.. _physics-powerSpectrum:

Linear Theory Power Spectrum
============================

Class providing the linear theory matter power spectrum :math:`P(k,t)` as a function of wavenumber :math:`k` and cosmic time :math:`t`. The power spectrum quantifies the amplitude of density fluctuations on different scales and is the fundamental statistical descriptor of the large-scale structure of the Universe. Both the dimensional form :math:`P(k)` and the dimensionless form :math:`\Delta^2(k) = k^3 P(k) / 2\pi^2` are available, along with the logarithmic slope :math:`\mathrm{d}\ln P/\mathrm{d}\ln k`.

**Default implementation:** ``powerSpectrumStandard``

Methods
-------

``power`` → ``double precision``
   Return the linear power spectrum for :math:`k=`\ ``wavenumber`` [Mpc\ :math:`^{-1}`].

   * ``double precision, intent(in ) :: wavenumber, time``

``powerDimensionless`` → ``double precision``
   Return the dimensionless linear power spectrum for :math:`k=`\ ``wavenumber`` [Mpc\ :math:`^{-1}`].

   * ``double precision, intent(in ) :: wavenumber, time``

``powerLogarithmicDerivative`` → ``double precision``
   Return the logarithmic derivative of the power spectrum, :math:`\mathrm{d}\ln P(k)/\mathrm{d}\ln k`, for :math:`k=`\ ``wavenumber`` [Mpc\ :math:`^{-1}`].

   * ``double precision, intent(in ) :: wavenumber, time``

.. _physics-powerSpectrumStandard:

``powerSpectrumStandard``
-------------------------

Provides a linear theory power spectrum class in which the power spectrum is just the transferred primordial power spectrum correctly normalized to :math:`z=0`.

**(Default implementation)**

**Methods**

* ``factors`` — Compute factors needed for tidal tensor calculation.
* ``tidalTensorGet`` — Get the tidal tensor.