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

[Franck Houssen]

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). 

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

Franck 

----- Mail original -----

> 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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