teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
sascha@3177: public class InvExp
sascha@3177: extends      Function
sascha@3177: {
sascha@3177:     public static final Derivative DERIVATIVE =
sascha@3177:         new Derivative("W'(Q) = 1/(log(a)*(Q-b))") {
sascha@3177: 
sascha@3177:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3177:             instantiate(double [] parameters)
sascha@3177:         {
sascha@3177:             final double a = parameters[1];
sascha@3177:             final double b = parameters[2];
sascha@3177:             final double loga = Math.log(a);
sascha@3177: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3177:                 @Override
sascha@3177:                 public double value(double Q) {
sascha@3177:                     return 1d/(loga*(Q-a));
sascha@3177:                 }
sascha@3177:             };
sascha@3177:         }
sascha@3177:     };
sascha@3177: 
sascha@3177:     public static final Function INSTANCE = new InvExp();
sascha@3177: 
sascha@3177:     public InvExp() {
sascha@3177:         super(
sascha@3177:             "inv-exp",
sascha@3177:             "Q(W) = log((W-b)/m)/log(a)",
sascha@3177:             new String [] { "m", "a", "b" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double value(double W, double [] parameters) {
sascha@3177:         double m = parameters[0];
sascha@3177:         double a = parameters[1];
sascha@3177:         double b = parameters[2];
sascha@3177:         return Math.log((W-b)/m)/Math.log(a);
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double [] gradient(double Q, double [] parameters) {
sascha@3177:         double m = parameters[0];
sascha@3177:         double a = parameters[1];
sascha@3177:         double b = parameters[2];
sascha@3177:         double loga = Math.log(a);
sascha@3177:         return new double [] {
sascha@3177:             -1d/(loga*m),
sascha@3177:             -Math.log((Q-b)/m)/(a*loga*loga),
sascha@3177:             -1d/(loga*(Q-b))
sascha@3177:         };
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Derivative getDerivative() {
sascha@3177:         return DERIVATIVE;
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Function getInverse() {
sascha@3177:         return Exp.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :