[PD] cart2sph

[bbogart at ryerson.ca]

Hello all,

I'm very confused by the values given by cart2sph in
zexy 1.1. They conflict with my original expr based
equation.

So If I have x=5, y=5 and z=5

cart2sph gives me:
r=8.66, phi=0.78, theta=0.61

In my own implementation I get:
r=8.66, theta=0.955, phi=0.78

I'm using this equation:

x^2+y^2+z^2=r^2
theta=cos^-1(z/r)
phi=tan^-1(y/x)