--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flys-artifacts/src/main/java/org/dive4elements/river/artifacts/math/fitting/InvSQPow.java	Thu Apr 25 12:06:39 2013 +0200
@@ -0,0 +1,64 @@
+package org.dive4elements.river.artifacts.math.fitting;
+
+public class InvSQPow
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("Q'(S) = (S/a)^(1/b)/(b*S)") {
+
+        @Override
+        public org.dive4elements.river.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double _1a = 1d/parameters[0];
+            final double   b = parameters[1];
+            final double _1b = 1d/b;
+
+            return new org.dive4elements.river.artifacts.math.Function() {
+                @Override
+                public double value(double S) {
+                    return Math.pow(S*_1a, _1b)/(b*S);
+                }
+            };
+        }
+    };
+    public static final Function INSTANCE = new InvSQPow();
+
+    public InvSQPow() {
+        super(
+            "inv-sq-pow",
+            "Q(S) = Q=(S/a)^(1/b)",
+            new String [] { "a", "b" });
+    }
+
+    @Override
+    public double value(double S, double [] parameters) {
+        double a = parameters[0];
+        double b = parameters[1];
+        return Math.pow(S/a, 1d/b);
+    }
+
+    @Override
+    public double [] gradient(double S, double [] parameters) {
+        double a     = parameters[0];
+        double b     = parameters[1];
+        double Sa    = S/a;
+        double _1b   = 1d/b;
+        double eSa1b = Math.pow(Sa, _1b);
+        return new double [] {
+            -eSa1b/(a*b),
+            -(eSa1b*Math.log(Sa))/(b*b)
+        };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        return DERIVATIVE;
+    }
+
+    @Override
+    public Function getInverse() {
+        return SQPow.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :