arXiv:0810.1285 [ps, pdf, other] Title: iCosmo: an Interactive Cosmology Package Authors: Alexandre Refregier (1), Adam Amara (2), Thomas Kitching (3), Anais Rassat (1) ((1) CEA Saclay, (2) ETH Zurich, (3) Univ. Oxford) Comments: 5 Latex pages including 2 tables and 4 figures. Submitted to Astronomy and Astrophysics. Public code and further resources available at this http URL Subjects: Astrophysics (astro-ph) iCosmo is a software package to perform interactive cosmological calculations for the low redshift universe. The computation of distance measures, the matter power spectrum, and the growth factor is supported for any values of the cosmological parameters. It also performs the computation of observables for several cosmological probes such as weak gravitational lensing, baryon acoustic oscillations and supernovae. The associated errors for these observables can be derived for customised surveys, or for pre-set values corresponding to current or planned instruments. The code also allows for the calculation of cosmological forecasts with Fisher matrices which can be manipulated to combine different surveys and cosmological probes. The code is written in the IDL language and thus benefits from the convenient interactive features and scientific library available in this language. iCosmo can also be used as an engine to perform cosmological calculations in batch mode, and forms a convenient evolutive platform for the development of further cosmological modules. With its extensive documentation, it may also serve as a useful resource for teaching and for newcomers in the field of cosmology. The iCosmo package is described with various examples and command sequences. The code is freely available with documentation at this http URL, along with an interactive web interface and is part of the Initiative for Cosmology, a common archive for cosmological resources.