[m-rev.] for review: Implement simple_tc algorithm.

[Peter Wang]

On Wed, 18 Jan 2023 15:36:57 +1100 Julien Fischer <jfischer at opturion.com> wrote:
> 
> On Tue, 17 Jan 2023, Peter Wang wrote:
> 
> > Implement transitive closure using the simple_tc algorithm from
> > Esko Nuutila's doctoral thesis.
> >
> > Based on some runs on randomly generated graphs of 100 to 3000 vertices
> > (see tests/hard_coded/digraph_tc.m), the simple_tc implementation was
> > about 1.75 to 2.8 times as fast as the old implementation on my machine.
> > (It would be many times faster if we did not have to maintain the
> > predecessor maps required by the digraph representation.)
> >
> > library/digraph.m:
> >    Rename digraph.tc and digraph.rtc to digraph.old_tc and
> >    digraph.old_rtc. They are kept around for benchmarking,
> >    and will be deleted soon.
> 
> I think we should rename them to transitive_closure and
> reflexive_transitive_closure (even the latter is a bit long).
> 

Hmm, I'm not sure it's worth changing.

> > +                % The successors and precessors of each vertex in the graph
> 
> predecessors.

Fixed, thanks.

Peter