[petsc-users] Fw: Multigrid Vcycle.

[Abdul Hanan Sheikh]

Thanks for early response Jed!, 
>
>I fixed outer Krylov as PREONLY so it does not use any vectors (I guess). 
>Standard Vcycle includes 1 pre and 1 post smoothing. 
>
>KSP-Richardson + PC-Jacobi are ingredients for pre-smoothing and  post smoothing. 
>To my understanding, 2 Vectors are used by KSP Richardson + 1 Vector is used by PC-Jacobi 
>at pre and post smoothing. This makes 6 vectors at each level and for 5 levels, they should be 30! 
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>Do I think right ? 
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>Further hint to make PCMG more memory-efficient is appreciated. 
>with warm regard, Abdul 
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>>________________________________
>> From: Jed Brown <jedbrown at mcs.anl.gov>
>>To: Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>; PETSc users list <petsc-users at mcs.anl.gov> 
>>Sent: Thursday, 24 May 2012, 21:22
>>Subject: Re: [petsc-users] Multigrid Vcycle.
>> 
>>
>>On Thu, May 24, 2012 at 2:14 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>>
>>Dear all, 
>>>
>>>I am quit beginner in PETSc. 
>>>
>>>I wrote a code for multigrid Vcycle (as preconditioer) by following the instructions on manual page. 
>>>
>>>I want to see how much memory a Vcycle allocates by default in terms of number of matrices and vectors. 
>>>
>>>I made a try to see by comparing with jacobi preconditioner, which surely allocates 1 vector ONLY. 
>>>
>>>It turns out that a VCycle for FIVE (5) levels including coarsest level allocates memory for 53 vectors and 
>>>
>>>subsequently it destroys too.
>>
>>
>>Some of those vectors are very small due to being on the coarse level. There are also the vectors used by the outer Krylov method.
>> 
>>
>>>
>>>Is it normal ?? 
>>>
>>>
>>>
>>>
>>>
>>>Thanks in advance, 
>>>
>>>Abdul
>>>
>>
>>
>>
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