[Trilinos-Users] Inverse of a sparse matrix

[Martin Vymazal]

Hello Mike,

  thank you a lot for the hint. I'll try the solvers you mentioned.

  Martin Vymazal


Quoting "Heroux, Michael A" <maherou at sandia.gov>:

> Martin,
>
> The best way to compute the exact inverse is to solve with the "e_i"
> vectors, i=1,...,n where e_i = (0, ..., 0, 1, 0, ..., 0)^T with the "1" in
> the ith location.
>
> You could try to solve all RHS simultaneously by forming a MultiVector
> object with all e_i vectors, or you could "stripmine" by doing, say 10 RHS
> at a time.  Stripmining can make storage savings easier.
>
> I recommend the direct solvers in Amesos since your problem sizes are small.
> Amesos can solve multiple simultaneous RHS. You can also use the iterative
> methods in Belos, which can also solve multiple simultaneous RHS.
>
> I hope this helps.
>
> Mike
>
> On 8/31/10 1:20 PM, "Martin Vymazal" <martin.vymazal at vki.ac.be> wrote:
>
>> Hello Mike,
>>
>>   since it's a little testing code for the moment, I typically have
>> 1000 DOF (i.e. the full dense matrix would have 1000x1000 entries). I
>> don't think I'll play with meshes bigger than 5000 DOF. For the
>> moment, I'm just testing the concept.
>>
>>   Martin Vymazal
>>
>> Quoting "Heroux, Michael A" <maherou at sandia.gov>:
>>
>>> Martin,
>>>
>>> How big is your system, typically and at its largest?
>>>
>>> Mike
>>>
>>>
>>> On 8/31/10 1:03 PM, "Martin Vymazal" <martin.vymazal at vki.ac.be> wrote:
>>>
>>>> Hello Mark,
>>>>
>>>>   no, I'm not a physicist. My matrix is a discrete representation of
>>>> an operator acting between two finite element grids. Wherever I could,
>>>> I avoided the inversion by solving Ax=b. Unfortunately, now I really
>>>> need the complete inverse.
>>>>
>>>>    Best regards,
>>>>
>>>>   Martin Vymazal
>>>>
>>>> Quoting Mark Hoemmen <mhoemme at sandia.gov>:
>>>>
>>>>> On Aug 31, 2010, at 10:47 AM,
>>>>> trilinos-users-request at software.sandia.gov wrote:
>>>>>> Message: 1
>>>>>> Date: Tue, 31 Aug 2010 00:29:43 +0200
>>>>>> From: "Martin Vymazal" <martin.vymazal at vki.ac.be>
>>>>>> Subject: [Trilinos-Users] Inverse of a sparse matrix?
>>>>>> To: trilinos-users at software.sandia.gov
>>>>>> Message-ID: <20100831002943.122974kkn7rtlwif at horde.vki.ac.be>
>>>>>> Content-Type: text/plain; charset=iso-8859-1; DelSp=Yes; format=flowed
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>>  I'm sorry if this question was already answered somewhere, but I
>>>>>> searched and didn't find the answer. I'd like to ask what is the best
>>>>>> way to compute an inverse of a Epetra__FECrsMatrix. Thank you.
>>>>>
>>>>> Are you a physicist, and if so, do you wish to compute specific
>>>>> elements of the inverse?  If you are just solving linear systems
>>>>> Ax=b, you never want the inverse.  However, some physics
>>>>> applications do call for certain elements of the inverse.  If you
>>>>> only need, say, the diagonal entries of the inverse, there are less
>>>>> computationally expensive ways to do this than to compute the full
>>>>> inverse.
>>>>>
>>>>> mfh
>>>>> _______________________________________________
>>>>> Trilinos-Users mailing list
>>>>> Trilinos-Users at software.sandia.gov
>>>>> http://software.sandia.gov/mailman/listinfo/trilinos-users
>>>>>
>>>>>
>>>>
>>>>
>>>>
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>>>
>>
>>
>>
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>
>



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