[pooma-dev] FW: Questions about data in Fields

[William Nystrom]

Hi Scott,

 

Thanks for your reply.  I am trying to interface to a linear solver 
package that is written

in f77.  This is a package that I have used alot in the past and am 
very familiar with.  I

talked with you 2-3 years ago about the interface to this package with the 
idea of trying

to interface to Pooma 1.  But I never really had time to pursue that 
work.  Now I am

trying to interface to this package using Pooma 2.  I talked with Jim 
about this when John

and I came down to Proximation a couple of months ago.  I don't know 
if I can describe

the interface well enough for you to follow it or for that matter, even if 
it is worthwhile

at this stage.  My ultimate goal is to be able to call this package 
with the minimum amount

of data copying but right now, John and I have compromised on doing some 
extra copying.

Fundamentally, what I need to pass to this fortran linear solver package is 
the address of

the beginning of the chunk of data on a processor.  The data must be 
contiguous.  So, this

means that the data cannot have any guard cells.  Also, I would 
presume that it means that

I can only have 1 vnode or patch per processor.  We were wanting to 
use Pooma 2 Fields

for all this work.  All of our current physics code uses Pooma 2 
Fields.  So there was a

desire to be able to use Pooma 2 Fields for this work as well rather than 
having to use

arrays.

 

I don't know if this is really answering any of your questions but I have 
to go for now.

I'll give this some more thought and perhaps respond some more to your 
email.

 

Thanks,

 

Dave


----- Original Message ----- 

From: Scott 
Haney  

To: sunsetmesa at earthlink.net 
Cc: pooma-dev at pooma.codesourcery.com 

Sent: 7/25/2001 7:51:15 AM 

Subject: Re: [pooma-dev] FW: Questions 
about data in Fields





Hi Dave,

 

The data in fields is not necessarily continuous. We allocate based on a 


vertex-centered domain for all subfields. This is done so that when the 


field is partitioned, all of the subfields will be aligned. This fixes 


the nasty problems we had in R1 with slightly different sized fields 

giving dramatically different partitionings. This improves robustness 


and should improve performance. Note as well that if you are looking at 


a patch and there are internal guard layers, the data won't be 

continuous either.

 

Your best bet is to assign the patch data to a brick-array of the 

correct size. This will make the data continuous. However, it would be 


helpful to see a snippet showing exactly what you're trying to do. This 


would also help with respect to the size question - I am surprised by 


the behavior you're reporting.

 

Scott

 

On Tuesday, July 24, 2001, at 01:24 PM, William Nystrom wrote:

 

  Hi Guys,

   

  I talked to Jim about interfacing to some fortran linear solver code 


  awhile back and then before I left for

  vacation, John and I did some work to try and write the interface for 


  our application using Pooma 2 so

  we could use this fortran linear solver package.  One of the 
things I 

  am trying to do is to query a Pooma 2

  Field and find out the size of the data that is local to a 
processor.  

  I've done this query for the domain object

  for a Field and for a cell centered field, it reports sizes in each 


  dimension or coordinate that are one more

  than they should be.  John told me that you guys had decided to 


  allocate enough space for a vertex centered

  field even if the field was cell centered - as an optimization of some 


  sort.  I am worried that the data for a

  cell centered field may not be contiguous because of the extra padding 


  that occurs for cell centered fields

  and because the domain object thinks it's size in each dimension is 
one 

  larger.  Can you tell me if the data

  for a cell centered field that is local to a processor with one patch 


  per processor is actually contiguous in

  memory?  I can test this experimentally but I have not had a 
chance to 

  do this yet.  Also, can you tell me the

  recommended way to get the correct size of my data on a local 
processor 

  for a cell centered Pooma 2

  Field?

   

  Please send replies to sunsetmesa at earthlink.net  as I am not 
able right 

  now to read my lanl email and I

  am not subscribing to pooma-dev from my ISP account.

 

 

 




 

--- William Nystrom

--- sunsetmesa at earthlink.net 

--- EarthLink: It's your Internet.
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