# PolyChord: nested sampling for cosmology

## TL;DR

PolyChord is a new nested sampling algorithm designed for high-dimensional cosmological parameter estimation, capable of handling multiple modes and exploiting parameter hierarchies with efficient parallelization.

## Contribution

It introduces a novel nested sampling method that uses slice sampling, handles multi-modal posteriors, and exploits parameter hierarchies, improving efficiency in high-dimensional cosmological analyses.

## Key findings

- Efficiently samples high-dimensional, multi-modal posteriors.
- Exploits parameter hierarchies for faster convergence.
- Parallelized implementation using openMPI.

## Abstract

PolyChord is a novel nested sampling algorithm tailored for high dimensional parameter spaces. In addition, it can fully exploit a hierarchy of parameter speeds such as is found in CosmoMC and CAMB. It utilises slice sampling at each iteration to sample within the hard likelihood constraint of nested sampling. It can identify and evolve separate modes of a posterior semi-independently and is parallelised using openMPI. PolyChord is available for download at: http://ccpforge.cse.rl.ac.uk/gf/project/polychord/