[gradsusr] variables in .gs scripts

[Yaqiang Wang]

1. maskout the rh values less than 100 to missing: rh=maskout(rh,rh-100)
2. get a new rh with the negtive values which are larger than 100
before (100 is now 0): rh=100-rh
3. maskout the negtive values: rh=maskout(rh,rh)
4. get mai values: mai=elr-malr
5. maskout mai: mai=maskout(mai,rh)
6. const mai missing values to 0: mai=const(mai,0,-u)

On Tue, Nov 15, 2011 at 10:58 AM, Yi-Chih Huang <dscpln at gmail.com> wrote:
> Hello,
>
>     I had read the documents about const and maskout online.  However,
> probably my understanding about const and maskout is so shallow that I can't
> use a combination of const and maskout to accomplish the function of the if
> statement.  Thus, I posed the question.
>
>     Thanks,
>
>                    Yi-Chih
>
>
> On Mon, Nov 14, 2011 at 9:41 PM, Yaqiang Wang <yaqiang.wang at gmail.com>
> wrote:
>>
>> You can find the usage of const and maskout from online help document.
>> http://www.iges.org/grads/gadoc/gradfuncconst.html
>> http://www.iges.org/grads/gadoc/gradfuncmaskout.html
>>
>> On Tue, Nov 15, 2011 at 10:28 AM, Yi-Chih Huang <dscpln at gmail.com> wrote:
>> > Hello,
>> >
>> >     I work on regular grads.  I have searched online for the examples to
>> > use
>> > const and maskout instead of if statement.  But I can't find any
>> > example.
>> > Could anyone show me an example to use const and maskout instead of if
>> > statement?
>> >
>> >     Thanks much for your help,
>> >
>> >                    Yi-Chih
>> >
>> >
>> > On Mon, Nov 14, 2011 at 4:25 PM, Arlindo da Silva <dasilva at alum.mit.edu>
>> > wrote:
>> >>
>> >> On Mon, Nov 14, 2011 at 3:40 PM, Yi-Chih Huang <dscpln at gmail.com>
>> >> wrote:
>> >>>
>> >>> Hello,
>> >>>
>> >>>     I want to calculate variable 2 based on the value of some variable
>> >>> as
>> >>> follows.
>> >>>
>> >>> When var1 = 100, then  var2 =  (calculation 1)
>> >>> When var1 != 100, then  var2 = (calculation 2)
>> >>>
>> >>> I wrote a .gs script as follows.  But the condition rh=100 did not
>> >>> effect.  Could anyone reveal what would be the right command in .gs
>> >>> script
>> >>> to give the condition in which variables are in the .ctl file?
>> >>>
>> >>>
>> >>>
>> >>> "malr=dalr*(1+2500000*q/287/tk)/(1+0.622*pow(2500000,2)*q/1004/287/tk/tk)"
>> >>> "elr=-(tk(z+1)-tk(z-1))/(height(z+1)-height(z-1))"
>> >>>
>> >>> if (rh=100) then
>> >>>    "mai=elr-malr"
>> >>> else
>> >>>    "mai=0"
>> >>> endif
>> >>
>> >> GrADS expression parser and the scripting language do not share the
>> >> same
>> >> name space. Therefore you cannot have an if statement as above where
>> >> you
>> >> reference a gridded variable.  If you are using opengrads, the if()
>> >> function
>> >> could accomplish what you want:
>> >> 'mai = if(rh,=,0,elr-malr,0)'
>> >> For more information on if() see:
>> >> if(EXPR1,OP,EXPR2,TRUE_EXPR,FALSE_EXPR)
>> >> In regular grads, a combination of maskout()/const() functions can
>> >> accomplish the same as the if() function above.
>> >>    Arlindo
>> >>
>> >> --
>> >> Arlindo da Silva
>> >> dasilva at alum.mit.edu
>> >>
>> >> _______________________________________________
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>> >>
>> >
>> >
>> > _______________________________________________
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>> >
>> >
>>
>>
>>
>> --
>> *************************************************
>> Dr. Yaqiang Wang
>> Chinese Academy of Meteorological Sciences (CAMS)
>> 46, Zhong-Guan-Cun South Avenue
>> Beijing, 100081
>> China
>>
>> yaqiang.wang at gmail.com
>>
>> http://www.meteothinker.com
>> **************************************************
>>
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>
>
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-- 
*************************************************
Dr. Yaqiang Wang
Chinese Academy of Meteorological Sciences (CAMS)
46, Zhong-Guan-Cun South Avenue
Beijing, 100081
China

yaqiang.wang at gmail.com

http://www.meteothinker.com
**************************************************