teichmann@5831: package org.dive4elements.river.artifacts.math.fitting;
sascha@3100: 
sascha@3100: public class SQPow
sascha@3100: extends      Function
sascha@3100: {
sascha@3100:     public static final Derivative DERIVATIVE =
sascha@3104:         new Derivative("S'(Q) = a*b*Q^(b-1)") {
sascha@3100: 
sascha@3100:         @Override
teichmann@5831:         public org.dive4elements.river.artifacts.math.Function
sascha@3100:             instantiate(double [] parameters)
sascha@3100:         {
sascha@3100:             final double a = parameters[0];
sascha@3100:             final double b = parameters[1];
sascha@3100: 
teichmann@5831:             return new org.dive4elements.river.artifacts.math.Function() {
sascha@3100:                 @Override
sascha@3100:                 public double value(double Q) {
sascha@3100:                     return a*b*Math.pow(Q, b-1);
sascha@3100:                 }
sascha@3100:             };
sascha@3100:         }
sascha@3100:     };
sascha@3100: 
sascha@3178:     public static final Function INSTANCE = new SQPow();
sascha@3178: 
sascha@3100:     public SQPow() {
sascha@3100:         super(
sascha@3100:             "sq-pow",
sascha@3100:             "S(Q) = a*Q^b",
sascha@3100:             new String [] { "a", "b" });
sascha@3100:     }
sascha@3100: 
sascha@3100:     @Override
sascha@3100:     public double value(double x, double [] parameters) {
sascha@3100:         return parameters[0]*Math.pow(x, parameters[1]);
sascha@3100:     }
sascha@3100: 
sascha@3100:     @Override
sascha@3100:     public double [] gradient(double q, double [] parameters) {
sascha@3100:         double a   = parameters[0];
sascha@3100:         double b   = parameters[1];
sascha@3100:         double q_b = Math.pow(q, b);
sascha@3100:         return new double [] {
sascha@3100:             q_b,
sascha@3100:             a*q_b*Math.log(q),
sascha@3100:         };
sascha@3100:     }
sascha@3100: 
sascha@3100:     @Override
sascha@3100:     public Derivative getDerivative() {
sascha@3100:         return DERIVATIVE;
sascha@3100:     }
sascha@3177: 
sascha@3177:     @Override
sascha@3177:     public Function getInverse() {
sascha@3177:         return InvSQPow.INSTANCE;
sascha@3177:     }
sascha@3100: }
sascha@3100: // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :