[Nek5000-users] Help With Basic NEK Configuration

[nek5000-users at lists.mcs.anl.gov]

Hi,

I am a new to NEK and I am trying to run a few examples for my OS scaling  
experiments. I went through the manual which is at:  
http://www.mcs.anl.gov/~fischer/new.pdf. In the chapter that speaks about  
a basic problem setup, there is a line in the 'Memory Requirements'  
section that says:

Total Memory Required for simulation = E(N +1)^3 points × 400(wds/pt) ×  
8bytes/wd

I have been playing around with the SIZE file a little bit and adjusting,  
lx1, lelt, lxd, lp and lelg parameters. However I am unable to find where  
I can adjust 'E' from the equation. I understand that 'lelt' is maximum  
elements per processor and 'lelg' is maximum elements per simulation? Is  
'lelg' same as 'E'? is 'lelt = lelg / nprocs' ? I assumed that 'E = lelg'  
and changed 'lelg' for 'timing' example to run it on a 4096 node  
configuration (1 rack of BG/P:Intrepid in VN mode). I keep getting the  
error:

Too many processors ( 4096 ) for to few elements ( 512 )

... and the value 512 does not seem to change although I have changed  
'lelg' and run 'makenek timing'. Is the value of 'E' picked up from the  
.re2 file? Would I have to generate it using 'genbox' after I change some  
other configuration?

I understand that NEK has been scaled upto 40 racks of Intrepid at  
Argonne. I am also trying to run experiments of upto 32 racks if possible.  
But I want to get started with smaller runs. Is there a repository of  
configurations or tarred files where I could get larger, successfully run  
problem instances?

Thanks.

Regards,
Harish Naik
Predoctoral Appointee
Mathematics & Computer Science Division
Argonne National Laboratory
P: (630) 252-2029
W: http://www.mcs.anl.gov/~hnaik