Re: [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: address@hidden

Cc: address@hidden

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 address@hidden 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

--- address@hidden

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