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.numerics.switching;
39
40 import static java.lang.String.format;
41
42 /**
43 * The ConstantSwitch returns a constant value for all input values x. This is useful for having a
44 * single code path that accommodates both "real" switching behavior and no switching behavior. The
45 * default value is 1.0.
46 *
47 * @author Jacob M. Litman
48 * @author Michael J. Schnieders
49 */
50 public class ConstantSwitch implements UnivariateSwitchingFunction {
51
52 private final double val;
53
54 /** Default constructor: constant 1.0 value. */
55 public ConstantSwitch() {
56 this(1.0);
57 }
58
59 /**
60 * Permits specification of a value.
61 *
62 * @param value Value this ConstantSwitch should maintain.
63 */
64 public ConstantSwitch(double value) {
65 this.val = value;
66 }
67
68 /** {@inheritDoc} */
69 @Override
70 public boolean constantOutsideBounds() {
71 return true;
72 }
73
74 /** {@inheritDoc} */
75 @Override
76 public double firstDerivative(double x) {
77 return 0.0;
78 }
79
80 /** {@inheritDoc} */
81 @Override
82 public int getHighestOrderZeroDerivative() {
83 return 1;
84 }
85
86 /** {@inheritDoc} */
87 @Override
88 public double getOneBound() {
89 return Double.NaN;
90 }
91
92 /** {@inheritDoc} */
93 @Override
94 public double getZeroBound() {
95 return Double.NaN;
96 }
97
98 /** {@inheritDoc} */
99 @Override
100 public double nthDerivative(double x, int order) throws IllegalArgumentException {
101 if (order < 0) {
102 throw new IllegalArgumentException(format(" Order must be > 0, was %d", order));
103 } else if (order == 0) {
104 return val;
105 }
106 return 0.0;
107 }
108
109 /** {@inheritDoc} */
110 @Override
111 public double secondDerivative(double x) {
112 return 0.0;
113 }
114
115 /** {@inheritDoc} */
116 @Override
117 public boolean symmetricToUnity() {
118 return true;
119 }
120
121 @Override
122 public String toString() {
123 return format(
124 "Constant-value f(x) = %f, with no switching behavior (i.e. a dummy switch)", val);
125 }
126
127 /** {@inheritDoc} */
128 @Override
129 public boolean validOutsideBounds() {
130 return false;
131 }
132
133 /** {@inheritDoc} */
134 @Override
135 public double valueAt(double x) throws IllegalArgumentException {
136 return val;
137 }
138 }