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
43 /**
44 * A PolynomialCurve describes points along a polynomial function.
45 *
46 * @author Jacob M. Litman
47 */
48 public class PolynomialCurve extends FunctionDataCurve {
49
50 /** Coefficients of the polynomial curve. */
51 private final double[] coefficients;
52
53 /**
54 * Default constructor, assumes constant-width bins. Functional form will be a0 + a1x + a2x^2 +
55 * a3x^3 + ... + anx^n.
56 *
57 * @param x an array of double values.
58 * @param coefficients Lowest-order coefficients first
59 */
60 public PolynomialCurve(double[] x, double[] coefficients) {
61 this(x, false, coefficients);
62 }
63
64 /**
65 * Default constructor, assumes constant-width bins. Functional form will be a0 + a1x + a2x^2 +
66 * a3x^3 + ... + anx^n.
67 *
68 * @param x an array of double values.
69 * @param halfWidthEnds Specifies that first and last bins are half-width.l
70 * @param coefficients Lowest-order coefficients first
71 */
72 public PolynomialCurve(double[] x, boolean halfWidthEnds, double[] coefficients) {
73 int nPoints = x.length;
74 points = new double[nPoints];
75 this.coefficients = new double[coefficients.length];
76 arraycopy(coefficients, 0, this.coefficients, 0, coefficients.length);
77 this.halfWidthEnd = halfWidthEnds;
78
79 for (int i = 0; i < points.length; i++) {
80 points[i] = polynomialAt(x[i]);
81 }
82 lb = x[0];
83 ub = x[nPoints - 1];
84 this.x = new double[x.length];
85 arraycopy(x, 0, this.x, 0, x.length);
86 }
87
88 /** {@inheritDoc} */
89 @Override
90 public double fX(double x) {
91 return polynomialAt(x);
92 }
93
94 /** {@inheritDoc} */
95 @Override
96 public double integralAt(double x) {
97 double total = 0;
98 for (int i = 0; i < coefficients.length; i++) {
99 double val = 1.0 / ((double) i + 1);
100 val *= coefficients[i];
101 for (int j = 0; j <= i; j++) {
102 val *= x;
103 }
104 total += val;
105 }
106 return total;
107 }
108
109 /** {@inheritDoc} */
110 @Override
111 public String toString() {
112 StringBuilder sb = new StringBuilder("Polynomial curve of degree ");
113 sb.append(coefficients.length)
114 .append(
115 format(
116 " with %d points from lower bound %9.3g and upper bound %9.3g",
117 points.length, lb, ub));
118 if (halfWidthEnd) {
119 sb.append(" and half-width start/end bins");
120 }
121 sb.append(".\nCoefficients: ");
122 if (coefficients.length > 0) {
123 sb.append(coefficients[0]);
124 }
125 for (int i = 1; i < coefficients.length; i++) {
126 sb.append(",").append(coefficients[i]);
127 }
128
129 return sb.toString();
130 }
131
132 // Private, non-overrideable method for use in the constructor.
133 private double polynomialAt(double x) {
134 double total = 0.0;
135 for (int i = 0; i < coefficients.length; i++) {
136 double val = coefficients[i];
137 for (int j = 0; j < i; j++) {
138 val *= x;
139 }
140 total += val;
141 }
142 return total;
143 }
144 }