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.openmm;
39
40 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_create;
41 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_destroy;
42 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_getErrorTolerance;
43 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_getMaximumStepSize;
44 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_setErrorTolerance;
45 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_setMaximumStepSize;
46 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_step;
47 import static edu.uiowa.jopenmm.OpenMMLibrary.OpenMM_VariableVerletIntegrator_stepTo;
48
49 /**
50 * This class implements a Verlet integrator with variable time stepping.
51 * The integrator automatically adjusts the step size to maintain a specified
52 * error tolerance, making it suitable for systems with widely varying time scales.
53 * <p>
54 * Unlike the standard Verlet integrator which uses a fixed step size, this
55 * variable step size algorithm monitors the local truncation error and adjusts
56 * the step size accordingly. This can lead to more efficient integration for
57 * systems where different parts evolve on different time scales.
58 */
59 public class VariableVerletIntegrator extends Integrator {
60
61 /**
62 * Create a VariableVerletIntegrator.
63 *
64 * @param errorTol The error tolerance for adaptive step sizing.
65 */
66 public VariableVerletIntegrator(double errorTol) {
67 super(OpenMM_VariableVerletIntegrator_create(errorTol));
68 }
69
70 /**
71 * Destroy the integrator.
72 */
73 @Override
74 public void destroy() {
75 if (pointer != null) {
76 OpenMM_VariableVerletIntegrator_destroy(pointer);
77 pointer = null;
78 }
79 }
80
81 /**
82 * Get the error tolerance for adaptive step sizing.
83 *
84 * @return The error tolerance.
85 */
86 public double getErrorTolerance() {
87 return OpenMM_VariableVerletIntegrator_getErrorTolerance(pointer);
88 }
89
90 /**
91 * Get the maximum step size the integrator is allowed to use (in ps).
92 *
93 * @return The maximum step size.
94 */
95 public double getMaximumStepSize() {
96 return OpenMM_VariableVerletIntegrator_getMaximumStepSize(pointer);
97 }
98
99 /**
100 * Set the error tolerance for adaptive step sizing.
101 *
102 * @param tol The error tolerance.
103 */
104 public void setErrorTolerance(double tol) {
105 OpenMM_VariableVerletIntegrator_setErrorTolerance(pointer, tol);
106 }
107
108 /**
109 * Set the maximum step size the integrator is allowed to use (in ps).
110 *
111 * @param size The maximum step size.
112 */
113 public void setMaximumStepSize(double size) {
114 OpenMM_VariableVerletIntegrator_setMaximumStepSize(pointer, size);
115 }
116
117 /**
118 * Advance a simulation through time by taking a series of time steps.
119 *
120 * @param steps The number of time steps to take.
121 */
122 public void step(int steps) {
123 OpenMM_VariableVerletIntegrator_step(pointer, steps);
124 }
125
126 /**
127 * Advance the simulation by integrating until a specified time is reached.
128 *
129 * @param time The time to which the simulation should be advanced (in ps).
130 */
131 public void stepTo(double time) {
132 OpenMM_VariableVerletIntegrator_stepTo(pointer, time);
133 }
134 }