[gradsusr] variables in .gs scripts

[Yi-Chih Huang]

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)<http://opengrads.org/doc/udxt/libbjt/libbjt.html#if_expr1_op_expr2_true_expr_false_expr_>
>
> In regular grads, a combination of maskout<http://grads.iges.org/grads/gadoc/gradfuncmaskout.html>
> ()/const() <http://grads.iges.org/grads/gadoc/gradfuncconst.html>functions can accomplish the same as the if() function above.
>
>    Arlindo
>
>
> --
> Arlindo da Silva
> dasilva at alum.mit.edu
>
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