  Metastable reverse-phase droplets are calculated by renormalization-group
theory by evaluating the magnetization of a droplet under magnetic field,
matching the boundary condition with the reverse phase and noting whether the
reverse-phase magnetization sustains. The maximal metastable droplet size and
the discontinuity across the droplet boundary are thus calculated as a function
of field and temperature for the Ising model in three dimensions. The method
also yields hysteresis loops for finite systems, as function of temperature and
system size.
