memory allocation

[li pan]

Dear Aron,
thanx for your answer. I've found the reason. As you
said, petsc need indexing information as well as the
dada. Furthermore, each node has 27 neighbours, since
I'm doing FEM calculation. I mistakened last time.

see u

pan


--- Aron Ahmadia <aja2111 at columbia.edu> wrote:

> Dear Pan,
> 
> I don't see everything going on here, but you have
> to account for
> around 1966080*(4 or 8) bytes + 1966080*21*(4 or 8)
> bytes of indexing
> information for storing the locations of the data in
> the Matrix, then
> if you're using doubles, 1966080*21*8 bytes of data
> information.
> Adding these up, I get something closer to 500 MB. 
> If PETSc is
> consuming more than 2 GB, there's probably something
> else going on to
> consume all that memory.  Are you using GMRES to
> solve the system?
> 
> Try calling as simple a version of your code as you
> can that sets up
> the mesh and pass in the -log flag on the command
> line and report back
> with the results.
> 
> ~A
> 
> 
> On 7/2/07, li pan <li76pan at yahoo.com> wrote:
> > Dear developers,
> > last week I asked a question about memory
> allocation.
> > I'm trying to comprehend it from another aspect.
> The
> > question is, if I have a mesh (HEX8) of size 128 x
> 128
> > x 40. There are three components for each node. In
> > case of displacement, it's (u,v,w). So there must
> be
> > 128 x 128 x 40 x 3 = 1966080 degrees of freedom.
> In
> > sparse pattern, each element must have 7 x 3 = 21
> > non-zeros, because each node has 6 neighbours,
> plus
> > itself, it's 7 nodes, then multiply 3 components,
> we
> > get 21. If everything is allright until now, we
> have
> > 1966080 x 21 non-zeros in the system matrix. This
> > corresponds 42 MB. I wonder why there was so much
> > memory required by petsc, more than 2 GB.
> > Probably, I'm wrong on some points. Please remind
> me.
> >
> > kind regards
> >
> > pan
> >
> >
> >
> >
> >      
>
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> 



       
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