SSCache 1.0

REQUIREMENTS: VMD Version 1.0 or greater

	Calculates and stores the secondary structure assignment for
	each timestep.  This lets you see how the secondary structure
	changes over a trajectory.

	It is turned on with the command "start_sscache" followed by the
	molecule number of the molecule whose secondary structure should be
	saved (the default is "top", which gets converted to the correct
	molecule index).  Whenever the frame for that molecule changes, the
	procedure "sscache" is called.

	"sscache" is the heart of the script.  It checks if a secondary
	structure definition for the given molecule number and frame already
	exists in the Tcl array sscache_data(molecule,frame).  If so, it uses
	the data to redefine the "structure" keyword values (but only for
	the protein residues).  If not, it calls the secondary structure
	routine to evaluate the secondary structure based on the new
	coordinates.  The results are saved in the sscache_data array.

	Once the secondary structure values are saved, the molecule can be
	animated rather quickly and the updates can be controlled by the
	animate form.

	To turn off the trace, use the command "stop_sscache", which
	also takes the molecule number.  There must be one "stop_sscache"
	for each "start_sscache".  The command "clear_sscache" resets
	the saved secondary structure data for all the molecules and all the
	start_sscache molid - start caching the given molecule
	stop_sscache molid - stop caching
	reset_sscache - reset the cache
	sscache - internal function used by trace

  All versions of VMD:

  VMD 1.4 users must also download (and source) this file, for sscache to work:

	Andrew Dalke (