pro mycontour
;
;  a simple programme
;
;@colors
;npts = 256                      ; number of pts
;nsig = 4.                       ; number of sigma
x    = -nsig + findgen(npts)/float(npts)*2*nsig
Gs   = fltarr(npts,npts)
for j=0,npts-1 do begin 
    for i=0,npts-1 do begin 
        Gs[i,j] = exp(-(x[i]^2+x[j]^2)/2.) 
    endfor  
endfor
;
contour,Gs,x,x,nlev=255,/iso,/fill
end