[Trilinos-Users] [EXTERNAL] PHG_EDGE_SIZE_THRESHOLD is low

Vishal Boddu vishal.boddu at fau.de
Wed Jan 10 06:08:07 EST 2018


Thank you Karen for your detailed answer.

We have chosen to raise PHG_EDGE_SIZE_THRESHOLD value to suppress the 
warning. The discussed example was indeed a test case.


On 01/09/2018 06:15 PM, Devine, Karen D wrote:
> The PHG partitioner is a hypergraph partitioner that can be used for graph partitioning.
> Before partitioning, it removes dense edges that contain more than
> PHG_EDGE_SIZE_THRESHOLD * total_number_of_vertices
> vertices, as these edges likely will incur high communication costs regardless of the partition.
>
> Your example is an extreme case.   You are doing graph partitioning (with number of vertices per edge always equal to 2) of a problem with total_number_of_vertices = 2.  Thus, the only edge has all the vertices and is, thus, dense.  There is no balanced partition that can avoid communication across that edge.  So we remove the edge.
>
> I assume this test problem is not a real use case.  If you try a problem with nine elements, you should not see this warning.  Or you can set PHG_EDGE_SIZE_THRESHOLD to 1.0.
>
> The Zoltan user guide has info on Zoltan parameters.  For this issue, see http://www.cs.sandia.gov/zoltan/ug_html/ug_alg_phg.html
> ________________________________________
> From: Trilinos-Users <trilinos-users-bounces at trilinos.org> on behalf of Vishal Boddu <vishal.boddu at fau.de>
> Sent: Tuesday, January 9, 2018 6:50 AM
> To: trilinos-users at trilinos.org
> Cc: Denis Davydov
> Subject: [EXTERNAL] [Trilinos-Users] PHG_EDGE_SIZE_THRESHOLD is low
>
> Dear all,
>
> We are using Zoltan (Trilinos 12.12.1) to partition a graph and I don't
> quite understand the following warning produced:
>
> WARNING: PHG_EDGE_SIZE_THRESHOLD is low (0.250000), resulting in only 0
> edges
> remaining.
>
> These were thrown when I tried to partition a graph (two quadrilaterals
> sharing an edge) with two MPI processes. The only place which prints
> such warnings is:
> https://github.com/trilinos/Trilinos/blob/f0350316239aaf41e8e6b82378612aaedf9cc72c/packages/zoltan/src/phg/phg_build.c#L1776
>
> I appreciate any help with figuring out what this means and if this
> warning is important or it could be ignored?
>
> Kind regards,
>
>
> Vishal Boddu M.Sc.(hons.)
> Chair of Applied Mechanics
> University of Erlangen-Nuremberg
> Paul-Gordan-Straße 3, 91058 Erlangen
> Tel: + 49-9131-85-64410, Fax: + 49-9131-85-28503
> vishal.boddu at fau.de | www.ltm.tf.fau.de
>
> _______________________________________________
> Trilinos-Users mailing list
> Trilinos-Users at trilinos.org
> https://trilinos.org/mailman/listinfo/trilinos-users

Kind regards,


Vishal Boddu M.Sc.(hons.)
Chair of Applied Mechanics
University of Erlangen-Nuremberg
Paul-Gordan-Straße 3, 91058 Erlangen
Tel: + 49-9131-85-64410, Fax: + 49-9131-85-28503
vishal.boddu at fau.de | www.ltm.tf.fau.de



More information about the Trilinos-Users mailing list