INPUT:
R - radius at which to calculate this
z - height at which to calculate this
OPTIONAL INPUT:
nsigma - number of sigma to integrate the velocities over
scipy.integrate.tplquad kwargs epsabs and epsrel
mc= if True, calculate using Monte Carlo integration
nmc= if mc, use nmc samples
gl= if True, calculate using Gauss-Legendre integration
ngl= if gl, use ngl-th order Gauss-Legendre integration for each dimension