THD calculation using FFT tool and mathematically

i used the FFT tools to compute the THD and it gave me a certain value. then, when i calculated the THD using a mathematical equation i got a different value. So, please i want to know how the FFT tools of powergui compute the THD. i.e, by which equation it calculate the THD?

Answer 1

[Wayne King]

Do you have Signal Processing Toolbox? If you do, see the function thd()

[moha]

thanks a lot for your interest. yes i have a signal processing toolbox. but i didn't find the function thd() Please, explain to me what can i do exactly? Thanks

[Wayne King]

which version of MATLAB are you using? which release?