Conjuring on an adjacency matrix
(thanks to Math::MatrixReal), this snippet
finds every couple of nodes (i, j) such that
there's a path from i to j. The matrix $sum is
called transitive closure of the graph $graph.
#!/usr/bin/perl # Transitive closure of a directed graph use strict; use Math::MatrixReal; my $n = 4; # Matrix' size my $graph = Math::MatrixReal->new_from_string( <<'MATRIX' ); [ 0 1 0 1 ] [ 0 0 1 0 ] [ 0 0 0 0 ] [ 1 1 0 0 ] MATRIX my $sum = $graph->shadow(); my $p = $graph->shadow(); $p->one(); # "One Ring to rule them all, One Ring to find them..." # Sum of A^i, for i = 0..n-1 (A is the adjacency matrix of our graph) foreach (0 .. ($n - 1)) { $p = $p * $graph; $sum = $sum + $p; } # Finished. # Now we print every couple (i, j) such that # there's a path from i to j. foreach my $i (1..$n) { foreach my $j (1..$n) { print "There's a path from $i to $j.\n" if $sum->element( $i, +$j ); } }
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Re: Transitive closure
by Zaxo (Archbishop) on Sep 10, 2001 at 17:15 UTC | |
by larsen (Parson) on Sep 11, 2001 at 11:19 UTC |
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