BAR_GRAPH Name
 	BAR_GRAPH
Purpose
 	This procedure plots bar graphs.
Category
 	Graphics
Calling Sequence
 	BAR_GRAPH, [Xval,] Yval
Inputs
	Yval:  A vector of values to be plotted, of type integer or
	       floating point. Optional Inputs
	Xval:  A vector of ordinate values for the plot, of type integer
	       or floating point.
Keyword Parameters
	BARBORDER:  The color of the border of the bars.  The default is the
		same as BARCOLOR.
	BARCOLOR:  The color of the bars of the bar plot.
	BARGAP:  The size of the gap between bars in unit of fraction of the
		bar width.  The default is 0 (no gap).
	CHARSIZE:  The size of the text characters.
	COLOR:  The color of the plot axes and text.
	FONT:  The index of the font table to be used.
	OVERPLOT:  If set the procedure plots on top of the exising plot.
	SUBTITLE:  A subtitle for the plot, of type string.
	TITLE:  A title, of type string, for the plot.
	VARWIDTH:  If set the bars are all with variable widths such that
		there are no gaps between them.  The default is to plot all
		bars with the same width.
	[X,Y]MINOR:  The number of minor tick marks between major tick marks.
	[X,Y]RANGE:  A 2-element vector containing the minimum and maximum
		X- or Y-coordinates to be plotted.
	[X,Y]STYLE:  See the IDL help for the use of these keywords in plotting
		routines. 
	[X,Y]THICK:  The line thickness.
	[X,Y]TICKLEN:  The length of the ticks on the X- or Y-axis, in units of
		fraction of the window size.  The default is !p.ticklen (0.02).
	[X,Y]TICKNAME:  A vector, of type string, of labels for the major ticks
		on the X- or Y-axis.  There should be [X,Y]TICKS + 1 values in
		the vector.
	[X,Y]TICKS:  The number of major ticks on the X- or Y-axis minus one.
	[X,Y]TICKV:  The location of the major ticks on the X- or Y-axis.
	[X,Y]TITLE:  A label for the X or Y axis, of type string.
Uses
 	FIRST_DIFF.pro 
	VAR_TYPE.pro
Procedure
	This procedure uses the POLYFILL procedure to draw solid bar 
	graphs.
Example
 	Plot 10 step-like bars.
	  bar_graph, indgen(10)+1, barcolor=2, bargap=0.1
Modification History
  
 	Written by:	Daithi A. Stone (stoned@atm.ox.ac.uk), 2000-09-11.
	Modified:	DAS, 2001-10-22 (Added [X,Y]TICKLEN keywords).
	Modified:	DAS, 2003-06-16 (added FONT, [X,Y]MINOR, [X,Y]THICK
			keywords)