[MITgcm-support] AIX and numerical diffusion

[Haferman, Jeffrey (Jeff) (CIV)]

I recently copied an MITgcm model that has been running fine compiled
under FC3 Linux with 4 dual core AMD 865 processors (i.e. 8 processing
elements total) to an IBM p690 running AIX 5.2 (power 4 chip), also
using 8 processors.  For the IBM I used a modified version of the
build_options file called "sp4+mpi" supplied with MITgcm, and things
compiled just dandy.  

 

I guess I should probably go back and run some of the test cases
supplied with MITgcm, but, what I am seeing with my model is that I have
pretty good agreement with the model output (T, S, u,v,w) between the
Linux and IBM runs for the first couple of hundred time steps, though I
see differences in some of the least significant digits.  After a few
hundred timesteps, the model "blows up" numerically on the IBM, but
converges fine on the Linux machine.  I am using identical input for
both cases.

 

I guess I can try to decrease the timestep on the IBM to see if it
helps, but does has anyone else had this type of experience when moving
a model to a new platform, and can you offer some suggestions?  I am
using the IBM xlf and xlc compilers under their POE environment, if that
makes any difference.

 

Jeff

 

 

 

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