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fba3fda155
The implementation of digraph.rtc was incorrect (as demonstrated in the
new test case), which meant that digraph.tc was also incorrect.
library/digraph.m:
Fix the implementation of rtc (reflexive transitive closure):
- Following the algorithm used in digraph.cliques, it needs to
traverse the graph G in *reverse* depth-first order.
- To find the clique containing a vertex X, it needs to do a DFS on
the *reversed* graph to find the vertices with a path to X.
The vertices that were previously unvisited will be members of
the same clique as X.
- Previously it found the "followers" of the elements of the clique,
and the followers of those followers, then added edges from the
members of the current clique to those followers. However, that
only includes vertices two steps removed from the clique.
I have fixed it to add edges to *all* vertices reachable from
members of the clique.
Add straightforward implementations of tc and rtc for comparison.
Add some comments.
tests/hard_coded/Mmakefile:
tests/hard_coded/digraph_tc.exp:
tests/hard_coded/digraph_tc.inp:
tests/hard_coded/digraph_tc.m:
Add test case.
NEWS:
Announce the fixes.
9 lines
82 B
Plaintext
9 lines
82 B
Plaintext
[
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"A" - "B",
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"A" - "C",
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"B" - "C",
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"C" - "A",
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"B" - "X",
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"X" - "Y"
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].
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