Re: DA question

[Barry Smith <bsmith@xxxxxxxxxxx>]

On Apr 29, 2008, at 2:27 PM, Amit.Itagi@xxxxxxxxxxx wrote:

> Barry,
>
> Can this be achieved using SDA ? I am working with regular arrays, and
> doing only explicit updates.

   Yes. SDA actually uses the DA, it just hides the Vec concept from  
the user.

   Barry

> Thanks
>
> Rgds,
> Amit
>
> owner-petsc-users@xxxxxxxxxxx wrote on 04/29/2008 01:28:17 PM:
>
> >   If you are running a true explicit scheme then you have no need
> > to ever have a "global representation" at each time step. In this
> > case you can use DALocalToLocalBegin() then DALocalToLocalEnd()
> > and pass the same vector in both locations. This will update the  
> > ghost
> > points but WILL NOT do any copy of the local data since it is already
> > in the correct locations.
> >
> >   Barry
> >
> > On Apr 29, 2008, at 8:54 AM, Amit.Itagi@xxxxxxxxxxx wrote:
> >
> > > Hi,
> > >
> > > I spent some more time understanding DA's, and how DA's should serve
> > > my
> > > purpose. Since in the time domain calculation, I will have to
> > > scatter from
> > > the global vector to the local vector and vice-versa at every
> > > iteration
> > > step, I have some follow-up questions.
> > >
> > > 1) Does the scattering involve copying the part stored on the local
> > > node as
> > > well (i.e. part of the local vector other than the ghost values), or
> > > is the
> > > local part just accessed by reference ? In the first scenario, this
> > > would
> > > involve allocating twice the storage for the local part. Also, does
> > > the
> > > scattering of the local part give a big hit in terms of CPU time ?
> > >
> > > 2) In the manual, it says "In most cases, several different vectors
> > > can
> > > share the same communication information (or, in other words, can
> > > share a
> > > given DA)" and "PETSc currently provides no container for multiple
> > > arrays
> > > sharing the same distributed array communication; note, however,
> > > that the
> > > dof parameter handles many cases of interest". I am a bit confused.
> > > Suppose
> > > I have two arrays having the same layout on the regular grid, can I
> > > store
> > > the first array data on one vector, and the second array data on the
> > > second
> > > vector (and have a DA with dof=1, instead of a DA with dof=2), and
> > > be able
> > > to scatter and update the first vector without scattering/updating  
> > > the
> > > second vector ?
> > >
> > > Thanks
> > >
> > > Rgds,
> > > Amit
> > >
> > > owner-petsc-users@xxxxxxxxxxx wrote on 04/09/2008 04:09:59 PM:
> > >
> > > > Hi Amit,
> > > >
> > > > Why do you need two staggered grids? I do EM finite difference
> > > > frequency
> > > > domain modeling on a staggered grid using just one DA. Works
> > > > perfectly
> > > fine.
> > > > There are some grid points that are not used, but you just set them
> > > > to
> > > zero
> > > > and put a 1 on the diagonal of the coefficient matrix.
> > > >
> > > >
> > > > Randy
> > > >
> > > >
> > > > Amit.Itagi@xxxxxxxxxxx wrote:
> > > > > Hi Berend,
> > > > >
> > > > > A detailed explanation of the finite difference scheme is given
> > > > > here :
> > > > >
> > > > > http://en.wikipedia.org/wiki/Finite-difference_time-domain_method
> > > > >
> > > > >
> > > > > Thanks
> > > > >
> > > > > Rgds,
> > > > > Amit
> > >
> > > > >           Berend van Wachem
> > >
> > > > >           <berend@chalmers.
> > >
> > > > >           se>
> > > To
> > > > >           Sent by:                  petsc-users@xxxxxxxxxxx
> > >
> > > > >           owner-petsc-users
> > > cc
> > > > >           @mcs.anl.gov
> > >
> > > > >           No Phone Info
> > > Subject
> > > > >           Available                 Re: DA question
> > >
> > > > >
> > >
> > > > >
> > >
> > > > >           04/09/2008 02:59
> > >
> > > > >           PM
> > >
> > > > >
> > >
> > > > >
> > >
> > > > >           Please respond to
> > >
> > > > >           petsc-users@xxxxx
> > >
> > > > >                nl.gov
> > >
> > > > >
> > >
> > > > >
> > >
> > > > > Dear Amit,
> > > > >
> > > > > Could you explain how the two grids are attached?
> > > > > I am using multiple DA's for multiple structured grids glued
> > > > > together.
> > > > > I've done the gluing with setting up various IS objects. From the
> > > > > multiple DA's, one global variable vector is formed. Is that what
> > > > > you
> > > > > are looking for?
> > > > >
> > > > > Best regards,
> > > > >
> > > > > Berend.
> > > > >
> > > > >
> > > > > Amit.Itagi@xxxxxxxxxxx wrote:
> > > > > > Hi,
> > > > > >
> > > > > > Is it possible to use DA to perform finite differences on two
> > > staggered
> > > > > > regular grids (as in the electromagnetic finite difference time
> > > > > > domain
> > > > > > method) ? Surrounding nodes from one grid are used to update the
> > > > > > value
> > > in
> > > > > > the dual grid. In addition, local manipulations need to be done
> > > > > > on the
> > > > > > nodal values.
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > Rgds,
> > > > > > Amit