How to use cylindrical coordinates while defining formulas

Hi all,

I wanted to know how can we define the cylindrical co-ordinates while using formulas for co-efficient form PDE physics. for example i had to use this equations which is having cylindrical co-ordinates (r & z) : "((10^12)exp((-((r-0)^2)/2So^2)-(-((z-0)^2)/2*So^2)))". (I have highlighted r & z here).

Is that the right way of using r & z co-ordinated ?

Many thanks in advance !!

Regards Hari