[petsc-users] An advice on a linear system solution

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:
> Fieldsplit block preconditioners can be used on this type of matrix, but
> success obviously depends on the
> analytic character of the operators.  In particular, if we assume that we
> have great PCs for the diagonal,
> then B is the most important variable, and we need to know what the Schur
> complement
>
>    B^T  A^{-1} B or equiv B^T C^{-1} B

Matt means

  D - B^T A^{-1} B

or

  A - B C^{-1} B^T
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