NAME:
	slope
 PURPOSE: (one line)
	Compute slope of a line using part of the data.
 DESCRIPTION:
	The left and right hand values are computed from the mean of the
	input data array from -width to +width about the mid-point of the
	bin.  The slope is derived from these means and the uncertainty
	comes from propagating the uncertainties.
 CATEGORY:
       Function fitting
 CALLING SEQUENCE:
	coeff=slope(a,b,width,x,y)
 INPUTS:
	a     - Mid-point of the left hand bin in units of x.
	b     - Mid-point of the right hand bin in units of x.
	width - Half-width of each bin.
	x     - Independant values of x-y relationship.
	y     - Dependant values to get slope from.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD PARAMETERS:
 OUTPUTS:
	Return value is a vector, [slope,ds], which is the slope of the
	line from a to b and ds is the uncertainty on the slope.
 COMMON BLOCKS:
 SIDE EFFECTS:
	Left, right values and slope are printed to the screen.
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
	Written by Marc W. Buie, Lowell Observatory.