--- a/flys-artifacts/src/main/java/de/intevation/flys/artifacts/math/fitting/InvLogLinear.java	Tue Jun 26 10:45:33 2012 +0000
+++ b/flys-artifacts/src/main/java/de/intevation/flys/artifacts/math/fitting/InvLogLinear.java	Tue Jun 26 10:54:12 2012 +0000
@@ -3,28 +3,57 @@
 public class InvLogLinear
 extends      Function
 {
+    public static final Derivative DERIVATIVE =
+        new Derivative("Q'(W) = e^(W/a)/(a*m)") {
+
+        @Override
+        public de.intevation.flys.artifacts.math.Function
+            instantiate(double [] parameters)
+        {
+            final double _1a = 1d/parameters[0];
+            final double _1am = 1d/(parameters[0] * parameters[1]);
+
+            return new de.intevation.flys.artifacts.math.Function() {
+                @Override
+                public double value(double W) {
+                    return Math.exp(W*_1a)*_1am;
+                }
+            };
+        }
+    };
     public static final Function INSTANCE = new InvLogLinear();
 
     public InvLogLinear() {
-        // TODO: Implement me!
+        super(
+            "inv-log-linear",
+            "Q(W)=(e^(W/a)-b)/m",
+            new String [] { "a", "m", "b" });
     }
 
     @Override
     public double value(double W, double [] parameters) {
-        // TODO: Implement me!
-        return 0d;
+        double a = parameters[0];
+        double m = parameters[1];
+        double b = parameters[2];
+        return (Math.exp(W/a) - b)/m;
     }
 
     @Override
-    public double [] gradient(double Q, double [] parameters) {
-        // TODO: Implement me!
-        return null;
+    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() {
-        // TODO: Implement me!
-        return null;
+        return DERIVATIVE;
     }
 
     @Override