Hi all,
> It's looking like there could be a decent amount of hacking in the ExodusII
> code to get the writer to work properly for this (as well as the reader to
> read it back in without issues). The main issue appears to be that NetCDF
> doesn't allow creating a dimension of 0 length/size. Thus the stuff in
> VTK/ThirdParty/exodusII/vtkexodusII would need to be changed.
>
> Both the reader and writer make the assumption that if the num_nodes
> dimension exists that there are points to be read in.
Yes, that is a basic assumption of the Exodus file format: each rank is
assigned a subset of the cells and nodes in the simulation domain, since
otherwise there is no state to store. If rank 0 of a simulation has no nodes
(and thus cannot have cells either), then it should probably not participate in
writing the Exodus dataset. You could create an MPI subcontroller without the
rank 0 process and have the writer use that.
> At this point I'm thinking it's better to modify the reader than the writer...
I would be very wary of this.
David
>
> On Fri, Jan 13, 2017 at 2:59 PM, Andy Bauer <[email protected]> wrote:
> Hi Ken,
>
> Thanks for the input.
>
> There is an explicit check in the writer to see if there are any points
> before writing out point data. I took that check out and am hitting a NetCDF
> error that the "num_nodes" dimension isn't specified. It will probably take a
> bit of investigating to fix this but at least you've helped me go down the
> correct path.
>
> Thanks,
> Andy
>
> On Fri, Jan 13, 2017 at 2:44 PM, Moreland, Kenneth <[email protected]> wrote:
> Andy,
>
>
>
> That sounds like a bug in our Exodus writer to me. I’m not positive, but I’m
> pretty sure that you can specify in Exodus point and cell arrays if no grid
> points or cells exist. The writer is probably making a shortcut and skipping
> that if there is no actual data.
>
>
>
> -Ken
>
>
>
> From: ParaView [mailto:[email protected]] On Behalf Of Andy Bauer
> Sent: Friday, January 13, 2017 12:00 PM
> To: [email protected]
> Subject: [EXTERNAL] [Paraview] exodusII reader & writer in parallel
>
>
>
> Hi,
>
> I'm trying out the ExodusII writer in parallel and had some questions about
> how it should work in general when there isn't any data on process 0.
> Currently what happens in ParaView is that a file for each process is written
> out but the file corresponding to process 0 doesn't have any grid information
> or field data (an example is attached). When I read this back into ParaView
> using the built-in server (i.e. in serial) the ExodusII reader gets the
> proper points and cells but no field data is read in.
>
> So my question is this, does the ExodusII file format allow specifying point
> and cell arrays in a file if no grid points or cells exist?
>
> I'm tempted to fix this issue by modifying the reader to properly pass the
> field data information to process 0 from another one that has data but wanted
> to get the community's thoughts on this before I go through the
> implementation. The alternative would be to modify the writer to include
> point and cell data information and that's probably a better solution,
> assuming that the ExodusII format allows for that.
>
> Thanks,
>
> Andy
>
> ps. Attached is a sample set of ExodusII files that doesn't have any data on
> parallel.ex2.4.0 in case someone wants to play around with it.
>
>
>
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