I have looked through available answers, but they don't seem to answer my very basic question, and I don't know how to phrase it differently.
It's a basic question because essentially I know nothing about the del-operator or gradients :)
I'd like to know how to calculate the equation
$\vec f_{pressure} = \nabla W(\vec x - \vec x_i, h)$
where W is a function that was previously used without a gradient in front of it, and has returned a scalar value, so I'm assuming it still does.
Specifically, W looks like this:
$W(\vec r,h) = \frac{15}{\pi * h^6} $ when ||r||< h and 0 otherwise
Also, in the same manner, I would like to know how to calculate the result of
$\vec f_{pressure} = \nabla^2 W(\vec x - \vec x_i, h)$
