[Haskell-cafe] fast graph algorithms without object identities
alfonso.acosta at gmail.com
Fri Feb 1 09:41:10 EST 2008
You'd probably be interested to read
On Jan 31, 2008 9:56 PM, Jan-Willem Maessen <jmaessen at alum.mit.edu> wrote:
> On Jan 31, 2008, at 5:39 AM, Henning Thielemann wrote:
> > It seems that algorithms on graphs can be implemented particularly
> > efficient in low-level languages with pointers and in-place updates.
> > E.g.
> > topological sort needs only linear time, provided that dereferencing
> > pointers requires constant time. I could simulate pointer
> > dereferencings
> > and pointer updates by Map yielding linear logarithmic time for
> > topological sort. I wonder if it is possible to write a linear time
> > topological sort using lazy evaluation, since the runtime system of
> > Haskell implementations is a graph processor based on pointers.
> If so, I'd love to see this written up; I think it may be publishable
> if it isn't published already.
> Note that even using ST techniques can take more than linear time,
> given an arbitrary purely-functionally-defined graph as input. We
> can't (eg) assume that each node contains a reference, or that they
> are densely numbered, so we end up having to look them up in some
> fashion (though using a hash table can be reasonably quick if we
> uniquely number nodes).
> -Jan-Willem Maessen
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