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[Chong Luo <luo.chong@xxxxxxxxx>]

I saw in FFC manual that in the .form files, we can "define new operators
using standard Python syntax".

 I want to define the covariance of a matrix A, so I wrote the following code:

def cov(A):
    B = A
    for i in range(1, 3):
        for j in range(1, 3):
            B[i][j] = A[(i+2)%3][(j+2)%3]*A[(i+1)%3][(j+1)%3] \
                     -A[(i+2)%3][(j+1)%3]*A[(i+1)%3][(j+2)%3]

a(F) = dot(grad(v), mult(cov(F), grad(u)))*dx
L = dot(v, f)*dx + dot(v('+'), g('+'))*dS

However, I got this error: 
  File "Elasticity.py", line 36
    a(F) = dot(grad(v), mult(cov(F), grad(u)))*dx
SyntaxError: can't assign to function call


Any idea how to make it work? Similarly I'd like to implement 
the operator d^2(det(F))/dF^2, because these are needed in
incompressible nonlinear elasticity.

Thank you!

Best,

Chong Luo
PhD student in Applied Math
University of Minnesota








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