[Gmsh] GhostElements Section

[Christophe Geuzaine]

> On 29 Aug 2018, at 02:00, Doug Shi-Dong <doug.shi-dong at mail.mcgill.ca> wrote:
> 
> Hello,
> 
> I am looking at the $GhostElements section of the MSH4 file format and there seems to be inconsistencies. According to the documentation:
> 
> <$GhostElements>
>   numGhostElement(int)
>   elementTag(int) partition(int) GhostCellOwner(int) GhostCellOwnerPartition(int) ...
> <$EndGhostElements>
> 
> 
> Here is my current understanding and what I would expect:
> 	• 'partition(int)' corresponds to the partition where the REAL cell is located
> 	• 'GhostCellOwner(int) corresponds to the number of partitions in which element #elementTag appears as a GHOST cell
> 	• 'GhostCellOwnerPartition(int)' corresponds to the list of partitions in which element #elementTag appears as a GHOST cell
> 
> However, when exporting the MSH4 format there seems to be a bug such that :
> 	• 'partition(int) corresponds to ONE of the partitions in which the element #elementTag appears as a GHOST cell
> 	• 'GhostCellOwnerPartition(int)' corresponds to the partition in which the REAL cell is located
> 
> As a result, if element #elementTag appears as a GHOST cell in multiple partitions, the current implementation will have the REAL cell partition number repeated multiple times in the 'GhostCellOwnerPartition(int)'.
> 
> Therefore, it seems that there has been a mix-up between 'partition' and 'GhostCellOwnerPartition'.
> 

Indeed: the documentation has been updated - see http://gmsh.info/dev/doc/texinfo/gmsh.html

Thanks for the feedback!

Christophe



> I am exporting a partitioned mesh in the MSH4 format using the latest stable binary (4.0.0, August 22 2018) and have tried the latest development build 296dd75f0b29090c28165df397cac4ff922832e5.
> 
> Thank you for time.
> 
> Best Regards,
> 
> Doug
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— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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