NAME:
	vectorproduct
 PURPOSE:
	Calculate vector or scalar product for two vectors
 CATEGORY:
	gen/idl/toolbox/math
 CALLING SEQUENCE:
	result = vectorproduct(r1, r2 [, /unit, /cylin, /sphere, /rect, /degrees, /scalar, /angle])
 INPUTS:
	    r1	    arrays[3,*]; type: int or float
	    r1	    arrays[3,*]; type: int or float
			vectors for which the product is to be taken.
			the first dimension identifies the three coordinates: Cartesian (default),
			cylindrical or spherical.
 OPTIONAL INPUT PARAMETERS:
	    /scalar	by default the vector (cross-product) is calculated. If /scalar is set
			then the scalar product is calculated instead.
	    /angle	if set then information about the angle between the two vectors is returned:
			    for vector products sin(angle) = |r1 x r2|/|r1||r2|
			    for scalar products cos(angle) = |r1.r2|/|r1||r2|
	    /unit	if set, then a unit vector along the cross-product vector is returned
			    (keyword not used if /scalar is set)
	    /cylin, /sphere, /rect
			indicates whether input vectors are in cylindrical, spherical or rectangular
			    coordinates. If none is set then rectangular is assumed.
			    For cross-products the output vectors are in the same units as the input vectors.
	    /degrees	if set, and spherical or cylindrical coordinates are used, then the angles
			    are assumed to be in degrees (default: radians)
 OUTPUTS:
	    result  array[3,*] or array[*]  same type as input
			cross-products are returned as array[3,*] (same as the input arrays)
			scalar products or angle information are returned as array[n]
 OPTIONAL OUTPUT PARAMETERS:
 INCLUDE:
	@compile_opt.pro	    ; On error, return to caller
 CALLS: ***
	CV_COORD, InitVar, SyncArgs, SyncDims
 CALLED BY:
	PlotSolarDisk, plot3darc, sgp4_orbit_axis, unitvectors
 PROCEDURE:
 >	The arrays r1 and r2 do not necessarily have the same dimensions, i.e.
	if r1 is an array[3,n] and r2 is an array[3] then r2 is interpreted as an array[3,n]
	with all n vectors the same (SyncArgs is used to synchronize the array dimensions).
 >	Arrays r1 and r2 can have more than two dimensions, i.e. if r1 and r2 are both
	arrays[3,n,m] then the output cross-vectors also will be an array[3,n,m] while scalar
	products will be returned as array[n,m]
 MODIFICATION HISTORY:
	AUG-1999, Paul Hick (UCSD/CASS; pphick@ucsd.edu)