# pyccl.correlation module¶

Correlation functon computations.

Choices of algorithms used to compute correlation functions:
‘Bessel’ is a direct integration using Bessel functions. ‘FFTLog’ is fast using a fast Fourier transform. ‘Legendre’ uses a sum over Legendre polynomials.
pyccl.correlation.correlation(cosmo, ell, C_ell, theta, corr_type='gg', method='fftlog')[source]

Compute the angular correlation function.

Parameters: cosmo (Cosmology) – A Cosmology object. ell (array_like) – Multipoles corresponding to the input angular power spectrum. C_ell (array_like) – Input angular power spectrum. theta (float or array_like) – Angular separation(s) at which to calculate the angular correlation function (in degrees). corr_type (string) – Type of correlation function. Choices: ‘GG’ (galaxy-galaxy), ‘GL’ (galaxy-shear), ‘L+’ (shear-shear, xi+), ‘L-‘ (shear-shear, xi-). method (string, optional) – Method to compute the correlation function. Choices: ‘Bessel’ (direct integration over Bessel function), ‘FFTLog’ (fast integration with FFTLog), ‘Legendre’ ( brute-force sum over Legendre polynomials). Value(s) of the correlation function at the input angular separations. float or array_like
pyccl.correlation.correlation_3d(cosmo, a, r)[source]

Compute the 3D correlation function.

Parameters: cosmo (Cosmology) – A Cosmology object. a (float) – scale factor. r (float or array_like) – distance(s) at which to calculate the 3D correlation function (in Mpc). Value(s) of the correlation function at the input distance(s).
pyccl.correlation.correlation_3dRsd(cosmo, a, s, mu, beta, use_spline=True)[source]
Compute the 3DRsd correlation function using linear approximation

with multipoles.

Args:
cosmo (Cosmology): A Cosmology object. a (float): scale factor. s (float or array_like): distance(s) at which to calculate the
3DRsd correlation function (in Mpc).
mu (float): cosine of the angle at which to calculate the 3DRsd
correlation function (in Radian).
beta (float): growth rate divided by galaxy bias. use_spline: switch that determines whether the RSD correlation
function is calculated using global splines of multipoles.
Returns:
Value(s) of the correlation function at the input distance(s) & angle.
pyccl.correlation.correlation_3dRsd_avgmu(cosmo, a, s, beta)[source]

Compute the 3DRsd correlation function averaged over mu at constant s.

Args:
cosmo (Cosmology): A Cosmology object. a (float): scale factor. s (float or array_like): distance(s) at which to calculate the 3DRsd
correlation function (in Mpc).
beta (float): growth rate divided by galaxy bias.
Returns:
Value(s) of the correlation function at the input distance(s) & angle.
pyccl.correlation.correlation_multipole(cosmo, a, beta, l, s)[source]

Compute the correlation multipoles.

pyccl.correlation.correlation_pi_sigma(cosmo, a, beta, pie, sig, use_spline=True)[source]

Compute the 3DRsd correlation in pi-sigma space.

Args:
cosmo (Cosmology): A Cosmology object. a (float): scale factor. pie (float): distance times cosine of the angle (in Mpc). sig (float or array_like): distance(s) times sine of the
angle (in Mpc).
beta (float): growth rate divided by galaxy bias.
Returns:
Value(s) of the correlation function at the input pi and sigma.
pyccl.correlation.correlation_spline_free()[source]

Clear the global splines created from if ‘use_spline’ was set to True.