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