--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flys-artifacts/src/main/java/org/dive4elements/river/artifacts/math/fitting/InvPow.java	Thu Apr 25 12:06:39 2013 +0200
@@ -0,0 +1,72 @@
+package org.dive4elements.river.artifacts.math.fitting;
+
+public class InvPow
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("Q'(W) = ((W-d)/a)^(1/c)/(c*(W-d))") {
+
+        @Override
+        public org.dive4elements.river.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+                  double  a = parameters[0];
+            final double  c = parameters[1];
+            final double  d = parameters[2];
+            final double _1a = 1d/a;
+            final double _1c = 1d/c;
+
+            return new org.dive4elements.river.artifacts.math.Function() {
+                @Override
+                public double value(double W) {
+                    double Wd = W-d;
+                    return Math.pow(Wd*_1a, _1c)/(c*Wd);
+                }
+            };
+        }
+    };
+
+    public static final Function INSTANCE = new InvPow();
+
+    public InvPow() {
+        super(
+            "pow",
+            "Q(W) = ((W-d)/a)^(1/c)",
+            new String [] { "a", "c", "d" });
+    }
+
+    @Override
+    public double value(double W, double [] parameters) {
+        double a = parameters[0];
+        double c = parameters[1];
+        double d = parameters[2];
+        return Math.pow((W-d)/a, 1d/c);
+    }
+
+    @Override
+    public double [] gradient(double W, double [] parameters) {
+        double a = parameters[0];
+        double c = parameters[1];
+        double d = parameters[2];
+        double _1c = 1d/c;
+        double Wdac = Math.pow((W-d)/a, 1d/c);
+        double Wd = W-d;
+        return new double [] {
+            -Wdac/(a*c),
+            (Wdac*Math.log(Wd/a))/(c*c),
+            -Wdac/(c*Wd)
+        };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        // TODO: Implement me!
+        return null;
+    }
+
+    @Override
+    public Function getInverse() {
+        return Pow.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :