Dear all,
This is a similar question related to a post two years ago:
https://groups.google.com/g/dealii/c/1L6gLFtvTCo/m/frIyTDXbBwAJ
I am developing a fractional time stepping algorithm based on an operator
split. Basically, I can obtain the following monolithc system after the
finite element discretization:
* A B 0 u1
b1*
*tangent matrix = B C D , solution = u2, RHS = b2*
* E 0 F u3
b3*
where *tangent matrix* is a 3 by 3 BlockSparseMatrix.
During a time interval, I want to use the first split operator
*A B * u1 = b1 *to solve* u1 *and* u2.*
*B C u2 b2*
Then, plug the solved u1 and u2 into the second split operator
*F * u3 = b3*
where *F* contains the information of the newly solved *u1* and *u2*.
My question is, is there an easy way now to extract the sparse matrices *A,
B, B, C* to form a new BlockSparseMatrix, something like the following:
new BlockSparseMatrix = *tangent matrix*.block(0, 0), *tangent
matrix*.block(0,
1)
*tangent matrix*.block(1,
0), *tangent matrix*.block(1, 1)
Thank you
Tao
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