[gradsusr] variables in .gs scripts

[Yaqiang Wang]

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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>



-- 
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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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