[ncl-talk] SPEI (drought index) calculation...

[Dennis Shea]

NCL's *cdfgam_p
<https://www.ncl.ucar.edu/Document/Functions/Built-in/cdfgam_p.shtml>
*documentation
mentions 'gamma' functions from R, Matlab and Excel.

What is your 'gmm_transform' supposed to return?









On Thu, Apr 17, 2025 at 2:32 AM qudsia zafar via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hi i am using cru datasets (ts 4.08) for precipitation and potential
> evapotranspiration. I have done (precip_minus_pet = prc - pet) and then
> I have used the function 'dim_gamfit_n' to estimate shape and scale
> parameters for the gamma distribution fitting.
>
> However in the next step of spei calculation I need to do the following:
>
> spei = gmm_transform(precip_minus_pet, shape, scale)
>
> I have now all the three data (precip_minus_pet, shape, scale) but i
> don't know if NCL has a gamma transformation function available? I have
> seen 'cdfgam_p' but I don't know if this corresponds to the gamma
> transform?. Kindly advise which function can be used in the final step of
> spei calculation. Many Thx..
>
> qudsia
>
>
>
>
>
>
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