teichmann@5863: /* Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
teichmann@5863:  * Software engineering by Intevation GmbH
teichmann@5863:  *
teichmann@5994:  * This file is Free Software under the GNU AGPL (>=v3)
teichmann@5863:  * and comes with ABSOLUTELY NO WARRANTY! Check out the
teichmann@5994:  * documentation coming with Dive4Elements River for details.
teichmann@5863:  */
teichmann@5863: 
teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3177: 
d@9643: public class InvSQPow extends Function {
d@9643:     public static final Derivative DERIVATIVE = new Derivative("Q'(S) = (S/a)^(1/b)/(b*S)") {
sascha@3181: 
sascha@3181:         @Override
d@9643:         public org.dive4elements.river.artifacts.math.Function instantiate(final double[] parameters) {
d@9643:             final double _1a = 1d / parameters[0];
d@9643:             final double b = parameters[1];
d@9643:             final double _1b = 1d / b;
sascha@3181: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3181:                 @Override
d@9643:                 public double value(final double S) {
d@9643:                     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() {
d@9643:         super("inv-special", "Q(S) = Q=(S/a)^(1/b)", new String[] { "a", "b" });
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
d@9643:     public double value(final double S, final double[] parameters) {
d@9643:         final double a = parameters[0];
d@9643:         final double b = parameters[1];
d@9643:         return Math.pow(S / a, 1d / b);
sascha@3177:     }
sascha@3177: 
sascha@3177:     @Override
d@9643:     public double[] gradient(final double S, final double[] parameters) {
d@9643:         final double a = parameters[0];
d@9643:         final double b = parameters[1];
d@9643:         final double Sa = S / a;
d@9643:         final double _1b = 1d / b;
d@9643:         final double eSa1b = Math.pow(Sa, _1b);
d@9643:         return new double[] { -eSa1b / (a * b), -(eSa1b * Math.log(Sa)) / (b * b) };
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 :