pro convolute,spec1,spec2,step,con,yfit,xcon,aa,xpp,noplot=noplot
!p.multi=[0,1,2]
con=spec2(0:2*step-1)*0.
nel=n_elements(spec2)
sspec2=spec2(step:nel-1-step)
index=indgen(nel)
for i=0,2*step-1 do begin
sspec1=spec1(i:nel-1-2*step+i)
prod=sspec1*sspec2
con(i)=total(prod)
endfor
;plot,con
xcon=double(findgen(2*step))
con=con/max(con)
yfit=gaussfit(xcon,con,aa)
if noplot ne 1 then begin
plot,xcon,yfit,ys=1,yr=minmax([con,yfit])
oplot,xcon,con,psym=2
print,'minpoint - step=',aa(1)-step
endif
x=aa(1)
diff=1.
n0=0
while abs(diff) gt 1.e-4 do begin
z=(x-aa(1))/aa(2)
f=-z/aa(2)*aa(0)*exp(-z^2/2.)+aa(4)+2.*aa(5)*x
df=-aa(0)/aa(2)*exp(-z^2/2.)+(z/aa(2))^2*aa(0)*exp(-z^2/2.)+aa(5)*x
x1=x-f/df
n0=n0+1
;print,x1,n0,f,df,z
diff=x1-x
;print,diff,x-step
x=x1
endwhile

firstder=deriv(xcon,con)
mnd=min(firstder)
imn=!c
mxd=max(firstder)
imx=!c
if imx lt imn then zero=min(abs(firstder(imx:imn))) else zero=min(abs(firstder(imn:imx)))
izero=!c
xpp=imx+izero
vline,xpp
plot,xcon,firstder
vline,[imn,xpp,imx]
if abs(xpp-aa(1)) gt 3 then xpp=x
xyouts,xpp,1.002,string(xpp,'(i4)'),align=.5,charsize=1.5
if noplot ne 1 then print,'peak - step=',xpp-step
;stop
pm0
return
end