--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/math/fitting/InvLogLinear.java	Thu Apr 25 15:23:37 2013 +0200
@@ -0,0 +1,64 @@
+package org.dive4elements.river.artifacts.math.fitting;
+
+public class InvLogLinear
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("Q'(W) = e^(W/a)/(a*m)") {
+
+        @Override
+        public org.dive4elements.river.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double _1a = 1d/parameters[0];
+            final double _1am = 1d/(parameters[0] * parameters[1]);
+
+            return new org.dive4elements.river.artifacts.math.Function() {
+                @Override
+                public double value(double W) {
+                    return Math.exp(W*_1a)*_1am;
+                }
+            };
+        }
+    };
+    public static final Function INSTANCE = new InvLogLinear();
+
+    public InvLogLinear() {
+        super(
+            "inv-log-linear",
+            "Q(W)=(e^(W/a)-b)/m",
+            new String [] { "a", "m", "b" });
+    }
+
+    @Override
+    public double value(double W, double [] parameters) {
+        double a = parameters[0];
+        double m = parameters[1];
+        double b = parameters[2];
+        return (Math.exp(W/a) - b)/m;
+    }
+
+    @Override
+    public double [] gradient(double W, double [] parameters) {
+        double a   = parameters[0];
+        double m   = parameters[1];
+        double b   = parameters[2];
+        double eWa = Math.exp(W/a);
+        return new double [] {
+            -(W*eWa)/(a*a*m)
+            -(eWa-b)/(m*m),
+            -1/m
+        };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        return DERIVATIVE;
+    }
+
+    @Override
+    public Function getInverse() {
+        return LogLinear.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :