whether do I need to consider the symmetric preconditioner when using CG?

[Yujie]

hi, everyone

I know there are three types of preconditioners, that is left, split and
right preconditioners? When I use CG method in PETSc, whether do I need to
consider select one type of preconditioner? Whether do different types
affect the performance of preconditioned CG? thanks a lot.

Regards,
Yujie
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