1   /* Copyright 2022-2026 Romain Serra
2    * Licensed to CS GROUP (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
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
15   * limitations under the License.
16   */
17  package org.orekit.utils;
18  
19  import java.util.function.ToDoubleFunction;
20  
21  import org.hipparchus.CalculusFieldElement;
22  import org.orekit.propagation.FieldSpacecraftState;
23  import org.orekit.propagation.SpacecraftState;
24  
25  /** Interface representing a scalar function depending only on {@link SpacecraftState} or its field counterpart.
26   * @author Romain Serra
27   * @since 14.0
28   */
29  @FunctionalInterface
30  public interface ExtendedStateScalarFunction {
31  
32      /** Evaluate the function.
33       * @param state spacecraft state as the sole free parameter of the function.
34       * @return scalar value of the function
35       */
36      double value(SpacecraftState state);
37  
38      /** Evaluate the Field function.
39       * @param fieldState spacecraft state as the sole free parameter of the function.
40       * @param <T> field type
41       * @return scalar value of the function
42       */
43      default <T extends CalculusFieldElement<T>> T value(final FieldSpacecraftState<T> fieldState) {
44          return fieldState.getMass().getField().getZero().newInstance(value(fieldState.toSpacecraftState()));
45      }
46  
47      /**
48       * Create instance from pure double function.
49       * @param function function of double
50       * @return extended function
51       */
52      static ExtendedStateScalarFunction of(final ToDoubleFunction<SpacecraftState> function) {
53          return function::applyAsDouble;
54      }
55  }