[PPL-devel] Re: Horrible bug? [Was: Re: Compiling PPL under Cygwin?]

[Roberto Bagnara]

Goran Frehse wrote:
 > I had a feeling that you might be interested in the bug, but it only
 > occurred in the process of one specific example after many thousands of
 > iterations. I was not able to isolate the source, and creating the same
 > polyhedron by adding the constraints one by one resulted in the correct
 > empty polyhedron.

Dear Goran,

yes, we would be more than interested in the phenomenon you observed.

 > Once I'm past my current workload, I'll be happy to include your test
 > and see if I can find any strange things happening.

Thanks!

 > I minimized the polyhedron using "mypoly.minimized_constraints()".
 > Afterwards "mypoly" would be the proper solution.
 > This I found strange, since minimized_constraints() is declared "const",
 > so shouldn't it leave mypoly unchanged?

It leaves its "essence" unchanged, which means that `mypoly' would
continue to be a representation of exactly the same polyhedron.  But
it may be a different representation.

 > Is there any reason against using the minimizing versions?

Not at all.

 > Like I said,
 > it speeded things up for me by about 50%, as far as I can remember, even
 > though the polyhedra mostly were only generated once, checked for
 > intersection, and then forgotten. The speedup should be even greater
 > when the polyhedra are used several times for computations.

That is exactly the point in having the minimizing versions available:
their careful use (where "careful" here is a highly application-dependent)
can result in significant speedups.
Cheers,

     Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it