# galpy.df.evolveddiskdf.vmomentsurfacemass¶

evolveddiskdf.vmomentsurfacemass(R, n, m, t=0.0, nsigma=None, deg=False, epsrel=0.01, epsabs=1e-05, phi=0.0, grid=None, gridpoints=101, returnGrid=False, hierarchgrid=False, nlevels=2, print_progress=False, integrate_method='dopr54_c', deriv=None)[source]

Calculate the an arbitrary moment of the velocity distribution at (R,phi) times the surfacmass

Parameters:
• R (float) – Radius at which to calculate the moment (in natural units).

• phi (float, optional) – Azimuth (rad unless deg=True).

• n (int) – vR^n.

• m (int) – vT^m.

• t (float, optional) – 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).

• nsigma (float, optional) – Number of sigma to integrate the velocities over (based on an estimate, so be generous, but not too generous).

• deg (bool, optional) – Azimuth is in degree (default=False).

• epsrel (float, optional) – scipy.integrate keyword (the integration calculates the ratio of this vmoment to that of the initial DF).

• epsabs (float, optional) – scipy.integrate keyword (the integration calculates the ratio of this vmoment to that of the initial DF).

• grid (bool, optional) – 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; if this was created for a list of times, moments are calculated for each time.

• gridpoints (int, optional) – Number of points to use for the grid in 1D (default=101).

• returnGrid (bool, optional) – If True, return the grid object (default=False).

• hierarchgrid (bool, optional) – If True, use a hierarchical grid (default=False).

• nlevels (int, optional) – Number of hierarchical levels for the hierarchical grid.

• print_progress (bool, optional) – If True, print progress updates.

• integrate_method (str, optional) – orbit.integrate method argument.

• deriv (str, optional) – None, ‘R’, or ‘phi’: calculates derivative of the moment wrt R or phi onnly with grid options.

Returns:

<vR^n vT^m x surface-mass> at R,phi (no support for units).

Return type:

float or numpy.ndarray

Notes

• grid-based calculation is the only one that is heavily tested (although the test suite also tests the direct calculation)

• 2011-03-30 - Written - Bovy (NYU)