expose mur in interface

Magnetodynamics/transfo.pro

@@ -23,6 +23,8 @@ DefineConstant[
     Name "Parameters/01Conductor type"}
   Freq = {1, Min 0, Max 1e3, Step 1,
     Name "Parameters/Frequency"}
+  mur_Core = {1000, Min 1, Max 10000, Step 1,
+    Name "Parameters/Core relative permeability"}
 ];
 
 Group {
@@ -50,7 +52,6 @@ Group {
 
 Function {
   mu0 = 4e-7*Pi;
-  mur_Core = 1000;
   mu[Air] = 1 * mu0;
   mu[Core] = mur_Core * mu0;
   mu[Coils] = 1 * mu0;