if statement in grads

[Eric Altshuler]

John,

One problem I immediately see is that in your if statement:

'define aa=rain.2*24'
if (rainlow <= aa & aa < rainhigh)

you are trying to compare the script variables rainlow and rainhigh with 'aa', which is a GrADS defined data variable, not a script variable. This will not work. You need to assign a particular single value to the script variable aa. An example might be the following, with the dimension environment set to all dimensions fixed:

...
...
'set t 't1
...
'set z 'z1
...
'set x 'x1
'set y 'y1
'd 24*rain.2'
aa=subwrd(result,4)
if (rainlow <= aa & aa < rainhigh)
...
...

where x1, y1, z1 and t1 are the values (assigned to these script variables) you want for the fixed dimensions. You already have a looping structure set up for Z, and I assume you also have one for T, but you will also need to loop over the values of X and Y so that the script variable aa is assigned a single value in each iteration of the loop.

Best regards,

Eric L. Altshuler
Assistant Research Scientist
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
USA

E-mail: ela at cola.iges.org
Phone: (301) 902-1257
Fax: (301) 595-9793

----- Original Message -----
From: "John Guhin" <johnguhin at GMAIL.COM>
To: GRADSUSR at LIST.CINECA.IT
Sent: Thursday, March 12, 2009 12:31:00 PM GMT -05:00 US/Canada Eastern
Subject: Re: if statement in grads

Thanks Stephen. You are correct for more than one time step. But can we read
a 2D variable at all inside the if statement? Consider the following:

'open /raid/pray/processed_data/IWC/iwc.ctl'
'open /raid/pray/processed_data/AMSRE/rain-amsre_15jun06-31aug08.ctl'
rainlow=0 ; rainhigh=5;
lon1=0 ; lon2=360
lat1=-30 ; lat2=30
undef=-1e+34
z1=1
while(z1<19)
'set z 'z1
'define aa=rain.2*24'
if (rainlow <= aa & aa < rainhigh)
'd aave(iwc,lon='lon1',lon='lon2',lat='lat1',lat='lat2')'
else
'd aave(iwc*0+'undef',lon='lon1',lon='lon2',lat='lat1',lat='lat2')'
endif
z1=z1+1
endwhile

iwc is 3D. rain.2 is actually a 2D variable, so aa is  also 2D. I think
thats where the problem is.  Anybody has faced similar problem?
thanks.



On Thu, Mar 12, 2009 at 11:39 AM, Stephen R McMillan <
smcmillan at planalytics.com> wrote:

>
> John,
> The if statement you quoted--the one that Jennifer suggested--is valid, as
> is the nested method that Pablo suggested.  However, your unexpected results
> appear to indicate the "if..else" conditions (in particular are not changing
> during the second time loop iteration.  Since your variable 'aa' would be
> the same at each timestep, then I suppose 'iwc' may be the culprit. Have you
> tried echo-displaying the conditional results at each timestep to confirm
> their values?
> Stephen Mc
>
>
> *John Guhin <johnguhin at GMAIL.COM>*
> Sent by: GRADSUSR at LIST.CINECA.IT
>
> 03/11/2009 08:03 PM
> Please respond to
> GRADSUSR at LIST.CINECA.IT
>
> To
> GRADSUSR at LIST.CINECA.ITcc
> Subject
> Re: if statement in grads
>
>
>
>
> Thanks Stephen.
>  I simplified the script by considering only one time (t). The problem is
> indeed if statement.
> It seems if statement like this  if (rainlow <=aa & aa<rainhigh)
> does not work in grads. Is it true? or there is another way to solve my
> problem?
>
> thanks in advance.
>
>
> On Wed, Mar 11, 2009 at 5:07 PM, Stephen R McMillan <*
> smcmillan at planalytics.com* <smcmillan at planalytics.com>>wrote:
> John,
> Check the position of your "t1=1" line.  As it is, it would appear to
> repeat the 20 days once.  Did you intend to put "t1=1" before the outermost
> while loop?
> Stephen Mc
>
>
> *John Guhin <**johnguhin at GMAIL.COM* <johnguhin at GMAIL.COM>*>*
> Sent by: *GRADSUSR at LIST.CINECA.IT* <GRADSUSR at LIST.CINECA.IT>
>
> 03/11/2009 03:48 PM
> Please respond to
> *GRADSUSR at LIST.CINECA.IT* <GRADSUSR at LIST.CINECA.IT>
>
>
> To
> *GRADSUSR at LIST.CINECA.IT* <GRADSUSR at LIST.CINECA.IT>cc
> Subject
> Re: if statement in grads
>
>
>
>
>
>
> Hi,
>    I tried with
>  if (rainlow <=aa & aa<rainhigh)
>
>  but didn't work. Am I mising something?
>
> thanks in advance.
>
>
> On Wed, Mar 11, 2009 at 1:28 PM, Jennifer Adams <*jma at cola.iges.org*<jma at cola.iges.org>
> >wrote:
> Try  changing your if statement to:
> if (rainlow <=aa & aa<rainhigh)
> --Jennifer
>
> On Mar 11, 2009, at 1:19 PM, John Guhin wrote:
>
>
> Hi,
>     I am trying to use if statement in a grads script... which doesn't seem
> to work. I am
> attaching  the gs file. iwc is a 3D variable, and rain is 2D variable
> exactly in the same grids. I am trying to extract iwc when rain is within
> certain range. The script executes without any error, but the output repeats
> itself every 20 days. This means that the " if" statement is not working!!
> Any help would be appreciated.
>
>  'reinit'
> 'c'
> 'open iwc.ctl'
> 'open /rain.ctl'
> 'set gxout fwrite'
> 'set fwrite iwc_ppt_binned.dat'
>
> lon1=40 ; lon2=180
> lat1=-20 ; lat2=20
> undef=-1e+34
> rainlow=0 ; rainhigh=5;
>
> while(rainhigh<11)
> t1=1
> while(t1<21)
> 'set t 't1
> z1=1
> while(z1<19)
> 'set z 'z1
> 'define aa=24*rain.2(z=1)'
> if (rainlow <= aa < rainhigh)
> 'd aave(iwc,lon='lon1',lon='lon2',lat='lat1',lat='lat2')'
> else
> 'd aave(iwc*0+'undef',lon='lon1',lon='lon2',lat='lat1',lat='lat2')'
> endif
> z1=z1+1
> endwhile
> t1=t1+1
> endwhile
> rainlow=rainlow+5
> rainhigh=rainhigh+5
> endwhile
>
> 'close 2'
> 'close 1'
> 'disable fwrite'
>
> --
> John Guhin
> --
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705
> *jma at cola.iges.org* <jma at cola.iges.org>
>
>
>
>
>
>
>
> --
> John Guhin
>
>
>
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> --
> John Guhin
>
>
>
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> The information contained in this e-mail message is intended only for the
> use of the recipient(s) named above and may contain information that is
> privileged, confidential, and/or proprietary. If you are not the intended
> recipient, you may not review, copy or distribute this message. If you have
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--
John Guhin