  Fix a Chern character of a stable sheaf on the plane. Assume either the rank
is at most 6 or the rank and first Chern class are coprime and the discriminant
is sufficiently large. We use recent results of Bayer and Macri on Bridgeland
stability to compute the ample cone of the moduli space of Gieseker semistable
sheaves with the given Chern character. We recover earlier results, such as
those by Stromme and Yoshioka, as special cases.
