[petsc-dev] How to get L and D from cholesky factorisation ?

[Hong]

Franck:

> OK. I 'll try to shed some light on this when I have a MUMPS's guy around
> !... And try to ask to get that exposed if possible (?).
> I guess the answer is the same for getting L and U from LU factorisation
> (using MUMPS).
>

Why do you want to see L and U?

>
> What about the same question when using any other package ? (say SUPERLU)
>

Would Same response, same response from PETSc as well. Logical L and U are
actually stored in strange data structures for efficient data accessing
(see our paper attached),  which are not intended to be exposed to users.

Hong

>
> ------------------------------
>
> *De: *"Hong" <hzhang at mcs.anl.gov>
> *À: *"Franck Houssen" <franck.houssen at inria.fr>
> *Cc: *"For users of the development version of PETSc" <
> petsc-dev at mcs.anl.gov>
> *Envoyé: *Jeudi 24 Août 2017 17:00:40
> *Objet: *Re: [petsc-dev] How to get L and D from cholesky factorisation ?
>
>
> mumps stores  LDLt using its private internal data structure, which is
> not exposed to user and can be used only via mumps API.
> Either ask mumps developer about it or use a debugger to step into mumps
> source code.
>
> Hong
>
> On Thu, Aug 24, 2017 at 9:46 AM, Franck Houssen <franck.houssen at inria.fr>
> wrote:
>
>> How to get L (as a Mat) and D (probably as a Vec) from cholesky
>> factorisation ?
>>
>> I googled and looked in the doc but didn't find any obvious answer. I am
>> not sure to get the steps to follow: is there a dedicated example ?
>>
>> To make it short, I have:
>> PCSetType(pc, PCCHOLESKY); // LDLt
>> PCFactorSetMatSolverPackage(pc, "mumps");
>> PCFactorGetMatrix(pc, &f);
>> MatGetInertia(f, ....); // OK !
>>
>> Now, I would like to get/see L and D: how to get them ?
>>
>> From petsc/src/ksp/ksp/examples/tutorials/ex52.c, I would say
>> MatGetDiagonal(f, D) returns D: correct ? If so, how to get L as well ?
>>
>> A related question would be : how to get L and U from a PCLU
>> factorisation ?
>>
>> Franck
>>
>
>
>
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