extracting work vectors

[Jed Brown]

On Fri, 04 Dec 2009 12:51:27 +0100, jarunan at ascomp.ch wrote:
> 
> Hi Jed,
> 
> Thanks for the advice. I took a look in PCShellSetApplyRicharson() and  
> its apply function.
> 
> PetscErrorCode apply (PC pc,Vec b,Vec x,Vec r,PetscReal rtol,PetscReal  
> abstol,PetscReal dtol,PetscInt maxits)
> 
> b - right-hand-side
> x - current iterate
> r - work space
> 
> 1. Can I use PCShellSetApplyRicharson() with KSPGMRES? or it is  
> restrict only for Richardson solver.

Richardson only.

> 2. Is x equivalent to xin in PCShellSetApply(pc,apply(PC pc,Vec  
> xin,Vec xout))?

No, preconditioning Richardson is a different beast entirely.

> 3. Are b vector is the right hand side specified by user and r the  
> work vector in the iterations?

Yes, r is just work space, you are not required to use it.

It's unlikely that you actually want to use Richardson, you should write
apply(PC,Vec,Vec).

Jed