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