if statement in grads

Thu Mar 12 17:05:23 EDT 2009

 Thanks Eric. It worked out perfectly. One remaining problem is : I don't
want to write rain.2 in the file that I am creating.  Because of 'd
24*rain.2' it is also written in the output file. Is there any way to
suppress rain.2, and write only the intended variable (iwc)?
thanks again.

On Thu, Mar 12, 2009 at 3:48 PM, Eric Altshuler <ela at cola.iges.org> wrote:

> 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
> >
> >
> >
> > ***************************************************
> > 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
> > received this communication in error, please notify the sender
> immediately
> > by e-mail, and delete the original message.
> > ***************************************************
> >
>
>
>
> --
> John Guhin
>

--
John Guhin
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