### Inverse of piecewise constant of the second-rank tensor

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Dear FEniCS community,

I have a question if one of the coefficients is piecewise constant of the second-rank tensor, and in the left-hand side of the equation, I have to inverse this coefficient as you can see in the third line as `mu/k`. How should I accomplish this? Should I inverse it before put it in a0?

```
KM = TensorFunctionSpace(mesh, "DG", 0)
k = Function(KM)
a0 = inner(2*mu_l*strain(u)+lmbda_l*div(u)*I-alpha*p*I,sym(grad(y)))*dx\
+ div(v)*q*dx\
+ mu/k*inner(v,phi)*dx\
- p*div(phi)*dx
```

Thank you very much for your time.

Meen

Community: FEniCS Project

### 1 Answer

3

If you want to take the inverse of A_ij where A is a tensor of rank 2 with indices ij, then you should use

inv(A)

or

as_tensor( inv(A)[i,j] ... )

in your formulation.

Best, Emek

inv(A)

or

as_tensor( inv(A)[i,j] ... )

in your formulation.

Best, Emek

Thank you very much, Emek!!!

written
10 days ago by
Teeratorn Kadeethum

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