  Proteins contain a large fraction of regular, repeating conformations, called
secondary structure. A simple, generic definition of secondary structure is
presented which consists of measuring local correlations along the protein
chain. Using this definition and a simple model for proteins, the forces
driving the formation of secondary structure are explored. The relative role of
energy and entropy are examined. Recent work has indicated that compaction is
sufficient to create secondary structure. We test this hypothesis, using simple
non-lattice protein models.
