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;
39
40 import ffx.numerics.Potential;
41 import ffx.potential.bonded.LambdaInterface;
42 import ffx.potential.parameters.ForceField;
43
44 /**
45 * FiniteDifference
46 *
47 * @version 1.0
48 */
49 public class FiniteDifferenceUtils {
50
51 /**
52 * Compute dE/dL using finite differences.
53 *
54 * @param potential The potential to compute the energy of.
55 * @param lambdaInterface The lambda interface to use.
56 * @param forceField The force field to use.
57 * @return The computed dE/dL.
58 */
59 public static double computedEdL(Potential potential, LambdaInterface lambdaInterface, ForceField forceField) {
60 // Small optimization to only create the x array once.
61 int n = potential.getNumberOfVariables();
62 double[] x = new double[n];
63 potential.getCoordinates(x);
64
65 double finiteDifferenceStepSize = forceField.getDouble("FD_DLAMBDA", 0.001);
66 boolean twoSidedFiniteDifference = forceField.getBoolean("FD_TWO_SIDED", true);
67
68 double currentLambda = lambdaInterface.getLambda();
69 double width = finiteDifferenceStepSize;
70 double ePlus;
71 double eMinus;
72
73 if (twoSidedFiniteDifference) {
74 if (currentLambda + finiteDifferenceStepSize > 1.0) {
75 lambdaInterface.setLambda(currentLambda - finiteDifferenceStepSize);
76 eMinus = potential.energy(x);
77 lambdaInterface.setLambda(currentLambda);
78 ePlus = potential.energy(x);
79 } else if (currentLambda - finiteDifferenceStepSize < 0.0) {
80 lambdaInterface.setLambda(currentLambda + finiteDifferenceStepSize);
81 ePlus = potential.energy(x);
82 lambdaInterface.setLambda(currentLambda);
83 eMinus = potential.energy(x);
84 } else {
85 // Two sided finite difference estimate of dE/dL.
86 lambdaInterface.setLambda(currentLambda + finiteDifferenceStepSize);
87 ePlus = potential.energy(x);
88 lambdaInterface.setLambda(currentLambda - finiteDifferenceStepSize);
89 eMinus = potential.energy(x);
90 width *= 2.0;
91 lambdaInterface.setLambda(currentLambda);
92 }
93 } else {
94 // One-sided finite difference estimates of dE/dL
95 if (currentLambda + finiteDifferenceStepSize > 1.0) {
96 lambdaInterface.setLambda(currentLambda - finiteDifferenceStepSize);
97 eMinus = potential.energy(x);
98 lambdaInterface.setLambda(currentLambda);
99 ePlus = potential.energy(x);
100 } else {
101 lambdaInterface.setLambda(currentLambda + finiteDifferenceStepSize);
102 ePlus = potential.energy(x);
103 lambdaInterface.setLambda(currentLambda);
104 eMinus = potential.energy(x);
105 }
106 }
107
108 // Compute the finite difference derivative.
109 double dEdL = (ePlus - eMinus) / width;
110
111 // logger.info(format(" getdEdL currentLambda: CL=%8.6f L=%8.6f dEdL=%12.6f", currentLambda,
112 // lambda, dEdL));
113 return dEdL;
114
115 }
116
117 }