/frames 31 def 

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

/hsort
 { /incr exch def 
   incr 1 N 1 sub 
    { /lll exch def  
      lll incr neg incr { /xxx exch def 
                 xxx incr sub xxx compare { exit } if 
                 xxx xxx incr sub compareswap 
                 /xxx xxx incr sub def
               } for 
      xxx lll SUBFILEx 
    } 
  for } def

/SUBFILEx
 {
  /rr exch def /ll exch def 
  LL 1 RR
    {
      dup dup dup
      ll incr sub le exch rr gt or exch rr exch sub incr mod 0 ne or { SqGrL }{ SqWhL } ifelse
      exch PT
    } for
  nextframe
  } def

LL RR SUBFILE
13 hsort nextframe
4 hsort nextframe
1 hsort 
LL RR SUBFILE


----------------------------
T 22.7pc Shellsort example

Sorting a file by 13-sorting \itpc{top}, then 4-sorting \itpc{middle}, 
then 1-sorting \itpc{bottom} does not involve many
comparisons (as indicated by the unshaded elements).  The last
pass is just insertion sort, but no element has to move very far
because of the order in the file due to the first two passes.