teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
sascha@3177: public class InvLogLinear
sascha@3177: extends      Function
sascha@3177: {
sascha@3181:     public static final Derivative DERIVATIVE =
sascha@3181:         new Derivative("Q'(W) = e^(W/a)/(a*m)") {
sascha@3181: 
sascha@3181:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3181:             instantiate(double [] parameters)
sascha@3181:         {
sascha@3181:             final double _1a = 1d/parameters[0];
sascha@3181:             final double _1am = 1d/(parameters[0] * parameters[1]);
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 Math.exp(W*_1a)*_1am;
sascha@3181:                 }
sascha@3181:             };
sascha@3181:         }
sascha@3181:     };
sascha@3177:     public static final Function INSTANCE = new InvLogLinear();
sascha@3177: 
sascha@3177:     public InvLogLinear() {
sascha@3181:         super(
sascha@3181:             "inv-log-linear",
sascha@3181:             "Q(W)=(e^(W/a)-b)/m",
sascha@3181:             new String [] { "a", "m", "b" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double value(double W, double [] parameters) {
sascha@3181:         double a = parameters[0];
sascha@3181:         double m = parameters[1];
sascha@3181:         double b = parameters[2];
sascha@3181:         return (Math.exp(W/a) - b)/m;
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3181:     public double [] gradient(double W, double [] parameters) {
sascha@3181:         double a   = parameters[0];
sascha@3181:         double m   = parameters[1];
sascha@3181:         double b   = parameters[2];
sascha@3181:         double eWa = Math.exp(W/a);
sascha@3181:         return new double [] {
sascha@3181:             -(W*eWa)/(a*a*m)
sascha@3181:             -(eWa-b)/(m*m),
sascha@3181:             -1/m
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 LogLinear.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :