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@2569: 
sascha@2569: public class LogLinear
sascha@2569: extends      Function
sascha@2569: {
sascha@3009:     public static final Derivative DERIVATIVE =
sascha@3009:         new Derivative("W'(Q) = a*m/(m*Q + b)") {
sascha@3009: 
sascha@3009:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3009:             instantiate(double [] parameters)
sascha@3009:         {
sascha@3009:             final double a = parameters[0];
sascha@3009:             final double m = parameters[1];
sascha@3009:             final double b = parameters[2];
sascha@3009: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3009:                 @Override
sascha@3009:                 public double value(double Q) {
sascha@3009:                     return a*m/(m*Q + b);
sascha@3009:                 }
sascha@3009:             };
sascha@3009:         }
sascha@3009:     };
sascha@3009: 
sascha@3178:     public static final Function INSTANCE = new LogLinear();
sascha@3178: 
sascha@2569:     public LogLinear() {
sascha@2569:         super(
sascha@2569:             "log-linear",
sascha@2569:             "W(Q) = a*ln(m*Q + b)",
sascha@2569:             new String [] { "a", "m", "b" });
sascha@2569:     }
sascha@2569: 
sascha@2569:     @Override
sascha@2569:     public double value(double x, double [] parameters) {
sascha@2569:         return parameters[0]*Math.log(parameters[1]*x + parameters[2]);
sascha@2569:     }
sascha@2569: 
sascha@2569:     @Override
sascha@2569:     public double [] gradient(double x, double [] parameters) {
sascha@3165:         double a = parameters[0];
sascha@3165:         double m = parameters[1];
sascha@3165:         double b = parameters[2];
sascha@3165: 
sascha@3165:         double lin = m*x + b;
sascha@3165: 
sascha@2569:         return new double [] {
sascha@3165:             Math.log(lin),
sascha@3165:             a*x / lin,
sascha@3165:             a / lin
sascha@2569:         };
sascha@2569:     }
sascha@3009: 
sascha@3009:     @Override
sascha@3009:     public Derivative getDerivative() {
sascha@3009:         return DERIVATIVE;
sascha@3009:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Function getInverse() {
sascha@3177:         return InvLogLinear.INSTANCE;
sascha@3177:     }
sascha@2569: }
sascha@2569: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :