  We obtain estimates of Sgr A* accretion flow and black hole parameters by
fitting polarized sub-mm observations with spectra computed using
three-dimensional (3D) general relativistic (GR) magnetohydrodynamical (MHD)
(GRMHD) simulations. Observations are compiled from averages over many epochs
from reports in 29 papers for estimating the mean fluxes Fnu, linear
polarization (LP) fractions, circular polarization (CP) fractions, and electric
vector position angles (EVPAs). GRMHD simulations are computed with
dimensionless spins a_*=0,0.5,0.7,0.9,0.98 over a 20,000M time interval. We
perform fully self-consistent GR polarized radiative transfer using our new
code to explore the effects of spin a_*, inclination angle \theta, position
angle (PA), accretion rate Mdot, and electron temperature Te (Te is reported
for radius 6M). By fitting the mean sub-mm fluxes and LP/CP fractions, we
obtain estimates for these model parameters and determine the physical effects
that could produce polarization signatures. Our best bet model has a_*=0.5,
\theta=75deg, PA=115deg, Mdot=4.6*10^{-8}M_Sun/year, and Te=3.1*10^10K at 6M.
The sub-mm CP is mainly produced by Faraday conversion as modified by Faraday
rotation, and the emission region size at 230GHz is consistent with the VLBI
size of 37microas. Across all spins, model parameters are in the ranges
\theta=42deg-75deg, Mdot=(1.4-7.0)*10^{-8}M_Sun/year, and Te=(3-4)*10^10K.
Polarization is found both to help differentiate models and to introduce new
observational constraints on the effects of the magnetic field that might not
be fit by accretion models so-far considered.
