  We begin by reviewing Zhu's theorem on modular invariance of trace functions
associated to a vertex operator algebra, as well as a generalisation by the
author to vertex operator superalgebras. This generalisation involves objects
that we call `odd trace functions'. We examine the case of the N=1
superconformal algebra. In particular we compute an odd trace function in two
different ways, and thereby obtain a new representation theoretic
interpretation of a well known classical identity due to Jacobi concerning the
Dedekind eta function.
