Using PETSc in structured c-grid for CFD and multigrid

[Berend van Wachem]

Hi Ben,

Sure you can - it just means you will need to save the X,Y,Z locations 
of the grid points as well. All a DA requires is a regular I,J,K 
numbering over your grid.

Berend.

> Hi,
>
> just to clarify. I'm using structured grid but not cartesian ie
> strictly horizontal/vertical. So I can't DA, can I?
>
> But can I use DMMG? So PETSc comes with a multigrid preconditioner
> and solver?
>
> Thank you
>
> On 1/26/07, Matthew Knepley <knepley at gmail.com> wrote:
> > On 1/25/07, Ben Tay <zonexo at gmail.com> wrote:
> > > Hi,
> > >
> > > I was discussing with another user in another forum
> > > (cfd-online.com) about using PETSc in my cfd code. I am now
> > > using KSP to solve my momentum and poisson eqn by inserting
> > > values into the matrix. I was told that using PETSc this way is
> > > only for unstructured grids. It is very inefficient and much
> > > slower if I'm using it for my structured grid because I am not
> > > exploiting the regular structure of my grid.
> > >
> > > Is that true? I'm solving flow around airfoil using c-grid.
> >
> > If you are using a Cartesian grid, the  DA  formulation is better.
> > However, this nonsense from people about
> > "massive  inefficiency"  is just crap. There is a small difference
> > in time which is almost trivial. However, there
> > is a big difference in ease of programming. I am always fascinated
> > how people can magnify small problems
> > in order to preserve their job.
> >
> >
> >  So how can I improve? Is it by using DA? I took a glance and it
> > seems
> >
> > > quite complicated.
> >
> > Wrong glance. Much simpler.
> >
> >
> >  Also, is multigrid available in PETSc? Chapter 7 discusses about
> > it but
> >
> > > it seems very brief. Is there a more elaborate tutorial besides
> > > that c examples?
> >
> > Yes, use DMMG. Much easier with DA.
> >
> >   Matt
> >
> >
> >  Hope someone can give me some ideas.
> >
> > > Thank you.
> >
> > --
> > One trouble is that despite this system, anyone who reads journals
> > widely and critically is forced to realize that there are scarcely
> > any bars to eventual
> > publication. There seems to be no study too fragmented, no
> > hypothesis too trivial, no literature citation too biased or too
> > egotistical, no design too
> > warped, no methodology too bungled, no presentation of results too
> > inaccurate, too obscure, and too contradictory, no analysis too
> > self-serving,
> > no argument too circular, no conclusions too trifling or too
> > unjustified, and
> > no grammar and syntax too offensive for a paper to end up in
> > print. -- Drummond Rennie