[MITgcm-support] Coding help: random numerical errors while running in MPI

[Christopher L. Wolfe]

Hi all,

I'm trying to write a package for the MITgcm that does zonal averages  
along isopycnals. I've managed to get it working on in a single tile  
configuration, but when I try to run it using multiple tiles using  
MPI, I occasionally (about 1 in 5 runs) get random errors in the  
output. These errors are on the order of 10% of the correct output  
values and they only seem to infest a few (randomly varying) grid  
points at a time. I mainly figured out how to do inter-tile  
communication by copying other routines in the MITgcm, so I may have  
made a mistake that would be obvious to someone more experienced with  
MPI. I was hoping someone might be able to help me find the problem.

The only piece that makes explicit use of MPI is the output routine,  
which makes use of a modified version of gather_xy. (The averaged  
data don't fit onto the computational grid, so I couldn't figure out  
how to write the data with the standard IO routines.) These files are  
attached.

The weird thing is that when the commented out write statement on  
lines 65--67 uncommented, the code works fine.

Thanks in advance for the help,
Christopher

-------------- next part --------------
A non-text attachment was scrubbed...
Name: isoave_output.F
Type: application/octet-stream
Size: 2995 bytes
Desc: not available
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20080604/0b04667a/attachment.obj>
-------------- next part --------------


-------------- next part --------------
A non-text attachment was scrubbed...
Name: isoave_gather.F
Type: application/octet-stream
Size: 3587 bytes
Desc: not available
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20080604/0b04667a/attachment-0001.obj>
-------------- next part --------------


-----------------------------------------------------------
Dr. Christopher L. Wolfe                   858-534-4560
Physical Oceanography Research Division    OAR 357
Scripps Institution of Oceanography, UCSD  clwolfe at ucsd.edu
-----------------------------------------------------------