[petsc-users] schurcomplement of a rectangular system

[Patrick Lacasse]

Hi,

  in my works, I'm computing a formula (involving an L2 projection) of the
form:

(D - M^{-1} N) n

where D,M and B are matrices and n is a vector.

Operator (D - M^{-1} N) appears to be the Schur complement of the system
( M   N )
(  I    D )
and it is convenient for me to use a Mat of type schurcomplement to compute
it.
However, my matrix D is not a square matrix (this system is not invertible,
it is rectangular).

Assertions in src/ksp/ksp/utils/schurm.c prohibit the use of
schurcomplement for rectangular system, but I can't figure where it is
needed by schurcomplement itself.
Could it be possible to remove those two assertions (see my patch)?


Patrick Lacasse
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