[gradsusr] Slow performance using 'sum'

[Dan Leins]

All,

I have a GrADS script I use, among other things, to calculate run total
precip over my model domain throughout my model run (output format is
grib2). I create images of numerous fields on an hourly basis (say 72hrs
worth for example), so I produce 72 runtotal precip images. As the script
runs and iterates through a loop, my code to calculate the runtotal looks
like this:

'define runtotal=sum(apcpsfc.1, t=2, t='dis_t')'
'display runtotal'

where dis_t is the hour I am currently working on.

My script works fine and fast early on, but slows down over time.
Naturally, I assume the amount of time it takes to 'sum' hours of precip
will increase as I get further into my run. However, if I kill and restart
my script at an arbitrary time (dis_t=60) for example, this calculation
speeds right back up again.   Likewise if I comment out this portion of my
script, the rest of my script moves along at the same pace the entire time.
I'm thinking some resources aren't being released properly while the script
is running since the problem seems to go away if I kill/restart my script.

Is there a more efficient way to calculate a runtotal than the method shown
above?  I've been careful to undefine any variables after each iteration of
my loop so I don't think that's a factor.

Any help would be great!
Thanks,
Dan Leins
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