;+ NAME:
;      CENTERMASS
;
; PURPOSE:
;      A function which returns the center of mass of datav
;
; CALLING SEQUENCE:
;      Result = EXTRACTFUNC (XVALS, DATAV, VARV, SPECV)
;
; INPUTS:
;      XVALS: The x values for the data
;      DATAV: The sky subtracted data
;      VARV:  The variance
;      SPECV: The spectrum
;
; OUTPUTS:
;
;
; MODIFICATION HISTORY:
;
;		 Written by: John Dermody, 22 Sep 2003
;
;       Thu Dec 18 22:53:00 2003, John Dermody
;              cleaned up a bit
;-

function centermass, xvals, datav, varv, specv

return, total(xvals * (datav / specv))

end