  We describe a unique approach to economizing the solution to the general
chemical equilibrium and equation-of-state problem for late-type stars,
including diatomic and polyatomic molecules, that is fast, accurate, and
suitable for responsive approximate data modelling applications, and to more
intensive modelling approaches in which the calculation of the gas equilibrium
must be expedited to allow other aspects to be treated more realistically. The
method, based on a novel economization of the Newton's method of solution of
the linearized Saha and conservation equations, has been implemented in Python
and made available as a stand-alone package, GASPy, and has been integrated
into the interactive Python atmosphere and spectrum modelling code
ChromaStarPy. As a result, ChromaStarPy now computes the state of the gas, the
number density of absorbers, and the surface flux spectrum, with consistent
inclusion of 105 chemical species, including 34 diatomic, and 16 polyatomic,
neutral molecules, as well as H$^-$ and H$_2^+$, as well as many neutral and
ionized atomic species. The economized method converges very rapidly and
greatly improves the code's relevance to late-type stellar and brown dwarf
spectrum modelling. We provide a brief overview of the GAS methodology, and
present some illustrative results for the chemical equilibrium and spectrum for
an M-type bright giant and dwarf, and a comparison to results of the
PHOENIX/PPRESS package. All codes are available from the OpenStars www site:
www.ap.smu.ca/OpenStars.
