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17  package org.orekit.propagation.integration;
18  
19  import org.hipparchus.CalculusFieldElement;
20  import org.orekit.propagation.FieldAdditionalDataProvider;
21  import org.orekit.propagation.FieldSpacecraftState;
22  import org.orekit.time.FieldAbsoluteDate;
23  
24  /** Provider for additional derivatives.
25  *
26  * <p>
27  * In some cases users may need to integrate some problem-specific equations along with
28  * classical spacecraft equations of motions. One example is optimal control in low
29  * thrust where adjoint parameters linked to the minimized Hamiltonian must be integrated.
30  * Another example is formation flying or rendez-vous which use the Clohessy-Whiltshire
31  * equations for the relative motion.
32  * </p>
33  * <p>
34  * This interface allows users to add such equations to a {@link
35  * org.orekit.propagation.numerical.FieldNumericalPropagator numerical propagator} or a {@link
36  * org.orekit.propagation.semianalytical.dsst.FieldDSSTPropagator DSST propagator}. Users provide the
37  * equations as an implementation of this interface and register it to the propagator thanks to
38  * its {@link FieldAbstractIntegratedPropagator#addAdditionalDerivativesProvider(FieldAdditionalDerivativesProvider)}
39  * method. Several such objects can be registered with each numerical propagator, but it is
40  * recommended to gather in the same object the sets of parameters which equations can interact
41  * on each others states.
42  * </p>
43  * <p>
44  * This interface is the numerical (read not already integrated) counterpart of
45  * the {@link FieldAdditionalDataProvider} interface.
46  * It allows to append various additional state parameters to any {@link
47  * org.orekit.propagation.numerical.FieldNumericalPropagator numerical propagator} or {@link
48  * org.orekit.propagation.semianalytical.dsst.FieldDSSTPropagator DSST propagator}.
49  * </p>
50  * @see org.orekit.propagation.integration.FieldAbstractIntegratedPropagator
51  * @author Luc Maisonobe
52  * @since 11.1
53  * @param <T> type of the field elements
54  */
55  public interface FieldAdditionalDerivativesProvider<T extends CalculusFieldElement<T>> {
56  
57      /** Get the name of the additional derivatives (which will become state once integrated).
58       * @return name of the additional state (names containing "orekit"
59       * with any case are reserved for the library internal use)
60       */
61      String getName();
62  
63      /** Get the dimension of the generated derivative.
64       * @return dimension of the generated
65       */
66      int getDimension();
67  
68      /** Initialize the generator at the start of propagation.
69       * @param initialState initial state information at the start of propagation
70       * @param target       date of propagation
71       */
72      default void init(final FieldSpacecraftState<T> initialState, final FieldAbsoluteDate<T> target) {
73          // nothing by default
74      }
75  
76      /** Check if this provider should yield so another provider has an opportunity to add missing parts.
77       * <p>
78       * Decision to yield is often based on an additional state being {@link FieldSpacecraftState#hasAdditionalData(String)
79       * already available} in the provided {@code state} (but it could theoretically also depend on
80       * an additional state derivative being {@link FieldSpacecraftState#hasAdditionalStateDerivative(String)
81       * already available}, or any other criterion). If for example a provider needs the state transition
82       * matrix, it could implement this method as:
83       * </p>
84       * <pre>{@code
85       * public boolean yields(final FieldSpacecraftState<T> state) {
86       *     return !state.getAdditionalStates().containsKey("STM");
87       * }
88       * }</pre>
89       * <p>
90       * The default implementation returns {@code false}, meaning that derivative data can be
91       * {@link #combinedDerivatives(FieldSpacecraftState) computed} immediately.
92       * </p>
93       * @param state state to handle
94       * @return true if this provider should yield so another provider has an opportunity to add missing parts
95       * as the state is incrementally built up
96       */
97      default boolean yields(FieldSpacecraftState<T> state) {
98          return false;
99      }
100 
101     /** Compute the derivatives related to the additional state (and optionally main state increments).
102      * @param s current state information: date, kinematics, attitude, and
103      * additional states this equations depend on (according to the
104      * {@link #yields(FieldSpacecraftState) yields} method)
105      * @return computed combined derivatives, which may include some incremental
106      * coupling effect to add to main state derivatives
107      * @since 11.2
108      */
109     FieldCombinedDerivatives<T> combinedDerivatives(FieldSpacecraftState<T> s);
110 
111 }