Barry Smith bsmith at
Mon Jun 8 13:52:42 CDT 2009

    The GMRES coded in PETSc does NOT support right preconditioning.  
The code that is there was not intended for right preconditioning and  
was never "fixed up" to support right preconditioning.

    The FGMRES code was written for right preconditioning (but the  
FGMRES algorithm itself does not support left preconditioning.)

    Yes, it would be nice if someone worked through the GMRES code (it  
is ugly) and added support for right preconditioning but no one has  
had the initiative. When I want to run with GMRES and right  
preconditioning for some test I just use FGMES.


On Jun 8, 2009, at 1:46 PM, Lisandro Dalcin wrote:

> Barry,
> In the commit below you disabled PC_RIGHT from GMRES... Could you
> remember me what was wrong with GMRES+PC_RIGHT ?
> changeset:   11545:81b50d76a9c5
> user:        bsmith at
> date:        Wed Jan 16 11:12:45 2008 -0600
> summary:     added error check for right preconditioner on GMRES
> -- 
> Lisandro Dalcín
> ---------------
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> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
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