[petsc-users] How to pass the parameters for KSP

[Barry Smith]

On Oct 6, 2010, at 9:26 PM, vedaprakash subramanian wrote:

> Can anyone tell me whether the concept I understood is correct or not.
> 
> If I am having a MATLAB function func(Matrix A, Vector x, Vector b, Matrix Q, Matrix M, int max_it, int tol, Vec* sol, int* err, int* iter, int* flag)   to be converted into a KSP solver, then I have to do these following steps.
> 
> 1. In KSPSetUp_func(KSP ksp), initialize  KSPDefaultGetWork(ksp,11);  // This tells the KSP that it is going to take 11 arguments
> 2. In KSPSolve_func(KSP ksp), declare 
>     Mat A, Q, M;
>     Vec x, b, *sol;
>     PetscInt max_it, *flag, *iter;
>     PetscScalar tol, *err;
> 
>     A  = ksp->work[0];
>     x   = ksp->work[1];
>     b   = ksp->work[2];
>     Q  = ksp->work[3];
>     M   = ksp->work[4];
>     max_it   = ksp->work[5];
>     tol  = ksp->work[6];
>     *sol   = ksp->work[7];
>     *err   = ksp->work[8];
>     *iter   = ksp->work[9];
>     *flag   = ksp->work[10];
> 
> ------------------------------
> Is the above said is correct. Is that the way to get the arguments of the KSPSolve.

  No this is very wrong. The KSPDefaultGetWork(ksp, just gets work vectors needed by the solver. It has nothing to do with number of arguments. 

> 
> Moreover, I have a doubt. What are these variables that are been used in cg.c
>   
>   stored_max_it = ksp->max_it;
>   X             = ksp->vec_sol;
>   B             = ksp->vec_rhs;
> 
> Where are these variables (ksp->max_it, ksp->vec_sol and ksp->vec_rhs) getting initialized.

  This is done in the various base KSP routines like KSPCreate() KSPSetTolerances(). The vec_sol and vec_rhs are set in the KSPSolve() routine.

   You are going to need to understand the workings of KSP for BCGS much better before tackling a new metthod.

   Barry

> 
> -Vedaprakash
> 
> On Wed, Oct 6, 2010 at 7:56 PM, vedaprakash subramanian <vedaprakashsubramanian at gmail.com> wrote:
> I need my KSP to take in Tolerence, flag, err, 3 matrices, right hand side vector. How can I make it to take all the parameters.
> 
> On Mon, Sep 20, 2010 at 11:00 AM, <petsc-users-request at mcs.anl.gov> wrote:
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>   1.  How to pass the parameters for KSP (vedaprakash subramanian)
>   2. Re:  How to pass the parameters for KSP (Barry Smith)
> 
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> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Sun, 19 Sep 2010 19:05:48 -0600
> From: vedaprakash subramanian <vedaprakashsubramanian at gmail.com>
> Subject: [petsc-users] How to pass the parameters for KSP
> To: petsc-users at mcs.anl.gov
> Message-ID:
>        <AANLkTinjiGMTMVB1yVx6JEvPhjGi_=T+QY6HK7wnHgOa at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> I am converting a MATLAB function into a KSP solver. I am doing it similar
> to BiCGStab. But I wanted to know how to pass the arguments of the function
> into KSP solver.
> 
> Thanks,
> Vedaprakash
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> ------------------------------
> 
> Message: 2
> Date: Sun, 19 Sep 2010 21:49:47 -0500
> From: Barry Smith <bsmith at mcs.anl.gov>
> Subject: Re: [petsc-users] How to pass the parameters for KSP
> To: PETSc users list <petsc-users at mcs.anl.gov>
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> 
> 
>  What arguments? Do you mean the right hand side x and the matrix? Or do you mean parameters like the relative tolerance in convergence?
> 
>  See src/ksp/ksp/examples/tutorials/ex1.c for a simple example.
> 
>   Barry
> 
> On Sep 19, 2010, at 8:05 PM, vedaprakash subramanian wrote:
> 
> > I am converting a MATLAB function into a KSP solver. I am doing it similar to BiCGStab. But I wanted to know how to pass the arguments of the function into KSP solver.
> >
> > Thanks,
> > Vedaprakash
> 
> 
> 
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