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).
Returns:

Value(s) of the correlation function at the input

angular separations.
Return type:

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).
Returns:

Value(s) of the correlation function at the input distance(s).