vice.milkyway.evolution
=======================

Type : ``<function>``

Default : vice.milkyway.default_evolution

As a function of radius in kpc and time in Gyr, respectively, either
the surface density of gas in :math:`M_\odot kpc^{-2}`, the surface
density of star formation in :math:`M_\odot kpc^{-2} yr^{-1}`, or the
surface density of infall in :math:`M_\odot kpc^{-2} yr^{-1}`. As in
the ``singlezone`` object, the interpretation is set by the attribute
``mode``.

.. seealso:: vice.milkyway.default_evolution

.. note:: This attribute will always be expected to accept radius in
	kpc and time in Gyr as parameters, in that order. However, surface
	densities of star formation and infall will always be interpreted
	as having units of :math:`M_\odot yr^{-1} kpc^{-2}` according to
	convention.

.. note:: This is the **only** object in the current version of VICE
	which formulates an evolutionary parameter in terms of surface
	densities. This is done because many physical quantities are
	reported as surface densities in the astronomical literature. The
	``singlezone`` and ``multizone`` objects, however, formulate
	parameters in terms of mass, out of necessity for the
	implementation.

Example Code
------------
>>> import vice
>>> mw = vice.milkyway(name = "example")