
From:  Konstantinos Poulios 
Subject:  Re: [Getfemusers] divergence of stress tensor 
Date:  Fri, 19 Jan 2018 19:16:54 +0100 
Dear Yves,Thank you for your reply!We expressed the divergence of stress tensor with respect to the variable u. In the _expression_, we have something like Grad(Trace(Grad_u)), and Trace(Hess_u). When assembling these terms with GetFEM, there is an error in assembly string. I tried to assembly separately these two terms. Both did not work.For the first term Grad(Trace(Grad_u)), I think the error comes from the fact that, in GetFEM, we can only use Grad operator with a variable, i.e., Grad_u, Grad_Test_u, etc. Therefore, we can not write directly Grad(Trace(Grad_u)). Is it right?
For the second term Trace(Hess_u), I think the error comes from the Trace operator, since in the GetFEM documentation, it is stated that Trace operator is used for a square matrix. In our case, since u is a vector field, Hess_u is a tensor of order 3. Can we use Trace operator in assembly string for a tensor of order 3?
Thank you in advance for your reply.Best regards,Phuoc
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