;+
; NAME: product_errprop.pro
; PURPOSE:
; 	Implements the error propagation formula for the product of two
; 	numbers, assumed to have no correlation
;
; INPUTS:
; KEYWORDS:
; OUTPUTS:
;
; HISTORY:
; 	Began 2002-10-15 17:33:28 by Marshall Perrin 
;-

function product_errprop,a,b,erra,errb,ratio=ratio

	if not(keyword_set(ratio)) then prod = a*b else prod=a/b
	;print,"prod is ",prod
	;print,a,erra
	;print,(erra/a)^2,errb^2/b^2
	return,sqrt( (erra^2/a^2+errb^2/b^2))*abs(prod)
end