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[Anders Logg <logg@xxxxxxxxx>]

This seems to be a bug in FFC. I simplified your example and get the 
same error with the following example:

  from numpy import square as sqr

  P1 = VectorElement("Lagrange", "triangle", 1)

  v = TestFunction(P1)
  f = Function(P1)

  L = (sqr(f[0].dx(0)) + sqr(f[1].dx(1))) * v[0] * dx

I'll see what I can do. I know who to ask... ;-)

/Anders


Jed Brown wrote:
> (It seems that the inline attachments were washed, sorry for the repost.)
>
> I am having trouble getting FFC to generate code for nonlinear stokes
> flow.  I realize that the fractional powers code is just not written,
> but I'm not sure why the other cases don't work.  Here is my form file:
>
> # Compile this form with FFC: ffc -l dolfin GlenStokes.form
> From numpy import square as sqr
>
> P2 = VectorElement("Lagrange", "triangle", 2)
> P1 = FiniteElement("Lagrange", "triangle", 1)
> TH = P2 + P1
>
> (v, q) = TestFunctions(TH)
> (u, p) = TrialFunctions(TH)
>
> (U, P) = Functions(TH)
> g = Function(P2)
>
> D2 = (sqr(U[0].dx(0)) + sqr(U[1].dx(1))
>       + 0.5 * sqr(U[0].dx(1) + U[1].dx(0)))
> dD2 = (2 * U[0].dx(0) * u[0].dx(0) + 2 * U[1].dx(1) * u[1].dx(1)
>        + (U[0].dx(1) + U[1].dx(0)) * (u[0].dx(1) + u[1].dx(0)))
>
> ## The *real* Glen Stokes form: powers are not yet implemented
> # n = 3
> # eta = D2 ** ((1 - n) / (2 * n))
> # deta = ((1 - n) / (2 * n)) * D2 ** ((1 - 3 * n) / (2 * n)) * dD2
> ## Only use sqrt and inverse: error `Cannot take square root of sum.'
> # eta = 1 / sqrt(D2)
> # deta = - 1 / (2 * sqrt(D2) * D2) * dD2
> ## Something simpler: error `Index does not appear exactly twice in term.'
> eta = D2
> deta = dD2
>
> ## Linearized form to be used with fixed point method.
> a = (eta * dot(grad(v), grad(u)) - div(v) * p + q * div(u)) * dx
> L = dot(v, g) * dx
>
> ## Newton's method form
> # a = (eta * dot(grad(v), grad(u)) - div(v) * p + q * div(u)
> #      + deta * dot(grad(v), grad(U))) * dx
> # L = (dot(v, g) - (eta * dot(grad(v), grad(U))
> #                   - div(v) * P + q * div(U)))
> #### EOF
>
> This generates
>
> $ ffc -l dolfin -d1 GlenStokes.form >& GlenStokes.out
> This is FFC, the FEniCS Form Compiler, version 0.4.1.
> For further information, go to http://www/fenics.org/ffc/.
>
> Preprocessing form file: GlenStokes.form --> GlenStokes.py
>
> Phase 1: Analyzing form
> -----------------------
>
>   Checking validity of form... ok
>   Reassigning form indices... done
>   Checking validity of form... ok
>   Simplifying form... Reassigning form indices...
>   done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   Reassigning form indices... done
>   done
>   Checking validity of form...
> Traceback (most recent call last):
>   File "/home/jed/usr/bin/ffc", line 180, in ?
>     sys.exit(main(sys.argv[1:]))
>   File "/home/jed/usr/bin/ffc", line 107, in main
>     execfile(outname, ns)
>   File "GlenStokes.py", line 48, in ?
>     compile([a, L, M, element], "GlenStokes", "tensor", "dolfin", {'blas': False, 'precision=': '15', 'optimize': False})
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/compiler.py", line 66, in compile
>     form_data = __compile_forms(forms, prefix, representation, language, options)
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/compiler.py", line 92, in __compile_forms
>     form_data = analyze_form(form)
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/compiler.py", line 183, in analyze_form
>     form_data = analyze(form)
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/analysis/analyze.py", line 42, in analyze
>     check_form(form)
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/analysis/checks.py", line 24, in check_form
>     check_completeness(form)
>   File "/home/jed/usr/lib/python2.4/site-packages/ffc/compiler/analysis/checks.py", line 62, in check_completeness
>     raise FormError, (m, "Index does not appear exactly twice in term.")
> ffc.common.exceptions.FormError
>
>
>
> Am I doing something wrong or is there work to be done so that FFC can
> compile these forms?
>
> Jed
>
>
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