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******************
Dispersion Measure
******************

This document describes
calculations related to the
Dispersion Measure (DM) of FRBs.

Intervening Galaxies
====================

A set of estimates for the DM from intervening
galaxies is provided.  These are based on the
analysis given in `PN17`_.  All of the analysis
is based on statistics of the damped Lya systems
(DLAs).

Approximate
-----------

An approximate average DM to a given
redshift may be calculated with the
frb.dlas.approx_avgDM() method::

    DM = approx_avgDM(1.)

This may be calucated a single or array of redshifts.
The return value is an astropy Quantity with default
unites of pc/cm^3.

.. _PN17: http://coming.soon

MonteCarlo
----------

This algorithm generates realizations of the DM values
by randomly placing intervening galaxies along a
given sightline or sightlines.  Here is an example call::

    zeval = np.array([0.,1.,2.])
    DMs = monte_DM(np.array(zeval), nrand=1000)  # Returned without units

The values returned are in units of pc/cm^3 but
without astropy units attached.
One can then perform stats on these outputs to the
heart's desire.