[petsc-users] Multigrid Vcycle.

[Abdul Hanan Sheikh]

Dear all, 
Are you seeing the memory used by those vectors being a significant part of the overall memory usage of the program? 

To this question, I think yes. 
Is it also normal, number of vectors is dependent upon how many levels used ?  
I experienced this. When I increase levels in PCMG, number of vectors used (created and destroyed) increases. 

Thanks, 
Abdul .


>________________________________
> 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, 22:06
>Subject: Re: [petsc-users] Multigrid Vcycle.
> 
>
>On Thu, May 24, 2012 at 2:29 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk> wrote:
>
>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! 
>>
>
>
>DMSetUp_DA_nD creates and destroys two vectors as part of its set up process. There is also a scaling vector associated with restriction (so that restriction and prolongation can use the same matrix, which they usually do), including a momentary work vector used to compute the scaling. So many of those vectors are not alive at once.
>
>
>Are you seeing the memory used by those vectors being a significant part of the overall memory usage of the program?
>
>
>Barry, 
> 
>
>>
>>Do I think right ? 
>>
>>Further hint to make PCMG more memory-efficient is appreciated. 
>>with warm regard, Abdul 
>>
>>
>>
>>
>>
>>>________________________________
>>> 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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