Skip to content

Basic usage

Jump to bottom
vrastil edited this page Nov 10, 2016 · 5 revisions

This document contains basic information about used structures and functions. At the end of document is provided code which implements these basic functions (also in tests/min_code.c).

Cosmological parameters

Start by defining cosmological parameters defined in structure ccl_parameters. This structure (exact definition in include/ccl_core.h) contains densities of matter, parameters of dark energy (w0, wa), Hubble parameters, primordial poer spectra, radiation parameters, derived parameters (sigma_8, Omega_1, z_star) and modified growth rate.

You can initialize this structure through function ccl_parameters_create which returns object of type ccl_parameters.

ccl_parameters ccl_parameters_create(
	double Omega_c, double Omega_b, double Omega_k, double Omega_n, double w0, double wa, double h,
	double A_s, double n_s, int nz_mgrowth, double *zarr_mgrowth, double *dfarr_mgrowth
);

where:

  • Omega_c: cold dark matter
  • Omega_b: baryons
  • Omega_m: matter
  • Omega_n: neutrinos
  • Omega_k: curvature
  • little omega_x means Omega_x*h^2
  • w0: Dark energy eq of state parameter
  • wa: Dark energy eq of state parameter, time variation
  • H0: Hubble's constant in km/s/Mpc.
  • h: Hubble's constant divided by (100 km/s/Mpc).
  • A_s: amplitude of the primordial PS
  • n_s: index of the primordial PS

For some specific cosmologies you can also use functions ccl_parameters_create_flat_lcdm, ccl_parameters_create_flat_wcdm, ccl_parameters_create_flat_wacdm, ccl_parameters_create_lcdm, which automatically set some parameters. For more information, see file include/ccl_core.c

Cosmology object

For majority of CCL`s functions you need an object of type ccl_cosmology, which can be initalize by function ccl_cosmology_create

ccl_cosmology * ccl_cosmology_create(ccl_parameters params, ccl_configuration config);

Note that the function returns a pointer. Variable params of type ccl_parameters contains cosmological parameters created in previous step. Structure ccl_configuration contains information about methods for computing transfer function, matter power spectrum and mass function (for available methods see include/ccl_config.h). For now, you should use default configuration default_config

const ccl_configuration default_config = {ccl_boltzmann_class, ccl_halofit, ccl_tinker};

After you are done working with this cosmology object, you should free its work space by ccl_cosmology_free

void ccl_cosmology_free(ccl_cosmology * cosmo);

Distances and Growth factor

With defined cosmology we can now compute distances, growth factor (and rate) or sigma_8. For comoving radial distance you can call function ccl_comoving_radial_distance

double ccl_comoving_radial_distance(ccl_cosmology * cosmo, double a);

which returns distance to scale factor a in units of Mpc. For luminosity distance call function ccl_luminosity_distance

double ccl_luminosity_distance(ccl_cosmology * cosmo, double a);

which also returns distance in units of Mpc. For growth factor (normalized to 1 at z = 0) at sale factor a call ccl_growth_factor

double ccl_growth_factor(ccl_cosmology * cosmo, double a);

For more routines to compute distances and growth rates (e.g. at multiple times at once) see file include/ccl_background.h

Matter power spectra and sigma_8

For given cosmology we can compute linear and non-linear matter power spectra using functions ccl_linear_matter_power and ccl_nonlin_matter_power

double ccl_linear_matter_power(ccl_cosmology * cosmo, double a, double k);
double ccl_nonlin_matter_power(ccl_cosmology * cosmo, double a, double k);

Sigma_8 can be calculated by function ccl_sigma8, or more generally by function ccl_sigmaR, which computes the variance of the density field smoothed by spherical top-hat window function on a comoving distance R (in Mpc).

double ccl_sigmaR(ccl_cosmology *cosmo, double R);
double ccl_sigma8(ccl_cosmology *cosmo);

These and other functions for different matter power spectra can be found in file include/ccl_power.h.

Example code

This code can also be found in tests/min_code.h You can run the following example code. For this you will need to compile with:

gcc -Wall -Wpedantic -g -O0 -I./include -std=c99 -fPIC tests/min_code.c -o tests/min_code -L./lib -L/usr/local/lib -lgsl -lgslcblas -lm -Lclass -lclass -lccl
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "ccl.h"

#define OC 0.25
#define OB 0.05
#define OK 0.00
#define ON 0.00
#define HH 0.70
#define W0 -1.0
#define WA 0.00
#define NS 0.96
#define AS 2.1E-9
#define ZD 0.5

int main(int argc,char **argv){
    // Initialize cosmological parameters
    ccl_parameters params=ccl_parameters_create(OC,OB,OK,ON,W0,WA,HH,AS,NS,-1,NULL,NULL);
    
    // Initialize cosmology object given cosmo params
    ccl_cosmology *cosmo=ccl_cosmology_create(params,default_config);
    
    // Compute radial distances
    printf("Comoving distance to z = %.3lf is chi = %.3lf Mpc\n",
		ZD,ccl_comoving_radial_distance(cosmo,1./(1+ZD)));
	printf("Luminosity distance to z = %.3lf is chi = %.3lf Mpc\n",
		ZD,ccl_luminosity_distance(cosmo,1./(1+ZD)));
		
	// Compute growth factor and growth rate
	printf("Growth factor and growth rate at z = %.3lf are D = %.3lf and f = %.3lf\n",
		ZD, ccl_growth_factor(cosmo,1./(1+ZD)),ccl_growth_rate(cosmo,1./(1+ZD)));  
		
    // Compute sigma_8
	printf("* sigma_8 = %.3lf\n", ccl_sigma8(cosmo));
	
	//Always clean up!!
	ccl_cosmology_free(cosmo);

	return 0;
}
Clone this wiki locally