I wish to obtain the square of the numerical derivative of a variable $\phi(x)$, i.e. $\left(\frac{d\phi}{dx} \right)^2$. For this, I am using the central difference technique as shown below.
$$ \left(\frac{\phi(x+h)-\phi(x-h)}{2h}\right)^2.$$
However, I am unsure whether the method that I am using is correct. I am unable to find any resource regarding this. Hence, any help would be appreciated.
Thanks in advance.