...
 my @flipped_hash = reverse sort {$a->[0] <=> $b->[0] } flippout %bdry;
  ...

##</code><code>##

 ...
 for my $k ( @flipped_hash ) {
    print " \$bdry{$k->[1]}{$k->[2]} = $k->[0];\n",
 }
 ...

##</code><code>##

 $bdry{1}{2} = 3;
 $bdry{3}{4} = 2;
 $bdry{2}{3} = 1;

##</code><code>##

 ...
 sub flippout {
  my %h = @_;
  my @f;
  while( my ($k,$v) = each %h ) {
     while( my ($vk,$vv) = each %$v) {
        push @f, [$vv, $k, $vk]
     }
  }
  return @f
 }
 ...