(extreme X-ray environments such as disks surrounding a black hole).

Momentum balance and the equation of state {#sec:eos-momentum}
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allows great flexibility in specifying the spatial distribution of the gas (and grain density). In addition to constant density and various ad hoc density laws (e.g., power law), it is also possible to allow to solve for a self-consistent density distribution based on momentum balance. In the simplest case of a static configuration with no external forces this reduces to the requirement of constant total pressure, whereas with the addition of an external force, such as continuum radiation pressure [@BFM] or gravity [@AscasibarDiaz2009], it becomes hydrostatic equilibrium. also allows the further generalization to the case of dynamic equilibrium in the presence of steady-state gas flow [@HenneyEtAl05].

In addition to the thermal pressure of the gas, also considers other contributions to the total pressure. These include trapped resonance line radiation [@Elitzur1986], ordered and disordered magnetic fields [@HenneyEtAl05; @Pellegrini2007], cosmic rays [@Shaw.G09Rotationally-Warm-Molecular-Hydrogen], and the Reynolds stress due to turbulent motions.

Some computational details
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An Open Source Project
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 is openly available on the web at the site [[](http://www.nublado.org)]{}. This includes the full source, the atomic and molecular data needed for  to operate, 