	VXMATRIX sets up Matrix (0) to hold data from the first
	MAXNSAVE save bins of the current save file in a 
	velocity-x position grid.  Any contents of Matrix (0) are
	overwritten and lost.

	Syntax: VXMATRIX(dx)

	dx is the increment in the x-position direction between pixels
	on the sky (in arc seconds).  The x-position is from the
	XSOURCE header word.

	MAXNSAVE is a global adverb that must be set prior to
	using this procedure (e.g. via PRCSTK or by hand).

	The velocity increment in the matrix is taken from the
	the velocity increment at the center of the spectra of the
	first scan in the save file (NSAVE=1).

	The coordinate system for the first axis of Matrix (0) will
	be VELOCITY and the coordinate system for the second
	axis of Matrix (0) will be chosen based on the value of
	the COORDCD header word of the NSAVE=1 scan.

	If H0(COORDCD) is "GALACTIC" then the second axis of the
	matrix will have the coordinate label "GLON".  If the last 4 
	characters of H0(COORDCD) for NSAVE=1 are "RADC" then the 
	coordinate label will be "RA" otherwise the coordinate label 
	will be "X-AXIS".

	It is intended that the use of VXMATRIX be followed by the
	use of VXGRID to grid the same data.

	File name: vxmatrix.prc

	This procedure is included in maps.plib

	Example:

	You have a save file with data from NSAVE=1 through 
	NSAVE=120 and you want to make a velocity-x position map.
	The data are separated in X by 30 arc seconds.
	

		> MAXNSAVE=120
		> VXMATRIX(30)
		> VXGRID

	Note that VXGRID uses Matrix(3) to handle the averaging in
	Y-coordinate at each V-X coordinate.
