.. sectionauthor:: Duncan Macleod <duncan.macleod@ligo.org>

.. currentmodule:: gwpy.table.lsctables

Calculating (and plotting) event rate versus time
#################################################

I would like to study the rate at which event triggers are generated by the
`ExcessPower` gravitational-wave burst detection algorithm, over a small
stretch of data.

The data from which these events were generated are a simulation of Gaussian noise
with the Advanced LIGO design spectrum, and so don't actually contain any real
gravitational waves, but will help tune the algorithm to improve detection of
future, real signals.



First, import the `SnglBurstTable`:

.. code-block:: python

   from gwpy.table.lsctables import SnglBurstTable


and read a table of (simulated) events:

.. code-block:: python

   events = SnglBurstTable.read('../../gwpy/tests/data/'
                                'H1-LDAS_STRAIN-968654552-10.xml.gz')


We can calculate the rate of events (in Hertz) using the :meth:`~SnglBurstTable.event_rate` method:

.. code-block:: python

   rate = events.event_rate(1, start=968654552, end=968654562)


The :meth:`~SnglBurstTable.event_rate` method has returned a :class:`~gwpy.timeseries.TimeSeries`, so we can display this using the :meth:`~gwpy.timeseries.TimeSeries.plot` method of that object:

.. code-block:: python

   plot = rate.plot()
   plot.set_xlim(968654552, 968654562)
   plot.set_ylabel('Event rate [Hz]')
   plot.set_title('LIGO Hanford Observatory event rate for GW100916')
   plot.show()

.. plot:: ../examples/table/rate.py