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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 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 {@link double} objects.
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 {@link double} objects.
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 }