NAME:
sigma2
PURPOSE:
calculate sigma_R^2 at R by marginalizing over velocity
INPUT:
R - radius at which to calculate sigma_R^2 density (/ro)
OPTIONAL INPUT:
nsigma - number of sigma to integrate the velocities over
KEYWORDS:
romberg - if True, use a romberg integrator (default: False)
OUTPUT:
sigma_R^2 at R
HISTORY:
2010-03-XX - Written - Bovy (NYU)