[petsc-users] GAMG and zero pivots follow up

[Jed Brown]

Mark Adams <mfadams at lbl.gov> writes:
>> Yikes! I did not check that. Why do we have PRECONDITIONED as the default
>> for CG?

That is the preconditioned norm of the residual.  I.e.,

  || M^{-1} (A x - b) ||_2

> The two norm of the residual (ie, natural, right?) is not monotone either
> in CG.

"natural" is CG's energy norm, i.e.,

  || e ||_{M^{-1/2} A M^{-T/2}}
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