Finally the fix: https://github.com/dealii/dealii/pull/9466
Paras: Thanks a lot for the excellent testcase! I managed to make it
substantially smaller still, but it was a very good starting point to find
what is actually happening! I co-credited you with the fix.
Best
W.
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On 2/1/20 12:44 PM, Krishnakumar Gopalakrishnan wrote:
"_Two difficulties_ arise due to the _*zero pivots*_ in the bottom-right block
of the matrix.
1. Firstly, following a classical result from linear algebra, such matrices
are indefinite and the conjugate gradient solver cannot be app
On 2/1/20 8:25 AM, Krishnakumar Gopalakrishnan wrote:
*__*
Recalling that the above system matrix is the discretized version of the
original (continuous) PDEs, this corresponds to the assembly of the bilinear form:
(v,K−1u)
−(divv,p)
−(q,divu)
* Now, the top-left block M of the matrix oper
