--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/math/fitting/Log.java	Thu Apr 25 15:23:37 2013 +0200
@@ -0,0 +1,57 @@
+package org.dive4elements.river.artifacts.math.fitting;
+
+public class Log
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("W'(Q) = m/(Q+b)") {
+
+        @Override
+        public org.dive4elements.river.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double m = parameters[0];
+            final double b = parameters[1];
+
+            return new org.dive4elements.river.artifacts.math.Function() {
+                @Override
+                public double value(double Q) {
+                    return m/(Q+b);
+                }
+            };
+        }
+    };
+
+    public static final Function INSTANCE = new Log();
+
+    public Log() {
+        super("log",  "W(Q) = m*ln(Q + b)", new String [] { "m", "b" });
+    }
+
+    @Override
+    public double value(double x, double [] parameters) {
+        return parameters[0]*Math.log(x + parameters[1]);
+    }
+
+    @Override
+    public double [] gradient(double x, double [] parameters) {
+        double m = parameters[0];
+        double b = parameters[1];
+        double b_x = b + x;
+        return new double [] {
+            Math.log(b_x),
+            m/b_x
+        };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        return DERIVATIVE;
+    }
+
+    @Override
+    public Function getInverse() {
+        return InvLog.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :