The TeX Catalogue OnLine, Entry for subeqnarray, Ctan Edition

Equation array with sub numbering.

This package defines the subeqnarray and subeqnarray* environments, which behave like the corresponding eqnarray and eqnarray* environments, except that the individual lines are numbered like 1a, 1b, 1c, etc. To refer to these numbers an extra label command \slabel is provided.

Users are urged to consider the alignment capabilities of the amsmath bundle, which produce better results than eqnarray-related macros.