Hi to everybody!

I want to model a Mos transistor using a table model. I've saved my data in an external file "dati_mos.txt".
Then I recall it with the instructions:

Code:

parameter string model_file = ".\dati_mos.txt";
I(D,S) <+ $table_model(V(G,S), V(D,S), model_file, "3L,3L"); 

When I compile it, an error occour:

In file /home/xxx/xxx/xxx/table_model.vams line     27:
I(D,S) <+ $table_model(V(G,S), V(D,S), model_file, "3L,3L");
          ^
[Error] Unknown system function $table_model
Error: (valog) Compilation: Analysis failed.

How can I resolve it?
Many thanks!