[petsc-users] what is the restriction for PCMG, and how to control it?

[Ed Bueler]

Dear PETSc --

This is most embarassing, but somehow I can't see it in the docs.

Regarding defaults for DMDA and PCMG, for the fine-to-coarse restriction,
does -pc_type mg use the adjoint of interpolation?   (I.e. "full
weighting," at least up to a constant.)  Or is an injection used?

I see that in src/dm/impls/da/dainterp.c, both (Q1,Q0) interpolation and
some injection are _implemented_ for DMDA.  But I don't see what is used by
default, or how to control it at the command line.  Asking for options
related to my question is a bit of a dead end.  For example, in
src/snes/examples/tutorials/,
  ./ex5 -da_refine 3 -pc_type mg -help | grep XX
returns nothing at all for XX=injection,restriction,interpolation.

Would a new option
  -pc_mg_restriction_type transpose|injection
make sense?

Thanks,

Ed


-- 
Ed Bueler
Dept of Math and Stat and Geophysical Institute
University of Alaska Fairbanks
Fairbanks, AK 99775-6660
301C Chapman
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