--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/math/fitting/InvLog.java	Tue Jun 26 06:33:37 2012 +0000
@@ -0,0 +1,56 @@
+package de.intevation.flys.artifacts.math.fitting;
+
+public class InvLog
+extends      Function
+{
+    public static final Derivative DERIVATIVE =
+        new Derivative("Q'(W) = exp(W/m)/m") {
+
+        @Override
+        public de.intevation.flys.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double _1m = 1d / parameters[0];
+
+            return new de.intevation.flys.artifacts.math.Function() {
+                @Override
+                public double value(double W) {
+                    return Math.exp(W*_1m)*_1m;
+                }
+            };
+        }
+    };
+
+    public static final Function INSTANCE = new InvLog();
+
+    public InvLog() {
+        super("inv-log",  "Q(W) = e^(W/m) - b", new String [] { "m", "b" });
+    }
+
+    @Override
+    public double value(double w, double [] parameters) {
+        double m = parameters[0];
+        double b = parameters[1];
+        return Math.exp(w/m) - b;
+    }
+
+    @Override
+    public double [] gradient(double w, double [] parameters) {
+        double m   = parameters[0];
+        double b   = parameters[1];
+        double ewm = Math.exp(w/m);
+        return new double [] { -w*ewm/(m*m), -1 };
+    }
+
+    @Override
+    public Derivative getDerivative() {
+        return DERIVATIVE;
+    }
+
+    @Override
+    public Function getInverse() {
+        return Log.INSTANCE;
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :
+