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17  package org.orekit.propagation.integration;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.orekit.propagation.FieldSpacecraftState;
21  import org.orekit.time.FieldAbsoluteDate;
22  
23  /** Provider for additional derivatives.
24  *
25  * <p>
26  * In some cases users may need to integrate some problem-specific equations along with
27  * classical spacecraft equations of motions. One example is optimal control in low
28  * thrust where adjoint parameters linked to the minimized Hamiltonian must be integrated.
29  * Another example is formation flying or rendez-vous which use the Clohessy-Whiltshire
30  * equations for the relative motion.
31  * </p>
32  * <p>
33  * This interface allows users to add such equations to a {@link
34  * org.orekit.propagation.numerical.FieldNumericalPropagator numerical propagator} or a {@link
35  * org.orekit.propagation.semianalytical.dsst.FieldDSSTPropagator DSST propagator}. Users provide the
36  * equations as an implementation of this interface and register it to the propagator thanks to
37  * its {@link FieldAbstractIntegratedPropagator#addAdditionalDerivativesProvider(FieldAdditionalDerivativesProvider)}
38  * method. Several such objects can be registered with each numerical propagator, but it is
39  * recommended to gather in the same object the sets of parameters which equations can interact
40  * on each others states.
41  * </p>
42  * <p>
43  * This interface is the numerical (read not already integrated) counterpart of
44  * the {@link org.orekit.propagation.FieldAdditionalStateProvider} interface.
45  * It allows to append various additional state parameters to any {@link
46  * org.orekit.propagation.numerical.FieldNumericalPropagator numerical propagator} or {@link
47  * org.orekit.propagation.semianalytical.dsst.FieldDSSTPropagator DSST propagator}.
48  * </p>
49  * @see org.orekit.propagation.integration.FieldAbstractIntegratedPropagator
50  * @author Luc Maisonobe
51  * @since 11.1
52  * @param <T> type of the field elements
53  */
54  public interface FieldAdditionalDerivativesProvider<T extends CalculusFieldElement<T>> {
55  
56      /** Get the name of the additional derivatives (which will become state once integrated).
57       * @return name of the additional state (names containing "orekit"
58       * with any case are reserved for the library internal use)
59       */
60      String getName();
61  
62      /** Get the dimension of the generated derivative.
63       * @return dimension of the generated
64       */
65      int getDimension();
66  
67      /** Initialize the generator at the start of propagation.
68       * @param initialState initial state information at the start of propagation
69       * @param target       date of propagation
70       */
71      default void init(final FieldSpacecraftState<T> initialState, final FieldAbsoluteDate<T> target) {
72          // nothing by default
73      }
74  
75      /** Check if this provider should yield so another provider has an opportunity to add missing parts.
76       * <p>
77       * Decision to yield is often based on an additional state being {@link FieldSpacecraftState#hasAdditionalState(String)
78       * already available} in the provided {@code state} (but it could theoretically also depend on
79       * an additional state derivative being {@link FieldSpacecraftState#hasAdditionalStateDerivative(String)
80       * already available}, or any other criterion). If for example a provider needs the state transition
81       * matrix, it could implement this method as:
82       * </p>
83       * <pre>{@code
84       * public boolean yields(final FieldSpacecraftState<T> state) {
85       *     return !state.getAdditionalStates().containsKey("STM");
86       * }
87       * }</pre>
88       * <p>
89       * The default implementation returns {@code false}, meaning that derivative data can be
90       * {@link #combinedDerivatives(FieldSpacecraftState) computed} immediately.
91       * </p>
92       * @param state state to handle
93       * @return true if this provider should yield so another provider has an opportunity to add missing parts
94       * as the state is incrementally built up
95       */
96      default boolean yields(FieldSpacecraftState<T> state) {
97          return false;
98      }
99  
100     /** Compute the derivatives related to the additional state (and optionally main state increments).
101      * @param s current state information: date, kinematics, attitude, and
102      * additional states this equations depend on (according to the
103      * {@link #yields(FieldSpacecraftState) yields} method)
104      * @return computed combined derivatives, which may include some incremental
105      * coupling effect to add to main state derivatives
106      * @since 11.2
107      */
108     FieldCombinedDerivatives<T> combinedDerivatives(FieldSpacecraftState<T> s);
109 
110 }