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.integrate;
39
40 import static java.lang.String.format;
41 import static java.lang.System.arraycopy;
42 import static org.apache.commons.math3.util.FastMath.cos;
43 import static org.apache.commons.math3.util.FastMath.sin;
44
45 /**
46 * A SinWave describes points along a sine wave of f(x) = a*sin(jx).
47 *
48 * @author Jacob M. Litman
49 */
50 public class SinWave extends FunctionDataCurve {
51
52 /**
53 * Magnitude.
54 */
55 private final double a;
56 /**
57 * Periodicity.
58 */
59 private final double n;
60 /**
61 * Inverse periodicity.
62 */
63 private final double nInverse;
64
65 /**
66 * Constructs f(x) = a*sin(nx).
67 *
68 * @param x an array of {@link double} objects.
69 * @param a magnitude.
70 * @param n periodicity.
71 */
72 public SinWave(double[] x, double a, double n) {
73 this(x, false, a, n);
74 }
75
76 /**
77 * Constructs f(x) = a*sin(nx).
78 *
79 * @param x an array of {@link double} objects.
80 * @param halfWidthEnds Use half-width start and end bins.
81 * @param a magnitude.
82 * @param n periodicity.
83 */
84 public SinWave(double[] x, boolean halfWidthEnds, double a, double n) {
85 int nPoints = x.length;
86 points = new double[nPoints];
87 this.a = a;
88 this.n = n;
89 nInverse = 1.0 / n;
90 this.halfWidthEnd = halfWidthEnds;
91
92 for (int i = 0; i < points.length; i++) {
93 points[i] = sinAt(x[i]);
94 }
95 lb = x[0];
96 ub = x[nPoints - 1];
97 this.x = new double[x.length];
98 arraycopy(x, 0, this.x, 0, x.length);
99 }
100
101 /**
102 * {@inheritDoc}
103 */
104 @Override
105 public double fX(double x) {
106 return sinAt(x);
107 }
108
109 /**
110 * {@inheritDoc}
111 */
112 @Override
113 public double integralAt(double x) {
114 return -1 * a * nInverse * cos(n * x);
115 }
116
117 /**
118 * {@inheritDoc}
119 */
120 @Override
121 public String toString() {
122 StringBuilder sb = new StringBuilder("Sine wave f(x) = ");
123 sb.append(a).append("*sin(").append(n).append("x)");
124 sb.append(
125 format(
126 " with %d points from lower bound %9.3g and upper bound %9.3g", points.length, lb, ub));
127 if (halfWidthEnd) {
128 sb.append(" and half-width start/end bins");
129 }
130
131 return sb.toString();
132 }
133
134 // Private, non-overrideable method for use in the constructor.
135 private double sinAt(double x) {
136 return a * sin(n * x);
137 }
138 }