/wideflag 1 def /frames 5 def /figflag 2 def 

%include /u/rs/book3/pslib/tools.ps
%include /u/rs/book3/pslib/angles.ps


/shellsort
 { 
   { /inc exch def 
     1 1 N {inc neg inc 1 add {dup inc sub compareswap} for } for ARRAY
     inc 1 eq { exit } if
   } loop
 } def

N randomperm /A exch def
/A [ 0 A aload pop ] def
/LL 1 def /RR N 1 sub def

ARRAY
1 4 13 40 shellsort

----------------------------
Med 8.666pc Shellsorting a random permutation

The effect of each of the passes in Shellsort is to bring the file as a whole
closer to sorted order.
The file is first 40-sorted, then 13-sorted, then 4-sorted, then 1-sorted.
Each pass brings the file closer to sorted order.