[Libmesh-users] Non-symmetric constrained element matrices in case of recursive constraints

[Jonas B. <jon...@ep...>]

Dear all,

What I found out so far is that the problem in my example is related to having a cycle in the constraints. If there are no cycles in the constraints, all constraints can be resolved before they are applied so that each constrained_dof_index (which is a row index) never appears as a constraining dof (which is a column index). In this case, the matrix C has a zero column at the constrained_dof_index, so that C^T*K*C has zero rows and columns for all  constrained_dof_indices. This means that inserting unit rows for the constrained_dof_indices afterwards produces a symmetric constraint matrix. In case of a cycle, the columns of C at the constrained_dof_indices can also be non-zero as in my example so that the final result is non-symmetric.

I ran into that issue in opt mode, so I wonder if there is any error checking in place that looks for cycles in the constraints?

Best,
Jonas