pro stem_plot,x1,y1,psym=psym,_EXTRA=extra

if n_params() EQ 1 then begin
	y=x1
	x=indgen(n_elements(y))
endif else begin
	y=y1
	x=x1
endelse

np=n_elements(x)<n_elements(y)
y=y[0:np-1]
y=transpose(y[*])

;Set up the x-axis so position values are tripled
xv=transpose(x[*])
xv=[xv,xv,xv]
xv=xv[*]

;Set up y so that (0,y[k],0) is used at each position.
yv=replicate(0.,3,np)
yv[1,*]=y

plot,xv,yv,_extra=extra
if keyword_set(psym) then oplot,x,y,psym=psym
end