1 // ******************************************************************************
2 //
3 // Title: Force Field X.
4 // Description: Force Field X - Software for Molecular Biophysics.
5 // Copyright: Copyright (c) Michael J. Schnieders 2001-2024.
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 /**
41 * A LinearDerivativeSwitch interpolates between 0 and 1 vi f(x) = 2*x - x^2.
42 *
43 * <p>The derivative is then linear in x: f'(x) = 2 - 2*x
44 *
45 * <p>Limiting behavior is given by: f(0) = 0, f(1) = 1, f'(0) = 2, f'(1) = 0.
46 *
47 * @author Michael J. Schnieders
48 */
49 public class LinearDerivativeSwitch implements UnivariateSwitchingFunction {
50
51 /** Constructor for the LinearDerivativeSwitch. */
52 public LinearDerivativeSwitch() {
53 }
54
55 /** {@inheritDoc} */
56 @Override
57 public boolean constantOutsideBounds() {
58 return false;
59 }
60
61 /** {@inheritDoc} */
62 @Override
63 public double firstDerivative(double x) throws IllegalArgumentException {
64 return 2.0 - 2.0 * x;
65 }
66
67 /** {@inheritDoc} */
68 @Override
69 public int getHighestOrderZeroDerivative() {
70 return 0;
71 }
72
73 /** {@inheritDoc} */
74 @Override
75 public double getOneBound() {
76 return 1;
77 }
78
79 /** {@inheritDoc} */
80 @Override
81 public double getZeroBound() {
82 return 0;
83 }
84
85 /** {@inheritDoc} */
86 @Override
87 public double nthDerivative(double x, int order) throws IllegalArgumentException {
88 if (order < 1) {
89 throw new IllegalArgumentException("Order must be >= 1");
90 }
91 return switch (order) {
92 case 1 -> firstDerivative(x);
93 case 2 -> secondDerivative(x);
94 default -> 0;
95 };
96 }
97
98 /** {@inheritDoc} */
99 @Override
100 public double secondDerivative(double x) throws IllegalArgumentException {
101 return -2.0;
102 }
103
104 /** {@inheritDoc} */
105 @Override
106 public boolean symmetricToUnity() {
107 return false;
108 }
109
110 @Override
111 public String toString() {
112 return "Polynomial switch of form f(x) = 2x - x^2";
113 }
114
115 /** {@inheritDoc} */
116 @Override
117 public boolean validOutsideBounds() {
118 return false;
119 }
120
121 /** {@inheritDoc} */
122 @Override
123 public double valueAt(double x) throws IllegalArgumentException {
124 return 2 * x - (x * x);
125 }
126 }