On Tue, 09 Nov 2004 21:50:57 +0100 Roberto Bagnara bagnara@cs.unipr.it wrote:
By the way, we (the PPL developers) are more and more curious about these Haskell bindings we have read about in some recent messages to the mailing list. It may come as a surprise to you, but we never saw them and we have not the slightest idea about how they look like. Can you give us a pointer?
The bindings are just Haskell library code that calls the PPL C interface functions. It also defines Haskell wrapper types for (pointers to) the PPL data objects. So effectively the Haskell interface in built on top of the C one.
Axel Simon wrote the basic Haskell interface code and I got it from him. He didn't made publicly available because the
Now the question I have is: what is the prefered way to ensure that a powerset is Omega-reduced, i.e. all its elements are maximal wrt the original partial order (in particular, removing bottom elements)? Polyhedra_PowerSet<C_Polyhedron> has a member function `omega_reduce()' that is suposed to do just this, but it is protected, so the compiler complains if I try to use in the C interface.
The interface for Polyhedra_Powerset is still experimental and we are still designing it. Since the release of PPL 0.6.1 we have been very busy doing other things (a good part of them PPL-related) and this part of the library has suffered a bit. It would be nice if we could take the occasion and work with you and Hosung towards improving and finishing this part of the work. This is especially important for us also in view of the new numerical abstractions we are about to add to the library: bounding boxes, bounded differences, octagons, grids, ... all of them can be used as arguments to the powerset construction.
So, let us start with your question. Premise number 1 is that I am not against providing `omega_reduce()' to the user of Polyhedra_Powerset. Premise number 2 is that I prefer to be extra-sure providing `omega_reduce()' to the user of Polyhedra_Powerset is the right thing to do. The obvious question I have to ask you is: why would you want to have access to `omega_reduce()? What is the effect you wish to obtain? Afterall, one may say that a Polyhedra_Powerset and its omega-reduced counterparts have the same semantics. (You can of course reply, and rightly so, "Why do you provide pairwise_reduce() then?" This only shows that the interface of powersets needs more work: perhaps [I am being provocative here] `pairwise_reduce()' should not be there.)
To make a parallel with a similar situation with the C_Polyhedron and NNC_Polyhedron classes, we do not provide a method `minimize()' to the user. We rather ask the user to declare what is wanted by calling `miminized_constraints()' or `minimized_generators()' and keep polyhedra minimization as an internal business the user needs not be concerned about. Up to now, this design choice has proved its value without showing any drawback.
To come back to the point you raise: is `omega_reduction()' precisely the things you want, or is it just something that either as a by product or in combination with other techniques will give you what you really want? In the latter case, what is that you really want? Do you want reduction to economize memory? To use less space when printing? Because you think subsequent operations will be cheaper?
The only solution I found is to use `pairwise_reduce()' instead. It seems to do what I want, but I am confused as to the reason for the protected function.
The method `pairwise_reduce()' does a different thing (please consult the documentation and complain if it does not provide enough information). And moreover, it is quite expensive.
Please excuse me (and please tell me!) if this is not the right forum to ask these questions.
This is _precisely_ the right forum for these questions. 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@cs.unipr.it _______________________________________________ PPL-devel mailing list PPL-devel@cs.unipr.it http://www.cs.unipr.it/mailman/listinfo/ppl-devel