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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20070126/69a9e278/attachment.htm>
