  We have carried out WFPC2 V- and I-band imaging of the young LMC cluster NGC
2157. Construction of a color-magnitude diagram and isochrone fitting yields an
age of tau = 100 000 000 yrs, a reddening E(B-V) = 0.1 and a distance modulus
of 18.4 mag. Our data covers the mass range 0.75 < m < 5.1 solar masses. We
find that the cluster mass function changes significantly from the inner
regions to the outer regions, becoming steeper (larger number of low mass stars
relative to high mass stars) at larger radii.
  The age of NGC 2157 is comparable to its two-body relaxation timescale only
in the cluster core. The observed steepening of the mass function at larger
radii is therefore most likely an initial condition of the cluster stars. Such
initial conditions are predicted in models of cluster star formation in which
dissipative processes act more strongly upon more massive stars.
