[petsc-users] DGMRES Right preconditioner

[Desire NUENTSA WAKAM]

Hi Gong,
You do not need to modify the source code for the right preconditioning.
The additional preconditioner (say M_D^{-1}) is built from the 
approximate eigenvalues of  M^{-1}A  or AM^{-1}.
  Hence you are solving either M_D^{-1}M_{-1}Ax = M_D^{-1}M_{-1}b or 
AM^{-1}M^{-1}_Dy = b for x  = M^{-1}M^{-1}_Dy

Thanks
Desire

On 10/03/2011 03:03 PM, Barry Smith wrote:
>    Desire,
>
>      Any suggestions? Does this make sense?
>
>     Thanks
>
>     Barry
>
> On Oct 3, 2011, at 4:47 AM, Gong Ding wrote:
>
>    
>> Hi,
>> I had installed petsc-3.2, which has a new deflated GMRES solver.
>> It seems the deflation procedure provides addtional precondition on top of GMRES.
>>
>> However, it seems the deflation was implemented as first right preconditioner:
>>
>> if (ksp->pc_side == PC_LEFT) {
>>                 /* Apply the first preconditioner */
>>                 ierr = KSP_PCApplyBAorAB (ksp,VEC_VV (it), VEC_TEMP,VEC_TEMP_MATOP);
>>                 CHKERRQ (ierr);
>>                 /* Then apply Deflation as a preconditioner */
>>                 ierr=KSPDGMRESApplyDeflation (ksp, VEC_TEMP, VEC_VV (1+it));
>>                 CHKERRQ (ierr);
>>             } else if (ksp->pc_side == PC_RIGHT) {
>>                 ierr=KSPDGMRESApplyDeflation (ksp, VEC_VV (it), VEC_TEMP);
>>                 CHKERRQ (ierr);
>>                 ierr=KSP_PCApplyBAorAB (ksp, VEC_TEMP, VEC_VV (1+it), VEC_TEMP_MATOP);
>>                 CHKERRQ (ierr);
>>             }
>>
>> Since a "fixed" external preconditoner M such as ILU or my own PC will be used,
>> I want the deflation apply on AM^-1. As a result, the update of deflation preconditioner will not
>> affect the fixed preconditioner M. How should I modify the source code?
>>
>>
>> Gong Ding
>>
>>
>>
>>
>>
>>
>>
>>      
>
>    
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