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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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9    *   http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
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16   */
17  package org.orekit.propagation.integration;
18  
19  import org.orekit.propagation.SpacecraftState;
20  import org.orekit.time.AbsoluteDate;
21  
22  /** Provider for additional derivatives.
23   *
24   * <p>
25   * In some cases users may need to integrate some problem-specific equations along with
26   * classical spacecraft equations of motions. One example is optimal control in low
27   * thrust where adjoint parameters linked to the minimized Hamiltonian must be integrated.
28   * Another example is formation flying or rendez-vous which use the Clohessy-Whiltshire
29   * equations for the relative motion.
30   * </p>
31   * <p>
32   * This interface allows users to add such equations to a {@link
33   * org.orekit.propagation.numerical.NumericalPropagator numerical propagator} or a {@link
34   * org.orekit.propagation.semianalytical.dsst.DSSTPropagator DSST propagator}. Users provide the
35   * equations as an implementation of this interface and register it to the propagator thanks to
36   * its {@link AbstractIntegratedPropagator#addAdditionalDerivativesProvider(AdditionalDerivativesProvider)}
37   * method. Several such objects can be registered with each numerical propagator, but it is
38   * recommended to gather in the same object the sets of parameters which equations can interact
39   * on each others states.
40   * </p>
41   * <p>
42   * This interface is the numerical (read not already integrated) counterpart of
43   * the {@link org.orekit.propagation.AdditionalDataProvider} interface.
44   * It allows to append various additional state parameters to any {@link
45   * org.orekit.propagation.numerical.NumericalPropagator numerical propagator} or {@link
46   * org.orekit.propagation.semianalytical.dsst.DSSTPropagator DSST propagator}.
47   * </p>
48   * @see org.orekit.propagation.integration.AbstractIntegratedPropagator
49   * @author Luc Maisonobe
50   * @since 11.1
51   */
52  public interface AdditionalDerivativesProvider {
53  
54      /** Get the name of the additional derivatives (which will become state once integrated).
55       * @return name of the additional state (names containing "orekit"
56       * with any case are reserved for the library internal use)
57       */
58      String getName();
59  
60      /** Get the dimension of the generated derivative.
61       * @return dimension of the generated
62       */
63      int getDimension();
64  
65      /** Initialize the generator at the start of propagation.
66       * @param initialState initial state information at the start of propagation
67       * @param target       date of propagation
68       */
69      default void init(final SpacecraftState initialState, final AbsoluteDate target) {
70          // nothing by default
71      }
72  
73      /** Check if this provider should yield so another provider has an opportunity to add missing parts.
74       * <p>
75       * Decision to yield is often based on an additional state being {@link SpacecraftState#hasAdditionalData(String)
76       * already available} in the provided {@code state} (but it could theoretically also depend on
77       * an additional state derivative being {@link SpacecraftState#hasAdditionalStateDerivative(String)
78       * already available}, or any other criterion). If for example a provider needs the state transition
79       * matrix, it could implement this method as:
80       * </p>
81       * <pre>{@code
82       * public boolean yields(final SpacecraftState state) {
83       *     return !state.getAdditionalStates().containsKey("STM");
84       * }
85       * }</pre>
86       * <p>
87       * The default implementation returns {@code false}, meaning that derivative data can be
88       * {@link #combinedDerivatives(SpacecraftState) computed} immediately.
89       * </p>
90       * @param state state to handle
91       * @return true if this provider should yield so another provider has an opportunity to add missing parts
92       * as the state is incrementally built up
93       */
94      default boolean yields(final SpacecraftState state) {
95          return false;
96      }
97  
98      /** Compute the derivatives related to the additional state (and optionally main state increments).
99       * @param s current state information: date, kinematics, attitude, and
100      * additional states this equations depend on (according to the
101      * {@link #yields(SpacecraftState) yields} method)
102      * @return computed combined derivatives, which may include some incremental
103      * coupling effect to add to main state derivatives
104      * @since 11.2
105      */
106     CombinedDerivatives combinedDerivatives(SpacecraftState s);
107 
108 }