The Force-Free Electrodynamics Method for the Extrapolation of Coronal   Magnetic Fields from Vector Magnetograms
  We present a new improved version of our force-free electrodynamics (FFE) numerical code in spherical coordinates that extrapolates the magnetic field in the inner solar corona from a photospheric vector magnetogram. The code satisfies the photospheric boundary condition and the condition divB=0 to machine accuracy. The performance of our method is evaluated with standard convergence parameters, and is found to be comparable to that of other nonlinear force-free extrapolations. 
Ioannis Contopoulos
astro-ph.SR