NAME:
sigmaRT
PURPOSE:
calculate the radial-tangential co-variance of the velocity distribution at (R,phi)
INPUT:
R - radius at which to calculate the moment(/ro)
phi= azimuth (rad unless deg=True)
t= time at which to evaluate the DF (can be a list or ndarray; if this is the case, list needs to be in descending order and equally spaced)
surfacemass, meanvR, meavT= if set use this pre-calculated surfacemass and mean vR and vT
nsigma - number of sigma to integrate the velocities over (based on an estimate, so be generous)
deg= azimuth is in degree (default=False)
epsrel, epsabs - scipy.integrate keywords (the integration calculates the ration of this vmoment to that of the initial DF)
grid= if set to True, build a grid and use that to evaluate integrals; if set to a grid-objects (such as returned by this procedure), use this grid
gridpoints= number of points to use for the grid in 1D (default=101)
returnGrid= if True, return the grid object (default=False)
hierarchgrid= if True, use a hierarchical grid (default=False)
nlevels= number of hierarchical levels for the hierarchical grid
integrate_method= orbit.integrate method argument
OUTPUT:
covariance of vR and vT
HISTORY:
2011-03-31 - Written - Bovy (NYU)