[gradsusr] cdiff error

[Davide Sacchetti]

at least two problems:
1) cdiff cannot be performed against "lev" (you should use "z")
2) cdiff(lev,z) it's ok but you need z varying, otherwise it doesn't
work

Bye bye
Davide

Il giorno ven, 16/06/2017 alle 06.04 +0000, syairah atiqah atiq ha
scritto:
> Dear expert,
> 
> I'm trying to write the below formula into grads window using cdiff
> function and its error:
> 
> 
> Now we calculate dθ/dp  using center finite difference method in log
> pressure coordinate as follows. Note that we need zonal mean of
> dθ/dp  to calculate the vertical component of
>  EP flux and it does not matter whether we first calculate zonal mean
> of θ and the differentiate of differential first and then calculate
> zonal mean because the differentiation is 
> linear and the divisor p is same for all longitudes. So to avoid
> large computation it is advisable to first calculate zonal mean of
> theta and then do the following step for equation (2)
> 
> θp=dθ/dp = 1/p * dθ/d(log(p))
> = 1/p * (θ(n+1)-θ(n-1))/(logp(n+1)-lodp(n-
> 1))                                          (2)
> 
> In grads:
> ga-> 'define ptheta=cdiff(ttheta,lev)/cdiff(lev,lev)'
> Error from CDIFF:  Invalid dimension argument
>   2nd argument must be X, Y, Z, T or E
> Operation Error:  Error from cdiff function
>   Error ocurred at column 1
> DEFINE error:  Invalid expression.
> 
> I'm also try another way but still error:
> ga-> define ptheta=(cdiff(ttheta,z)/cdiff(lev,z))                    
>                                                  
>  Error from CDIFF:  Specified dimension non varying                  
>                                                   
>  Operation Error:  Error from cdiff function                        
>                                                     
>  Error ocurred at column 2                                          
>                                                  
>  DEFINE error:  Invalid expression.        
> 
> 
> Anyone can help me?
> 
> Thank you and really appreciate it
> 
> Regards,
> Atiqah
> Postgraduate University Malaya,
> Malaysia
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