[PPL-devel] Re: PPL and parameters

[Roberto Bagnara]

Sven Verdoolaege wrote:
 > On Fri, Feb 06, 2004 at 07:48:42PM +0100, Roberto Bagnara wrote:
 >
 >>I am not sure I understand what you mean.  The current version of the
 >>PPL is also based on GMP (even though we have a development branch to
 >>implement support for native integers and other kinds of coefficients, see
 >>http://www.cs.unipr.it/pipermail/ppl-devel/2004-February/004115.html).
 >
 >
 > Interesting.  Have you performed any run time comparison ?
 > A GMP-PolyLib is a lot slower than an integer-Polylib.

Not yet.

 >>>A quick glance at the documentation suggests that PPL only
 >>>supports what Omega would call "set variables".
 >>>Are there any plans for supporting parameters and/or
 >>>existential variables ?
 >>
 >>What do you mean by "existential variables"?
 >
 >
 > The usual.  Existentially quantified variables.
 > E.g., { x : \exists a : 4 a + 1 <= x <= 4a + 2 }

The variable `a' is bound to be an integer, right?
Am I correct if I say that you are interested in systems
of what, IIRC, Masdupuy calls "trapezoid congruences",
i.e., things of the form

     a1*x1 + ... an*xn in [l, u] (mod k),

which should mean

     mod(a1*x1 + ... an*xn, k) belongs to the interval [l, u],

where a1, ..., an, l, u are rational numbers and k is a natural?
You set above should then correspond to

     x \in [1, 2] (mod 4).

These are in our list of the things we want to support.

@PhDThesis{Masdupuy93th,
   Author = "F. Masdupuy",
   Title = "Array Indices Relational Semantic Analysis
            Using Rational Cosets and Trapezoids",
   Type = "{Th\`ese d'informatique}",
   School = "\'Ecole Polytechnique",
   Address = "Palaiseau, France",
   Month = dec,
   Year = 1993
}

 >>I think we will support parameterized polyhedra in the future.
 >>But this is something that will not happen tomorrow.
 >
 >
 > I'll see if I can get a student on it next year.
 > I'm not holding my breath, though.
 > Apparently, the word "polytope" scares people off.

Tell them that, for whoever does a nice job on the subject and
is willing to give a seminar, there is a free trip to Parma to
be won :-)
All the best,

     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