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3    * contributor license agreements.  See the NOTICE file distributed with
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5    * CS licenses this file to You under the Apache License, Version 2.0
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11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
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14   * See the License for the specific language governing permissions and
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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  */
53  public interface FieldAdditionalDerivativesProvider<T extends CalculusFieldElement<T>> {
54  
55      /** Get the name of the additional derivatives (which will become state once integrated).
56       * @return name of the additional state (names containing "orekit"
57       * with any case are reserved for the library internal use)
58       */
59      String getName();
60  
61      /** Get the dimension of the generated derivative.
62       * @return dimension of the generated
63       */
64      int getDimension();
65  
66      /** Initialize the generator at the start of propagation.
67       * @param initialState initial state information at the start of propagation
68       * @param target       date of propagation
69       */
70      default void init(final FieldSpacecraftState<T> initialState, final FieldAbsoluteDate<T> target) {
71          // nothing by default
72      }
73  
74      /** Check if this provider should yield so another provider has an opportunity to add missing parts.
75       * <p>
76       * Decision to yield is often based on an additional state being {@link FieldSpacecraftState#hasAdditionalState(String)
77       * already available} in the provided {@code state} (but it could theoretically also depend on
78       * an additional state derivative being {@link FieldSpacecraftState#hasAdditionalStateDerivative(String)
79       * already available}, or any other criterion). If for example a provider needs the state transition
80       * matrix, it could implement this method as:
81       * </p>
82       * <pre>{@code
83       * public boolean yield(final FieldSpacecraftState<T> state) {
84       *     return !state.getAdditionalStates().containsKey("STM");
85       * }
86       * }</pre>
87       * <p>
88       * The default implementation returns {@code false}, meaning that derivative data can be
89       * {@link #derivatives(FieldSpacecraftState) computed} immediately.
90       * </p>
91       * @param state state to handle
92       * @return true if this provider should yield so another provider has an opportunity to add missing parts
93       * as the state is incrementally built up
94       */
95      default boolean yield(FieldSpacecraftState<T> state) {
96          return false;
97      }
98  
99      /** Compute the derivatives related to the additional state parameters.
100      * @param s current state information: date, kinematics, attitude, and
101      * additional states this equations depend on (according to the
102      * {@link #yield(FieldSpacecraftState) yield} method)
103      * @return computed derivatives
104      */
105     T[] derivatives(FieldSpacecraftState<T> s);
106 
107 }