opa
 define TeX_strings 1
 expand 1.01 window 1 1 1 1 
 limits 800 1200 0.4 1.1 erase ctype default expand 1.3
 box xlabel \lambda (\AA)
 ylabel <Opacity> 
 relocate (6000 31500) label Lyman absorption by IGM (Madau 1995)
 data OPACITY.dat read { z 1 n 2.s }
 define lfuv   1550
 define lfoca  2010
 define lnuv   2300
 set lfuv  = 1550
 set ofuv  = 1
 set zuv   = 0
 set lfoca = 2010
 set ofoca  = 1
 set lnuv  = 2300
 set onuv  = 1
 set zuv2   = 0
 do i = 1, DIMEN(n),2 {
   define file (n[$i-1])
   define zobs (z[$i-1])
  if (z[$i-1]<=2.2) { echo $zobs $file
  data $file read {l 1 o 2} connect l o 
  define lobs  ($lfuv/(1+$zobs))
  set ls = l if ( ABS(l-$lobs)<.5 )  
  set os = o if ( ABS(l-$lobs)<0.5 )
  set zs = l*0 + $zobs if ( ABS(l-$lobs)<0.5 )
  set lfuv = lfuv concat ls  
  set ofuv = ofuv concat os  
  set zuv  = zuv concat zs  
  define lobs  ($lfoca/(1+$zobs))
  set ls = l if ( ABS(l-$lobs)<1 )  
  set os = o if ( ABS(l-$lobs)<1 )
  set lfoca = lfoca concat ls  
  set ofoca = ofoca concat os  
  define lobs  ($lnuv/(1+$zobs))
  set ls = l if ( ABS(l-$lobs)<=.5 )  
  set os = o if ( ABS(l-$lobs)<=.5 )
  set zs = l*0 + $zobs if ( ABS(l-$lobs)<=0.5 )
  set lnuv = lnuv concat ls  
  set onuv = onuv concat os  
  set zuv2  = zuv2 concat zs  
		 }
			}
  ctype blue    connect lfuv  ofuv
  ptype 20 3    points  lfuv  ofuv
  do i = 1,DIMEN(lfuv)-7 {  define z (sprintf('%3.1f',zuv[$i-1]))
   define x (lfuv[$i-1]-30)  define y (ofuv[$i-1]+0.02)
  relocate $x $y  label $z
			}
  define y ($y-0.1) relocate $x $y label FUV 
  ctype yellow  connect lfoca ofoca
  ptype 20 3    points  lfoca ofoca   
  ctype red     connect lnuv  onuv
  ptype 20 3   points  lnuv  onuv   
 do i = 1,DIMEN(lnuv)-3 {  define z (sprintf('%3.1f',zuv2[$i-1]))
   define x (lnuv[$i-1]+10)  define y (onuv[$i-1]-0.02)
  relocate $x $y  label $z
			}
	label  = Z
  define y ($y-0.1) relocate $x $y label NUV 
  ctype default