1 // ******************************************************************************
2 //
3 // Title: Force Field X.
4 // Description: Force Field X - Software for Molecular Biophysics.
5 // Copyright: Copyright (c) Michael J. Schnieders 2001-2025.
6 //
7 // This file is part of Force Field X.
8 //
9 // Force Field X is free software; you can redistribute it and/or modify it
10 // under the terms of the GNU General Public License version 3 as published by
11 // the Free Software Foundation.
12 //
13 // Force Field X is distributed in the hope that it will be useful, but WITHOUT
14 // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
15 // FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
16 // details.
17 //
18 // You should have received a copy of the GNU General Public License along with
19 // Force Field X; if not, write to the Free Software Foundation, Inc., 59 Temple
20 // Place, Suite 330, Boston, MA 02111-1307 USA
21 //
22 // Linking this library statically or dynamically with other modules is making a
23 // combined work based on this library. Thus, the terms and conditions of the
24 // GNU General Public License cover the whole combination.
25 //
26 // As a special exception, the copyright holders of this library give you
27 // permission to link this library with independent modules to produce an
28 // executable, regardless of the license terms of these independent modules, and
29 // to copy and distribute the resulting executable under terms of your choice,
30 // provided that you also meet, for each linked independent module, the terms
31 // and conditions of the license of that module. An independent module is a
32 // module which is not derived from or based on this library. If you modify this
33 // library, you may extend this exception to your version of the library, but
34 // you are not obligated to do so. If you do not wish to do so, delete this
35 // exception statement from your version.
36 //
37 // ******************************************************************************
38 package ffx.potential.bonded;
39
40 /**
41 * The LambdaInterface should be implemented by potential energy terms that can accept a lambda
42 * value from [0 .. 1] that defines a twice differentiable path between states 0 and 1.
43 *
44 * @author Michael J. Schnieders
45 * @since 1.0
46 */
47 public interface LambdaInterface {
48
49 /**
50 * Returns true if dUdL is guaranteed to be zero at 0 and 1. Default implementation is to return
51 * false.
52 *
53 * @return True if dUdL is guaranteed 0 at endpoints.
54 */
55 default boolean dEdLZeroAtEnds() {
56 return false;
57 }
58
59 /**
60 * Get the current value of the state variable.
61 *
62 * @return state
63 * @since 1.0
64 */
65 double getLambda();
66
67 /**
68 * Set the current value of the state variable. May be ignored if lambda is not being applied.
69 *
70 * @param lambda a double.
71 * @since 1.0
72 */
73 void setLambda(double lambda);
74
75 /**
76 * Get the 2nd partial derivative of the energy with respect to lambda.
77 *
78 * @return d2EdL2
79 * @since 1.0
80 */
81 double getd2EdL2();
82
83 /**
84 * Get the partial derivative of the energy with respect to lambda.
85 *
86 * @return dEdL
87 * @since 1.0
88 */
89 double getdEdL();
90
91 /**
92 * Get the gradient of dEdL with respect to each parameter.
93 *
94 * @param gradient - A double array of length the number of parameters in the model (commonly 3 *
95 * number of atoms).
96 * @since 1.0
97 */
98 void getdEdXdL(double[] gradient);
99 }