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.. _cosmology_io:
***********************
Cosmology I/O & Convert
***********************
.. _cosmology_io_introduction:
Introduction
============
The ``astropy.cosmology.io`` package provides a unified interface for reading, writing,
and converting |Cosmology| objects. Most of the features of this package are accessible
through the |Cosmology| class, which provides the methods |Cosmology.read|,
|Cosmology.write|, |Cosmology.to_format|, and |Cosmology.from_format| for reading,
writing, and converting |Cosmology| objects, respectively.
Getting Started: Reading and Writing
====================================
The |Cosmology| class includes two methods, |Cosmology.read| and |Cosmology.write|, that
make it possible to read from and write to files.
The registered ``read`` / ``write`` formats include "ascii.ecsv" and "ascii.html", like
for Table. Also, custom ``read`` / ``write`` formats may be registered into the Astropy
Cosmology I/O framework. For more information on the built-in formats, see
:ref:`cosmology_io_builtin`, or :ref:`cosmology_io_custom` for information on
registering custom formats.
Writing a cosmology instance requires only the file location and optionally, or if the
file format cannot be inferred, a keyword argument "format". Additional positional
arguments and keyword arguments are passed to the relevant writer methods.
.. doctest-skip::
>>> from astropy.cosmology import Planck18
>>> Planck18.write("example_cosmology.ecsv", format="ascii.ecsv")
Reading back the cosmology is done from |Cosmology|.
.. doctest-skip::
>>> from astropy.cosmology import Cosmology
>>> cosmo = Cosmology.read("example_cosmology.ecsv", format="ascii.ecsv")
>>> cosmo == Planck18
True
More specific cosmology classes can be used, providing default values for missing
information (see :ref:`cosmology_io_details`). However using the base class is safest as
it provides no default information and therefore requires the file to have all necessary
information to describe a cosmology.
To see a list of the available read/write file formats:
.. code-block:: python
>>> from astropy.cosmology import Cosmology
>>> Cosmology.read.list_formats()
Format Read Write Auto-identify
---------- ---- ----- -------------
ascii.ecsv Yes Yes Yes
ascii.html Yes Yes Yes
>>> Cosmology.write.list_formats()
Format Read Write Auto-identify
----------- ---- ----- -------------
ascii.ecsv Yes Yes Yes
ascii.html Yes Yes Yes
ascii.latex No Yes Yes
This list will include both built-in and registered 3rd-party formats.
Getting Started: Converting Formats
===================================
Reading and writing |Cosmology| objects go through intermediate representations, often a
dict or |QTable| instance. These intermediate representations are accessible through the
methods |Cosmology.to_format| / |Cosmology.from_format|.
|Cosmology.to_format| / |Cosmology.from_format| parse a Cosmology to/from
another python object. This can be useful for e.g., iterating through an MCMC
of cosmological parameters or printing out a cosmological model to a journal
format, like latex or HTML. When 3rd party cosmology packages register with
Astropy's Cosmology I/O, ``to/from_format`` can be used to convert cosmology
instances between packages!
.. EXAMPLE START: Planck18 to QTable and back
Another pre-registered format is "table", for converting a |Cosmology| to and
from a |QTable|.
.. code-block::
>>> from astropy.cosmology import Planck18
>>> ct = Planck18.to_format("astropy.table")
>>> ct
<QTable length=1>
name H0 Om0 Tcmb0 Neff m_nu Ob0
km / (Mpc s) K eV
str8 float64 float64 float64 float64 float64[3] float64
-------- ------------ ------- ------- ------- ----------- -------
Planck18 67.66 0.30966 2.7255 3.046 0.0 .. 0.06 0.04897
Now this |QTable| can be used to load a new cosmological instance identical to
the |Planck18| cosmology from which it was created.
.. code-block::
>>> cosmo = Cosmology.from_format(ct, format="astropy.table")
>>> print(cosmo)
FlatLambdaCDM(name="Planck18", H0=67.66 km / (Mpc s), Om0=0.30966,
Tcmb0=2.7255 K, Neff=3.046, m_nu=[0. 0. 0.06] eV, Ob0=0.04897)
Perhaps most usefully, |QTable| itself has ``read/write`` methods with numerous options,
e.g. FITS, that now work with |Cosmology|.
.. EXAMPLE END
To see the a list of the available conversion formats:
.. code-block:: python
>>> from astropy.cosmology import Cosmology
>>> Cosmology.to_format.list_formats()
Format Read Write Auto-identify
----------------- ---- ----- -------------
astropy.cosmology Yes Yes Yes
astropy.model Yes Yes Yes
astropy.row Yes Yes Yes
astropy.table Yes Yes Yes
mapping Yes Yes Yes
yaml Yes Yes No
This list will include both built-in and registered 3rd-party formats.
Using Cosmology I/O
===================
More details are provided in the following pages:
.. toctree::
:maxdepth: 2
details.rst
builtin.rst
custom.rst
Reference/API
=============
.. automodapi:: astropy.cosmology.connect
|
