[PPL-devel] Polyhedra with non-integral coefficients

[Alet Roux]

Dear Pat,

Thank you for the prompt response!

> Yes, the coefficients of constraints and generators have to be integers
> (mpz_class in the default configuration). However, the PPL implements a
> domain of convex _rational_ polyhedra. The restriction to integer
> coefficients is just for the representation and input/output. We can do
> this since any constraint having rational coefficients can be normalized
> so as to have integer coefficients. For generators, the same is achieved
> by including an integer divisor, (which by default is 1, but not
> necessarily so).
Thank you for pointing this out - I missed the presence of integer 
divisors. With the divisors, the library completely serves our needs.

> I see from your email that you already have written your own algorithms
> for intersection and convex-hull. These as well as union are operations
> provided by the PPL. Documentation for these is in the PPL; but if you
> miss the exact information needed to make full use of the PPL, you
> should not hesitate to ask.
Apologies, I was unclear: in fact I should have said we have algorithms 
that *make use* of intersection, convex-hull, etc. These algorithms are 
exactly the reason why I am interested in using the PPL.

Best wishes

Alet

-- 
Dr. Alet Roux
Lecturer in Mathematical Finance
Course Director of MSc in Mathematical Finance (campus based)
University of York, Heslington, York, YO10 5DD, United Kingdom
Tel: +44 (0)1904 324596
Fax: +44 (0)1904 323071
Email Disclaimer: http://www.york.ac.uk/docs/disclaimer/email.htm