# Core Cosmology Library¶

The Core Cosmology Library (CCL) is a standardized library of routines to calculate basic observables used in cosmology. It will be the standard analysis package used by the LSST Dark Energy Science Collaboration (DESC).

The core functions of this package include:

• Background quantities (Hubble parameter $$H(z)$$, distances etc.).
• Linear growth factor $$D(z)$$ and growth rate $$f(z)$$.
• Linear matter power spectra $$P(k)$$ from Boltzmann codes (CLASS, CAMB) and approximate fitting functions.
• Non-linear matter power power spectra using HaloFit and the Mira-Titan Emulator.
• Approximate baryonic modifications to the matter power spectra $$\Delta^2_{\rm baryons}$$
• Angular power spectra $$C_\ell$$ and correlation functions $$\xi$$ for arbitrary combinations of tracers including number counts, shear and CMB lensing, as well as custom-made tracers.
• A comprehensive halo model framework able to combine different prescription for the halo mass function $${\rm d}n/{\rm d}M$$, halo bias $$b(M)$$, concentration-mass relation $$c(M)$$, mass definitions, and halo profiles, as well as to provide predictions for the halo-model power spectrum of arbitrary quantities.
• Support for $$\Lambda$$ CDM, and $$w_0-w_a$$ CDM cosmologies with curvature, as well as simple modified gravity extensions ($$\Delta f(z)$$ and $$\mu-\Sigma$$).

The source code is available on github at https://github.com/LSSTDESC/CCL.

Getting Started