teichmann@5863: /* Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
teichmann@5863:  * Software engineering by Intevation GmbH
teichmann@5863:  *
teichmann@5863:  * This file is Free Software under the GNU AGPL (>=v3) 
teichmann@5863:  * and comes with ABSOLUTELY NO WARRANTY! Check out the
teichmann@5863:  * documentation coming with Dive4Elements River for details. 
teichmann@5863:  */
teichmann@5863: 
teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
sascha@3177: public class InvLog
sascha@3177: extends      Function
sascha@3177: {
sascha@3177:     public static final Derivative DERIVATIVE =
sascha@3177:         new Derivative("Q'(W) = exp(W/m)/m") {
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 _1m = 1d / parameters[0];
sascha@3177: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3177:                 @Override
sascha@3177:                 public double value(double W) {
sascha@3177:                     return Math.exp(W*_1m)*_1m;
sascha@3177:                 }
sascha@3177:             };
sascha@3177:         }
sascha@3177:     };
sascha@3177: 
sascha@3177:     public static final Function INSTANCE = new InvLog();
sascha@3177: 
sascha@3177:     public InvLog() {
sascha@3177:         super("inv-log",  "Q(W) = e^(W/m) - b", new String [] { "m", "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 b = parameters[1];
sascha@3177:         return Math.exp(w/m) - b;
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public double [] gradient(double w, double [] parameters) {
sascha@3177:         double m   = parameters[0];
sascha@3177:         double b   = parameters[1];
sascha@3177:         double ewm = Math.exp(w/m);
sascha@3177:         return new double [] { -w*ewm/(m*m), -1 };
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 Log.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :