PRO create_gauss_beam, fwhm, extent, beam
;
; creat gaussian beam
;
; fwhm in unit of pixel
; extent is size of the created array, in unit of fwhm
; beam is the output gaussian beam, with peak value of 1.0
;
; for example, if fwhm = 4, extent = 3, beam will be a 13*13 array
;


array_size = fix(fwhm*extent/2.0) *2 +1
cent_pix = fix(fwhm*extent/2.0)
beam = fltarr(array_size , array_size)
factor=alog(2.0)
hwhm=fwhm/2.0d

FOR i=0.0d,array_size-1.0d DO BEGIN
FOR j=0.0d,array_size-1.0d DO BEGIN
   beam[i,j] = exp(-factor*((i-cent_pix)^2+(j-cent_pix)^2)/(hwhm*hwhm))
ENDFOR
ENDFOR


end