Hi

  Yes, I take the following settings in the models.xml file in order to get site operator Sy

   <SITEOPERATOR name="Sx" complex="true" site"i">

   <PARAMETER name="I" complex="true"/>

   (Splus(i)-Sminus(i))/2/I

   </SITEOPERATOR> 

    This setting resembles the standard setting of the site operator Sx in models.xml file

   <SITEOPERATOR name="Sx" site"i">

   (Splus(i)+Sminus(i))/2

   </SITEOPERATOR> 

 But the error message (cannot evaluate I) reappears, and make the running stop.

  As a novice I don't  know how to set it in details. Could you help me? Thanks