My smooth progress with this awesome tool has hit a first barrier.

The attached linear stokes code works as is with the "VERSION 1" weak form.  Run simply as "python3 ./linflowstep.py".  The attached mesh file is read by default.

But with "grad()" replaced by "epsilon()", as recommended in the UFL manual*, which is VERSION 2, I get seg fault.  Slight modifications do or do not work according to mere value of the constant (see VERSION 3/4 ... weird).

Can you reproduce?  Any ideas?

I seek to use the strain rate tensor (= epsilon(u)) in a nonnewtonian stokes job, but this is blocking.

Thanks,

Ed

PS*  https://media.readthedocs.org/pdf/fenics-ufl/stable/fenics-ufl.pdf  page 23

PPS  Any advice for using a debugger on firedrake codes?  I am used to debugging PETSc C codes using gdb, but that is not working for me yet.

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