  M dwarfs are the most common type of star in the Galaxy, and because of their
small size are favored targets for searches of Earth-sized transiting
exoplanets. Current and upcoming all-sky spectroscopic surveys, such as the
Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), offer an
opportunity to systematically determine physical properties of many more M
dwarfs than has been previously possible. Here we present new effective
temperatures, radii, masses, and luminosities for 29,678 M dwarfs with spectral
types M0-M6 in the first data release (DR1) of LAMOST. We derived these
parameters from the supervised machine learning code, The Cannon, trained with
1,388 M dwarfs in the Transiting Exoplanet Survey Satellite (TESS) Cool Dwarf
Catalog that were also present in LAMOST with high signal-to-noise ratio
($>$250) spectra. Our validation tests show that the output parameter
uncertainties are strongly correlated with the signal-to-noise of the LAMOST
spectra, and we achieve typical uncertainties of 110 K in Teff ($\sim$3%),
0.065 $R_{\odot}$ ($\sim$14%) in radius, 0.054 $M_{\odot}$ ($\sim$12%) in mass,
and 0.012 $L_{\odot}$ ($\sim$20%) in luminosity. The model presented here can
be rapidly applied to future LAMOST data releases, significantly extending the
samples of well-characterized M dwarfs across the sky using new and exclusively
data-based modeling methods.
