[ncl-talk] passing args within ncl scripts

[Rick Brownrigg]

Hi Jayant,

My apologies if I'm still not clear.  You say "It takes a lot of time to
read a variable and generate a plot."  Are you trying to read 24 files and
generate 24 plots? Or read 24 files and perform analysis and generate plots
from the composite?

It sounds like the latter -- are you trying to use subprocesses to read 24
files and end up with one array in memory composed from all 24 of them, so
that you can perform analysis and/or plots on that array?  Then no --
subprocesses won't do the job and NCL in general does not have a way to
perform concurrent reads into a shared memory space. The parent NCL script
executing other programs via the subprocess() function has no communication
with those programs.

The "addfiles" function is the NCL way of reading multiple files into a
common array; it is not concurrent to the best of my knowledge, but it does
the job.

Rick


On Tue, Jul 20, 2021 at 9:04 PM Jayant <jayantkp2979 at gmail.com> wrote:

> Thanks Rick,
> I want to use task parallelism. I have hourly files spanning a few months
> from a high resolution simulation. It takes a lot of time to read a
> variable and generate a plot. I have come across task parallelism (example
> 3) and want to modify the example such that I can use 24 processors to read
> 24 files at a time and save the desired variable in a parent array. And
> once the reading is complete, I can perform calculations (daily/monthly
> stats) on the parent array. I hope this helps understand what I intend to
> do.
> You mentioned a file based approach...and perhaps the example 3 does save
> individual plots and later combine frames. I wonder if it's good idea in my
> case????
> Best regards,
> Jayant
>
> On Tue, Jul 20, 2021 at 11:50 PM Rick Brownrigg <brownrig at ucar.edu> wrote:
>
>> Hi,
>>
>> If I understand you correctly, you are trying to get the second script to
>> update the array in the first script?  If so, that would not be possible,
>> as the two scripts execute as independent processes, operating in
>> independent memory spaces. They would need some other mechanism to
>> communicate results between each other, perhaps something like a file-based
>> approach.
>>
>> Perhaps explain in more detail what you are trying to do and why there
>> are two scripts involved, and others might be able to offer suggestions.
>>
>> Rick
>>
>>
>> On Tue, Jul 20, 2021 at 8:26 PM Jayant via ncl-talk <
>> ncl-talk at mailman.ucar.edu> wrote:
>>
>>> Hi,
>>> I want to call one ncl script (test_second.ncl) from within another ncl
>>> script (test_prime.ncl) using system command (in fact subprocess
>>> command). In doing so, I want to update an array (defined in
>>> test_prime.ncl) in the second call. I am getting zeros (unchanged!!). How
>>> to proceed? Is there something like global variables that can be defined?
>>> Below are the working example scripts:
>>> ;==================================================
>>> *test_prime.ncl*
>>> begin
>>>  ninp=10
>>>  inparr=new(ninp,float)
>>>  inparr=0.0
>>>
>>>  do i=0,ninp-1
>>>   command="ncl -Q test_second.ncl "+str_get_sq()+"ip="+i+str_get_sq()+"
>>> "+str_get_sq()+"tmparr="+inparr(i)+str_get_sq()
>>>   system(command)
>>>  end do
>>> print(inparr)
>>> end
>>> ;==================================================
>>> *test_second.ncl*
>>> begin
>>> tmparr=ip ; intend to perform some calculation and update
>>> end
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>>
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