SNESSetUp() and matrix-free options

[Jed Brown]

Barry Smith wrote:

> It is always possible someone has two options that conflict with each
> other in the options database. This is suppose to generate an
> error. and the only solution is for user to change one of them.

My point is that -snes_mf and -snes_mf_operator are not really that
different.  If there is only one option, then the options database will
only know about the last one and there is no conflict.  For example, I
could put -pc_type lu in .petscrc, and then put -pc_type asm on the
command line without conflicts.  I am suggesting making sure that there
is only one way to select the snes_mf variant on the command line in
order to eliminate unnecessary possible conflicts.

Jed

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