New user NGSolve coding issue


I am new to NGSolve, I am trying to write the bilinear form and the linear form for the Stokes problem, but I get an error as follows
f = LinearForm(X)
f +=InnerProduct(rhs,v)dx #Use the code to calc the righthandside
f +=InnerProduct(U_ex,v)ita/hds(skeleton=True)
f +=InnerProduct(grad(v)n,U_ex)
—> 33 f +=InnerProductb[/b][b]
[/b]dx #Use the code to calc the righthandside 34 f +=InnerProductb[/b][b]
[/b]ita/h*dsb[/b] 35 f +=InnerProductb[/b]
NgException: In MakeLinearFormIntegrator: must not have TrialFunction
v is a test function not a trial function
Any help would be really appreciated
Thank you

How is U_ex, ita, h defined? Does it contain a trialfunction?

No, U_ex is the manufactured solution. The trial function is u and is not in any of the functions included in the linear form.

Could you maybe provide a minimal working example of your problem?