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 InvSQPow
sascha@3177: extends      Function
sascha@3177: {
sascha@3181:     public static final Derivative DERIVATIVE =
sascha@3181:         new Derivative("Q'(S) = (S/a)^(1/b)/(b*S)") {
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   b = parameters[1];
sascha@3181:             final double _1b = 1d/b;
sascha@3181: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3181:                 @Override
sascha@3181:                 public double value(double S) {
sascha@3181:                     return Math.pow(S*_1a, _1b)/(b*S);
sascha@3181:                 }
sascha@3181:             };
sascha@3181:         }
sascha@3181:     };
sascha@3177:     public static final Function INSTANCE = new InvSQPow();
sascha@3177: 
sascha@3177:     public InvSQPow() {
sascha@3181:         super(
sascha@3181:             "inv-sq-pow",
sascha@3181:             "Q(S) = Q=(S/a)^(1/b)",
sascha@3181:             new String [] { "a", "b" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3181:     public double value(double S, double [] parameters) {
sascha@3181:         double a = parameters[0];
sascha@3181:         double b = parameters[1];
sascha@3181:         return Math.pow(S/a, 1d/b);
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3181:     public double [] gradient(double S, double [] parameters) {
sascha@3181:         double a     = parameters[0];
sascha@3181:         double b     = parameters[1];
sascha@3181:         double Sa    = S/a;
sascha@3181:         double _1b   = 1d/b;
sascha@3181:         double eSa1b = Math.pow(Sa, _1b);
sascha@3181:         return new double [] {
sascha@3181:             -eSa1b/(a*b),
sascha@3181:             -(eSa1b*Math.log(Sa))/(b*b)
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 SQPow.INSTANCE;
sascha@3177:     }
sascha@3177: }
sascha@3177: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :