[Nek5000-users] Adjacent vertices / cells

[nek5000-users at lists.mcs.anl.gov]

Hi Lee,

Just to be clear re. your original question - the (i,j,k,e) topology is point-based, not cell-based,
so one doesn't have a concept of 6 neighbors unless you are in the interior of a spectral element
or on the face of a spectral element.  At an edge or corner, you could have more or fewer than
6 neighbors.

If you instead define a cell (which would be defined, say, at the centroids of the N^3 cells within each element), you would have 6 neighbors unless you're on the boundary.

I would normally find these neighbors by invoking calls to setupds and dssum().  In one exchange, you could exchange your neighbors element number.  In a subsequent exchange you could exchange the cell index.   If you use gs_op() directly, I believe it supports integer arguments, rather than making the unseeingly an perhaps error-prone conversion to integers, though I've never had any difficulty call dssum directly and using reals.

It's important to use the gs_op (or equivalent drum) operations as that is the only viable/scalable approach in parallel. (Everything has been tested on anywhere from 1 to 6 million ranks).

I've done this several times before...and can probably dig up some code to give you cell based data,
assuming that's what you want.

Best,

Paul




________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Monday, May 08, 2017 7:38 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Adjacent vertices / cells


Hi Paul,


Thankyou very much for your prompt response,


I'm tracking an immersed object within the fluid. I can determine whether a velocity point is within the boundary using face normals and dot-products, but I need to know whether it is connected to an outside-boundary cell.


Cheers,


Lee

________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov <nek5000-users-bounces at lists.mcs.anl.gov> on behalf of nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
Sent: 08 May 2017 13:26:13
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Adjacent vertices / cells


Hi Lee,

The SEM is more function-based than cell based.

My guess is that Nek might alread support the higher-level
 operation you are trying to implement.  What is your
objective?

Best, Paul


________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Monday, May 08, 2017 6:52 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Adjacent vertices / cells


Hi all,


I'm just wondering if there's a way (given a particular velocity cell's local (i,j,k,e) co-ordinates within the domain) to access the 6 adjacent cells - even if they are located inside a different element.


If so, how does this deal with cells on the boundary, where there may exist fewer than 6 adjacent cells.


Many thanks,


Lee
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20170508/26275540/attachment-0001.html>