vice.milkyway.IMF
=================

Type : ``str`` [case-insensitive] or ``<function>``

Default : "kroupa"

.. versionadded:: 1.2.0
	In version >= 1.2.0, users may construct a function of mass to
	describe the IMF.

The assumed stellar initial mass function (IMF). If assigned a string,
VICE will adopt a built-in IMF. Functions must accept stellar mass as
the only parameter and are expected to return the value of the IMF at
that mass (it need not be normalized).

Built-in IMFs:

	- "kroupa" [1]_
	- "salpeter" [2]_

.. note::

	VICE has analytic solutions to the
	:ref:`cumulative return fraction <crf>` and the
	:ref:`main sequence mass fraction <msmf>` for built-in IMFs. If
	assigned a function, VICE will calculate these quantities
	numerically, increasing the required integration time.

Example Code
------------
>>> import vice
>>> mw = vice.milkyway(name = "example")
>>> mw.IMF = "salpeter"
>>> def f(m):
	if m < 0.5:
		return m**-1.2
	else:
		return m**-2.2
>>> mw.IMF = f

.. [1] Kroupa (2001), MNRAS, 322, 231
.. [2] Salpeter (1955), ApJ, 121, 161