1. Overview

Welcome to the OpenSn user manual.

OpenSn is a massively parallel discrete ordinates transport code for solving neutral-particle transport problems on modern computing platforms. The Python interface exposed by OpenSn allows users to build meshes, assign materials, define angular quadratures and groupsets, configure source-driven or eigenvalue-based transport problems, and postprocess the resulting solutions.

This manual is intended to teach you how to use OpenSn effectively and how to write your own inputs to solve steady-state, time-dependent, adjoint, and criticality transport problems.

The guide is organized around the pieces of a typical OpenSn workflow:

  • build or import a mesh,

  • assign materials and sources,

  • choose quadratures and groupsets,

  • define a transport problem,

  • choose and run a solver,

  • inspect and export the results.

The emphasis throughout is practical use. The goal is not just to list Python APIs, but to explain how the pieces fit together and how to make sensible choices when building real transport models.

If you are new to OpenSn, a good path through the manual is:

  1. read OpenSn Basics,

  2. read the mesh, materials, quadrature, and groupset sections,

  3. read the problem and solver sections,

  4. work through Example Problems,

  5. then use the postprocessing and best-practices sections as needed.

Note

OpenSn has many options, but most inputs reduce to a small set of core ideas: mesh, materials, groupsets, a problem object, and a solver object. Once those pieces are clear, the rest of the manual becomes much easier to navigate.