vice.singlezone.eta
===================

Type : real number or ``<function>``

Default : 2.5

The mass loading factor, defined as the ratio of the mass outflow
rate to the star formation rate.

.. math:: \eta \equiv \frac{\dot{M}_\text{out}}{\dot{M}_\star}

.. note::

	If the attribute ``smoothing`` is nonzero, this relationship
	generalizes to

	.. math:: \dot{M}_\text{out} = \eta(t)
		\langle\dot{M}_\star\rangle_{\tau_\text{s}} =
		\Bigg \lbrace {
		\frac{\eta(t)}{t}\int_0^t \dot{M}_\star(t') dt'
		(t < \tau_\text{s})
		\atop
		\frac{\eta(t)}{\tau_\text{s}}\int_{t - \tau_\text{s}}^t
		\dot{M}_\star(t') dt'\ (t \geq \tau_\text{s})
		}

	where :math:`\tau_\text{s}` is the value of the attribute, the
	outflow smoothing time.

	Note also that the time-average is over the star formation rate
	only, and not the mass-loading factor.

.. note::

	Saving this functional attribute with VICE outputs requires the
	package dill_, an extension to ``pickle`` in the Python_ standard
	library. It is recommended that VICE user's install dill_
	>= 0.2.0.

	.. _dill: https://pypi.org/project/dill/
	.. _Python: https://docs.python.org/library/

Example Code
------------
>>> import vice
>>> sz = vice.singlezone(name = "example")
>>> sz.eta = 2
>>> def f(t):
	if t <= 2:
		return 5
	else:
		return 1
>>> sz.eta = f