# nbodykit.cosmology.correlation¶

Functions

 pk_to_xi(k, Pk[, ell, extrap]) Return a callable function returning the correlation function multipole of degree $$\ell$$, as computed from the Fourier transform of the input $$k$$ and $$P_\ell(k)$$ arrays. xi_to_pk(r, xi[, ell, extrap]) Return a callable function returning the power spectrum multipole of degree $$\ell$$, as computed from the Fourier transform of the input $$r$$ and $$\xi_\ell(r)$$ arrays.

Classes

 CorrelationFunction(power) Evaluate the correlation function by Fourier transforming a power spectrum object, with automatic re-scaling with redshift and sigma8.
class nbodykit.cosmology.correlation.CorrelationFunction(power)[source]

Evaluate the correlation function by Fourier transforming a power spectrum object, with automatic re-scaling with redshift and sigma8.

Parameters: power (callable) – a callable power spectrum that returns the power at a given k; this should have redshift, sigma8, and cosmo attributes attrs cosmo redshift sigma8

Methods

 __call__(r[, smoothing, kmin, kmax]) Return the correlation function (dimensionless) for separations r
__call__(r, smoothing=0.0, kmin=1e-05, kmax=10.0)[source]

Return the correlation function (dimensionless) for separations r

Parameters: r (float, array_like) – the separation array in units of $$h^{-1} \mathrm(Mpc)$$ smoothing (float, optional) – the std deviation of the Fourier space Gaussian smoothing to apply to P(k) before taking the FFT kmin (float, optional) – the minimum k value to compute P(k) for before taking the FFT kmax (float, optional) – the maximum k value to compute P(k) for before taking the FFT
nbodykit.cosmology.correlation.pk_to_xi(k, Pk, ell=0, extrap=True)[source]

Return a callable function returning the correlation function multipole of degree $$\ell$$, as computed from the Fourier transform of the input $$k$$ and $$P_\ell(k)$$ arrays.

This uses the mcfit package perform the FFT.

Parameters: k (array_like) – wavenumbers where Pk is evaluated Pk (array_like) – the array holding the power spectrum multipole values ell (int) – multipole degree of the input power spectrum and the output correlation function; monopole by default extrap (bool, optional) – whether to extrapolate the power spectrum with a power law; can improve the smoothness of the FFT a spline holding the interpolated correlation function values InterpolatedUnivariateSpline
nbodykit.cosmology.correlation.xi_to_pk(r, xi, ell=0, extrap=False)[source]

Return a callable function returning the power spectrum multipole of degree $$\ell$$, as computed from the Fourier transform of the input $$r$$ and $$\xi_\ell(r)$$ arrays.

This uses the mcfit package perform the FFT.

Parameters: r (array_like) – separation values where xi is evaluated xi (array_like) – the array holding the correlation function multipole values ell (int) – multipole degree of the input correlation function and the output power spectrum; monopole by default extrap (bool, optional) – whether to extrapolate the power spectrum with a power law; can improve the smoothness of the FFT a spline holding the interpolated power spectrum values InterpolatedUnivariateSpline