[petsc-users] petsc KLU

[Abhyankar, Shrirang G.]

Romain,
   I added the KLU interface to PETSc last year hearing the hype about
KLU¹s performance from several power system folks. I must say that I¹m
terribly disappointed! I did some performance testing of KLU on power grid
problems (power flow application) last year and I got a similar
performance that you report (PETSc is 2-4 times faster than KLU). I also
clocked the time spent in PETSc¹s SuiteSparse interface for KLU for
operations other than factorization and it was very minimal. The fastest
linear solver combination that I found was PETSc¹s LU solver + AMD
ordering from the SuiteSparse package (-pc_factor_mat_ordering_type amd).
Don¹t try MUMPS and SuperLU ‹ they are terribly slow.

Shri


From:  hong zhang <hzhang at mcs.anl.gov>
Date:  Monday, August 17, 2015 at 10:08 AM
To:  Romain Thomas <R.Thomas at tudelft.nl>
Cc:  "petsc-users at mcs.anl.gov" <petsc-users at mcs.anl.gov>
Subject:  Re: [petsc-users] petsc KLU


>Romain:
>Do you mean small sparse sequential 200 by 200 matrices?
>Petsc LU might be better than external LU packages because it implements
>simple LU algorithm and we took good care on data accesing (I've heard
>same observations). You may try 'qmd' matrix ordering for power grid
>simulation. 
>I do not have experience on SuiteSparse. Testing MUMPS is worth it as
>well.
>
>Hong
>
>
>Hi
>Thank you for your answer. I was asking help because I find LU
>factorization 2-3 times faster than KLU. According to my problem size
>(200*200) and type (power system simulation), I should get almost the
>same computation time. Is it true to think that? Is the
> difference of time due to the interface between PETSc and SuiteSparse?
>Thank you,
>Romain
>
>-----Original Message-----
>From: Barry Smith [mailto:bsmith at mcs.anl.gov]
>Sent: vrijdag 14 augustus 2015 17:31
>To: Romain Thomas
>Cc: Matthew Knepley; petsc-users at mcs.anl.gov
>Subject: Re: [petsc-users] petsc KLU
>
>
>   You should call
>
>    MatGetFactor(mat,MATSOLVERKLU,MAT_FACTOR_LU,&fact);
>
>  then call
>
>> MatLUFactorNumeric(Mat fact,Mat mat,const MatFactorInfo *info)
>> MatLUFactorSymbolic(Mat fact,Mat mat,IS row,IS col,const MatFactorInfo
>> *info) MatLUFactor(Mat mat,IS row,IS col,const MatFactorInfo *info)
>
>   This routines correctly internally call the appropriate
>MatLUFactorNumeric_KLU() etc for you because you passed MATSOLVERKLU
>above.
>   There is no reason to (and it won't work) to call
>
>> MatLUFactorNumeric_KLU(Mat F,Mat A,const MatFactorInfo *info)
>> MatLUFactorSymbolic_KLU(Mat F,Mat A,IS r,IS c,const MatFactorInfo
>> *info) MatGetFactor_seqaij_klu(Mat A,MatFactorType ftype,Mat *F)
>
>directly.
>
>  Barry
>
>> On Aug 14, 2015, at 10:07 AM, Romain Thomas <R.Thomas at tudelft.nl> wrote:
>>
>> Hi,
>> Thank you for your answer.
>> My problem is a bit more complex. During the simulation (³real time²),
>>I need to upgrade at each time step the matrix A and the
>>MatassemblyBegin and MatassemblyEnd take time and so, in order to avoid
>>these functions, I don¹t use ksp or pc. I prefer to use
> the functions MatLUFactorNumeric, MatLUFactorSymbolic and MatLUFactor.
>And so, I want to know if there is similar functions for KLU. (I tried
>for Cholesky and, iLU and it works well).
>> Best regards,
>> Romain
>>
>>
>> From: Matthew Knepley [mailto:knepley at gmail.com]
>> Sent: vrijdag 14 augustus 2015 16:41
>> To: Romain Thomas
>> Cc: petsc-users at mcs.anl.gov
>> Subject: Re: [petsc-users] petsc KLU
>>
>> On Fri, Aug 14, 2015 at 9:23 AM, Romain Thomas <R.Thomas at tudelft.nl>
>>wrote:
>> Dear PETSc users,
>>
>> I would like to know if I can replace the following functions
>>
>> MatLUFactorNumeric(Mat fact,Mat mat,const MatFactorInfo *info)
>> MatLUFactorSymbolic(Mat fact,Mat mat,IS row,IS col,const MatFactorInfo
>> *info) MatLUFactor(Mat mat,IS row,IS col,const MatFactorInfo *info)
>>
>> by
>>
>> MatLUFactorNumeric_KLU(Mat F,Mat A,const MatFactorInfo *info)
>> MatLUFactorSymbolic_KLU(Mat F,Mat A,IS r,IS c,const MatFactorInfo
>> *info) MatGetFactor_seqaij_klu(Mat A,MatFactorType ftype,Mat *F)
>>
>> in my code for the simulation of electrical power systems? (I
>> installed the package SuiteSparse)
>>
>> Why would you do that? It already works with the former code. In fact,
>> you should really just use
>>
>>   KSPCreate(comm, &ksp)
>>   KSPSetOperator(ksp, A, A);
>>   KSPSetFromOptions(ksp);
>>   KSPSolve(ksp, b, x);
>>
>> and then give the options
>>
>>   -ksp_type preonly -pc_type lu -pc_mat_factor_package suitesparse
>>
>> This is no advantage to using the Factor language since subsequent
>> calls to
>> KSPSolve() will not refactor.
>>
>>    Matt
>>
>> Thank you,
>> Best regards,
>> Romain
>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>>experiments is infinitely more interesting than any results to which
>>their experiments lead.
>> -- Norbert Wiener
>
>
>
>
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