function newdate,startdate,increment
;+
; function that returns the date string for startdate + increment 
;    days
; input 
;   startdate = datestring of the form YYMMDD
;   increment = integer ex 10 (positive or negative)
; output  
;   a date string
;-
yr=fix(strmid(startdate,0,2))
num=julday(startdate)
return,dayjul(num+increment,yr)
end