  We introduce a new one-dimensional stellar evolution code, based on the
existing Dartmouth code, that self-consistently accounts for the presence of a
globally pervasive magnetic field. The methods involved in perturbing the
equations of stellar structure, the equation of state, and the mixing-length
theory of convection are presented and discussed. As a first test of the code's
viability, stellar evolution models are computed for the components of a
solar-type, detached eclipsing binary (DEB) system, EF Aquarii, shown to
exhibit large disagreements with stellar models. The addition of the magnetic
perturbation corrects the radius and effective temperature discrepancies
observed in EF Aquarii. Furthermore, the required magnetic field strength at
the model photosphere is within a factor of two of the magnetic field strengths
estimated from the stellar X-ray luminosities measured by ROSAT and those
predicted from Ca II K line core emission. These models provide firm evidence
that the suppression of thermal convection arising from the presence of a
magnetic field is sufficient to significantly alter the structure of solar-type
stars, producing noticeably inflated radii and cooler effective temperatures.
The inclusion of magnetic effects within a stellar evolution model has a wide
range of applications, from DEBs and exoplanet host stars to the donor stars of
cataclysmic variables.
