An Empirical Mass Function Distribution
  The halo mass function, encoding the comoving number density of dark matter
halos of a given mass, plays a key role in understanding the formation and
evolution of galaxies. As such, it is a key goal of current and future deep
optical surveys to constrain the mass function down to mass scales which
typically host $L_\star$ galaxies. Motivated by the proven accuracy of
Press-Schechter-type mass functions, we introduce a related but purely
empirical form consistent with standard formulae to better than 4\% in the
medium-mass regime, $10^{10}-10^{13} h^{-1}M_\odot$. In particular, our form
consists of 4 parameters, each of which has a simple interpretation, and can be
directly related to parameters of the galaxy distribution, such as $L_\star$.
  Using this form within a hierarchical Bayesian likelihood model, we show how
individual mass-measurement errors can be successfully included in a typical
analysis whilst accounting for Eddington bias. We apply our form to a question
of survey design in the context of a semi-realistic data model, illustrating
how it can be used to obtain optimal balance between survey depth and angular
coverage for constraints on mass function parameters.
  Open-source {\tt Python} and {\tt R} codes to apply our new form are provided
at \url{http://mrpy.readthedocs.org} and
\url{https://cran.r-project.org/web/packages/tggd/index.html} respectively.
