I'm using ACM to define a pervaporation module. In this module I have 3 ports: Feed, Permeate, Retentate. I want to define the calculation method of Feed components. I already defined the "Feed as input molefractionport". And z(componentlist) is already existed in the molefractionport. I also defined z(componentlist) in my variables. 

To calculate the component concentration in different streams, I write Feed.z("A") = (1-stagecut)*Retentate.z("A")+stagecut*Permeate.z("A"); 

Then I compile my script, but the ACM told me :

"Error at position 1: "Feed" unexpected - bad syntax or (missing) punctuation"

I tried different methods, like define X, Y, Z as the componentlist in Retentate, Permeate, and Feed, then let them equals to Retentate.z, Permeate.z, and Feed.z, but the same error message still popup. 

Would anyone please tell me why does the error happen? Why I can not directly use the Feed.z, Retentate.z, or Permeate.z, which already defined in the ports?