implemented Interfaces:
    AdditionalEquations
    public class PartialDerivativesEquations
extends Object
implements AdditionalEquations
    Set of additional equations computing the partial derivatives of the state (orbit) with respect to initial state and force models parameters.

    This set of equations are automatically added to a 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.

    The partial derivatives with respect to initial state can be either dimension 6 (orbit only) or 7 (orbit and mass).

    The partial derivatives with respect to force models parameters has a dimension equal to the number of selected parameters. Parameters selection is implemented at force models level. Users must retrieve a parameter driver using ForceModel.getParameterDriver(String) and then select it by calling setSelected(true).

    If several force models provide different 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 Newtonian attraction, gravity field, and relativity.

    Author:
    Véronique Pommier-Maurussane, Luc Maisonobe

    • Constructor Detail

      • PartialDerivativesEquations

        public PartialDerivativesEquations​(String name,
                                   NumericalPropagator propagator)
        Simple constructor.

        Upon construction, this set of equations is automatically added to the propagator by calling its AbstractIntegratedPropagator.addAdditionalEquations(AdditionalEquations) method. So there is no need to call this method explicitly for these equations.

        Parameters:
        name - name of the partial derivatives equations
        propagator - the propagator that will handle the orbit propagation

    • Method Detail

      • getName

        public String getName()
        Get the name of the additional state.
        Specified by:
        getName in interface AdditionalEquations
        Returns:
        name of the additional state

      • getSelectedParameters

        public ParameterDriversList getSelectedParameters()
        Get the selected parameters, in Jacobian matrix column order.

        The force models parameters for which partial derivatives are desired, must have been selected before this method is called, so the proper list is returned.

        Returns:
        selected parameters, in Jacobian matrix column order which is lexicographic order

      • setInitialJacobians

        public SpacecraftState setInitialJacobians​(SpacecraftState s0)
        Set the initial value of the Jacobian with respect to state and parameter.

        This method is equivalent to call setInitialJacobians(SpacecraftState, double[][], double[][]) with dYdY0 set to the identity matrix and dYdP set to a zero matrix.

        The force models parameters for which partial derivatives are desired, must have been selected before this method is called, so proper matrices dimensions are used.

        Parameters:
        s0 - initial state
        Returns:
        state with initial Jacobians added
        Since:
        9.0
        See Also:
        getSelectedParameters()

      • setInitialJacobians

        public SpacecraftState setInitialJacobians​(SpacecraftState s1,
                                           double[][] dY1dY0,
                                           double[][] dY1dP)
        Set the initial value of the Jacobian with respect to state and parameter.

        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).

        The force models parameters for which partial derivatives are desired, must have been selected before this method is called, and the dY1dP matrix dimension must be consistent with the selection.

        Parameters:
        s1 - current state
        dY1dY0 - Jacobian of current state at time t₁ with respect to state at some previous time t₀ (must be 6x6)
        dY1dP - Jacobian of current state at time t₁ with respect to parameters (may be null if no parameters are selected)
        Returns:
        state with initial Jacobians added
        See Also:
        getSelectedParameters()

      • computeDerivatives

        public double[] computeDerivatives​(SpacecraftState s,
                                   double[] pDot)
        Compute the derivatives related to the additional state parameters.

        When this method is called, the spacecraft state contains the main state (orbit, attitude and mass), all the states provided through the additional state providers registered to the propagator, and the additional state integrated using this equation. It does not contains any other states to be integrated alongside during the same propagation.

        Specified by:
        computeDerivatives in interface AdditionalEquations
        Parameters:
        s - current state information: date, kinematics, attitude, and additional state
        pDot - placeholder where the derivatives of the additional parameters should be put
        Returns:
        cumulative effect of the equations on the main state (may be null if equations do not change main state at all)