teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
sascha@3177: public class InvQuad
sascha@3177: extends      Function
sascha@3177: {
sascha@3181:     public static final Derivative DERIVATIVE =
sascha@3181:         new Derivative("Q'(W) = 1/sqrt(4*n*(W-b)+m^2)") {
sascha@3181: 
sascha@3181:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3181:             instantiate(double [] parameters)
sascha@3181:         {
sascha@3181:                   double n  = parameters[0];
sascha@3181:                   double m  = parameters[1];
sascha@3181:             final double b  = parameters[2];
sascha@3181:             final double n4 = 4d*n;
sascha@3181:             final double mm = m*m;
sascha@3181: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3181:                 @Override
sascha@3181:                 public double value(double W) {
sascha@3181:                     return 1d/Math.sqrt(n4*(W-b)+mm);
sascha@3181:                 }
sascha@3181:             };
sascha@3181:         }
sascha@3181:     };
sascha@3181: 
sascha@3177:     public static final Function INSTANCE = new InvQuad();
sascha@3177: 
sascha@3177:     public InvQuad() {
sascha@3181:         super(
sascha@3181:             "inv-quad",
sascha@3181:             "(sqrt(4*n*W-4*b*n+m^2)-m)/(2*n)",
sascha@3181:             new String [] { "n", "m", "b" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double value(double W, double [] parameters) {
sascha@3181:         double n = parameters[0];
sascha@3181:         double m = parameters[1];
sascha@3181:         double b = parameters[2];
sascha@3181:         return (Math.sqrt(4d*n*(W - b) + m*m)-m)/(2d*n);
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3181:     public double [] gradient(double W, double [] parameters) {
sascha@3181:         double n  = parameters[0];
sascha@3181:         double m  = parameters[1];
sascha@3181:         double b  = parameters[2];
sascha@3181:         double Wb = W-b;
sascha@3181:         double sn4Wb = Math.sqrt(4d*n*Wb + m*m);
sascha@3181:         return new double [] {
sascha@3181:             Wb/(n*sn4Wb)-(sn4Wb-m)/(2d*n*n),
sascha@3181:             (m/sn4Wb-1d)/(2d*n),
sascha@3181:             -1d/sn4Wb
sascha@3181:         };
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Derivative getDerivative() {
sascha@3181:         return DERIVATIVE;
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Function getInverse() {
sascha@3178:         return Quad.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :