Computational packages for Cosmologists

The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the "Big Bang" of cosmology. The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. Therefore, analysis of the small anisotropies in the CMB helps us to understand the origin and the fate of our universe. In past few decades, there has been a lot of improvement in the observations and several experiments, performed to understand the basic structure of the universe. For analyzing data of different cosmological experiments and for understanding the theoretical nature of the universe many advanced methods and computing software are developed in and used by Cosmologists for years. These software are widely used by the cosmologists across the globe.
The computational software, used in cosmology can be classified into the following major classes.
* Map generation and processing software: These software are used for preparing the CMB sky maps from the crude observational data. The software HEALPIX is used for map generation and processing.
* Cosmological Boltzmann codes: These codes are used for calculating the theoretical power spectrum given the cosmological parameters. These codes are capable of calculating the power spectrum from the standard LCDM model or its derivatives. Some of the most used CMB Boltzmann codes are CMBFAST, CAMB, CMBEASY, CLASS, CMBAns etc.
* Cosmological parameter estimator: The parameter estimation codes are used for calculating the best-fit parameters from the observation data. The ready to used codes available for this purpose are CosmoMC, AnalyzeThis etc.
HEALPix
HEALPix (sometimes written as Healpix), an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, can refer to either an algorithm for pixelization of the 2-sphere, an associated software package, or an associated class of map projections. Healpix is widely used for cosmological random map generation. The original motivation for devising HEALPix was one of necessity. NASA's WMAP and ESA’s mission Planck - produce multi-frequency data sets sufficient for the construction of full-sky maps of the microwave sky at an angular resolution of a few arc minutes. The principal requirements in the development of HEALPix were to create a mathematical structure that supports a suitable discretization of functions on a sphere at sufficiently high resolution, and to facilitate fast and accurate statistical and astrophysical analysis of massive full-sky data sets. The HEALPix maps are used in almost all the data processing research in cosmology.
CMBFAST
CMBFAST is a computer code, written by Uros Seljak and Matias Zaldarriaga, for computing the power spectrum of the cosmic microwave background anisotropy. It is the first efficient program to do so, reducing the time taken to compute the anisotropy from several days to a few minutes by using a novel semi-analytic line-of-sight approach.
CAMB
Code for Anisotropies in the Microwave Background by Antony Lewis and Anthony Challinor. The code was originally based on CMBFAST. Later several developments are made to make it a faster and more accurate and compatible with the present research. The code is written in an object oriented manner to make it more user friendly.
CMBEASY
CMBEASY is a software package written by Michael Doran, Georg Robbers and Christian M. Müller. The code is based on the CMBFAST package. CMBEASY is fully object oriented C++. This considerably simplifies manipulations and extensions of the CMBFAST code. In addition, a powerful Spline class can be used to easily store and visualize data. Many features of the CMBEASY package are also accessible via a graphical user interface. This may be helpful for gaining intuition, as well as for instruction purposes.
CLASS
CLASS is a new Boltzmann code developed in this line. The purpose of CLASS is to simulate the evolution of linear perturbations in the universe and to compute CMB and large scale structure observables. Its name also comes from the fact that it is written in object-oriented style mimicking the notion of class. Classes are a wonderful programming feature available e.g. in C++ and python, but these languages are known to be less vectorizable/parallelizable than plain C (or Fortran), and hence potentially slower. For CLASS we choose to use plain C for high performances, while organizing the code in a few modules that reproduce the architecture and philosophy of C++ classes, for optimal readability and modularity.
CosmoMC
CosmoMC is a Fortran 2003 Markov-Chain Monte-Carlo (MCMC) engine for exploring cosmological parameter space, together with code for analysing Monte-Carlo samples and importance sampling (plus a suite of python scripts for building grids of runs and plotting and presenting results). The code does brute force (but accurate) theoretical matter power spectrum and Cl calculations with CAMB.
AnalizeThis
AnalizeThis is a parameter estimation package used by cosmologists. It comes with the CMBEASY package. The code is written in C++ and uses the global metropolis Algorithm for estimation of cosmological parameters.

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