--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flys-artifacts/src/main/java/org/dive4elements/river/artifacts/math/fitting/LogLinear.java	Thu Apr 25 12:06:39 2013 +0200
@@ -0,0 +1,65 @@
+package org.dive4elements.river.artifacts.math.fitting;
+
+public class LogLinear
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("W'(Q) = a*m/(m*Q + b)") {
+
+        @Override
+        public org.dive4elements.river.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double a = parameters[0];
+            final double m = parameters[1];
+            final double b = parameters[2];
+
+            return new org.dive4elements.river.artifacts.math.Function() {
+                @Override
+                public double value(double Q) {
+                    return a*m/(m*Q + b);
+                }
+            };
+        }
+    };
+
+    public static final Function INSTANCE = new LogLinear();
+
+    public LogLinear() {
+        super(
+            "log-linear",
+            "W(Q) = a*ln(m*Q + b)",
+            new String [] { "a", "m", "b" });
+    }
+
+    @Override
+    public double value(double x, double [] parameters) {
+        return parameters[0]*Math.log(parameters[1]*x + parameters[2]);
+    }
+
+    @Override
+    public double [] gradient(double x, double [] parameters) {
+        double a = parameters[0];
+        double m = parameters[1];
+        double b = parameters[2];
+
+        double lin = m*x + b;
+
+        return new double [] {
+            Math.log(lin),
+            a*x / lin,
+            a / lin
+        };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        return DERIVATIVE;
+    }
+
+    @Override
+    public Function getInverse() {
+        return InvLogLinear.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :