{"work":{"id":"a5df2b88-b84f-4a1c-a8a7-7de010e312e1","openalex_id":null,"doi":null,"arxiv_id":"1104.2933","raw_key":null,"title":"The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes","authors":null,"authors_text":"Diego Blas, Julien Lesgourgues, Thomas Tram","year":2011,"venue":"astro-ph.CO","abstract":"Boltzmann codes are used extensively by several groups for constraining cosmological parameters with Cosmic Microwave Background and Large Scale Structure data. This activity is computationally expensive, since a typical project requires from 10'000 to 100'000 Boltzmann code executions. The newly released code CLASS (Cosmic Linear Anisotropy Solving System) incorporates improved approximation schemes leading to a simultaneous gain in speed and precision. We describe here the three approximations used by CLASS for basic LambdaCDM models, namely: a baryon-photon tight-coupling approximation which can be set to first order, second order or to a compromise between the two; an ultra-relativistic fluid approximation which had not been implemented in public distributions before; and finally a radiation streaming approximation taking reionisation into account.","external_url":"https://arxiv.org/abs/1104.2933","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-24T21:26:22.867099+00:00","pith_arxiv_id":"1104.2933","created_at":"2026-05-10T10:09:06.713990+00:00","updated_at":"2026-05-24T21:26:22.867099+00:00","title_quality_ok":true,"display_title":"The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes","render_title":"The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes"},"hub":{"state":{"work_id":"a5df2b88-b84f-4a1c-a8a7-7de010e312e1","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":47,"external_cited_by_count":null,"distinct_field_count":4,"first_pith_cited_at":"2018-07-17T04:05:07+00:00","last_pith_cited_at":"2026-05-20T17:46:56+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-05-29T22:50:29.763580+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"method","n":14},{"context_role":"background","n":13},{"context_role":"baseline","n":1},{"context_role":"dataset","n":1}],"polarity_counts":[{"context_polarity":"use_method","n":14},{"context_polarity":"background","n":13},{"context_polarity":"baseline","n":1},{"context_polarity":"use_dataset","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}