# Composite PolytropesΒΆ

Composite polytropes are an extension of standard polytrope
models for stellar structure, to allow for discontinuities in the
density \(\rho\) and/or the polytropic index \(n\). This
appendix lays out the mathematical formalism1
underpinning them; it is intended to complement the Building POLY Models
appendix, which describes how composite polytrope models can be built
using the **build_poly** executable.

Footnotes

- 1
The formalism here is based on Mixed polytrope with density discontinuities (Christensen-Dalsgaard, 2015, unpublished), with extensions to allow for constant-density regions.