juggling with datafiles

[Charles Seman]

Chris,

If all of the defined variables are for the same physical domain, 
perhaps you could try swapping the variables in the time loop? Maybe 
something like this (warning: not tested, please check for errors):

n=1
open ctl.n * or whatever the name should be...
define var1 = var.1
close 1
n=n+1
while (n<=48)
open ctl.n
define var2 = var.1
define var2m1 = var2-var1
...
var1 = var2 * update var1 for next time
close 1
n=n+1
endwhile

I hope this helps,
Chuck

Chris Hayes wrote:
>
> Dear group,
>
> I loop through 48 subsequent files and create maps from them.
>
> Several of the weatherdata are cumulative, adding all precipitation 
> from the runtime to the hour of the prediction.
>
> I would like to show maps of precipitation in the time period. E.g. of 
> time #23 by subtracting val.#22 from val.#23.
>
> I need 2 files to be open at the same time to accomplish that.
>
> I am looking for a memory efficient way to open and close files, in a 
> loop for all files.
>
> This setup came to mind:
>
> Open 1
>
> Open 2
>
> Display 2-1
>
> Close 1
>
> Open 3
>
> Display 3-2
>
> Close 2
>
> Open 4
>
> Display 4-3
>
> But I am only allowed to close the most recently opened file.
>
> If I stop closing files I will end up having loads of files open:
>
> Open 1
>
> Open 2
>
> Display val.2- val.1
>
> Open 3
>
> Display val.3- val.2
>
> Open 4
>
> Display val.4- val.3
>
> (repeat until #48)
>
> Close 1-48
>
> when I’m at the 23^rd timestep I have file #1,#2 …. #23 open.
>
> I’m afraid the server will crash having so many files open.
>
> I just need #22 and #23 for that display moment.
>
> Or I have to close all files and re-open the last as # 1: file #22 
> becomes file 1 and file #23 becomes file 2:
>
> Open #22 (1)
>
> Open #23 (2)
>
> Display val.2- val.1
>
> Close #23 (2)
>
> Close #22 (1)
>
> Open #23
>
> Open #24
>
> Display val.2- val.1
>
> Close #24
>
> Close #23
>
> But closing a file (#23 in this case) to immediately open it again 
> seems inefficient.
>
> Is there a smart way to handle this?
>
> I was pondering:
>
> Open #1
>
> Open #2
>
> Display val.2- val.1
>
> Open #3 AS and REPLACING 1
>
> Display val.1- val.2 (effectively: #3-#2)
>
> Open #4 AS and REPLACING 2
>
> Display val.2- val.1 (effectively: #4-#3)
>
> Is that possible?
>
> FYI: I’m using a php script to send commands to opengrads, so I’m 
> quite flexible with the available loops.
>
> Thanks,
>
> Chris
>

-- 

Please note that Charles.Seman at noaa.gov should be considered my NOAA
email address, not cjs at gfdl.noaa.gov.

********************************************************************
 Charles Seman                                Charles.Seman at noaa.gov
 U.S. Department of Commerce / NOAA / OAR
 Geophysical Fluid Dynamics Laboratory         voice: (609) 452-6547
 201 Forrestal Road                              fax: (609) 987-5063
 Princeton, NJ  08540-6649            http://www.gfdl.noaa.gov/~cjs/
********************************************************************

"The contents of this message are mine personally and do not necessarily
reflect any position of the Government or NOAA."