When a hypersurface evolves with normal veloc
ity equal
to its mean curvature plus a forcing term g(x,t), th
e generalized (viscosity)
solution may be "fattened" at some moment when is
singular. This phenomenon corresponds to nonuniqueness of codimension-on
e solutions. A specific type of geometric singularity occurs if
includes two smooth pieces, at the moment t = 0 when
the two pieces touch each other. If each piece is strictly
convex at that moment and at that point, then we show that
fattening occurs at the rate That is, for small
positive time, the generalized solution contains a ball of
of radius , but its complement meets a ball of a
larger
radius In this sense, the sharp rate of fatt
ening of
the generalized
solution is characterized. We assume that the smooth evolution of the
two pieces of considered separately, do not c
ross each other
for small positive time.