Dear Roberto,

Thanks again for your clarification. I made a workaround by declaring a temporary variable for consys, and copy a consys to it and add the temp consys to the polyhedron. It works fine, and it looks like I missed another important point in the documentation. Yeah, I'm sure that the additional recycled_constraints interface would certainly be of much help. Before that, I would like that warning to be emphasized in a specific way like my case. Thanks.

Best wishes,

Hosung

Roberto Bagnara wrote:

Hosung Song wrote:

...

When I add constraint system to polyhedron by ppl_Polyhedron_add_constraings(poly, consys), it looks like consys is cleared to universe. Is this a right behavior? I naively thought the consys would be preserved. Is this related to the recycle issue between ordinary polyhedron instantiation and recycled instantiation? Thanks in advance.

Dear Hosung,

yes, ppl_Polyhedron_add_constraints(poly, consys) does modify consys in an unpredictable way. If you look at the user's manual, or in ppl_c.h in the include subdirectory of your installation prefix, or at the file ppl_c.h.in in the distribution, you will see something like

/*! \brief Adds the system of constraints \p cs to the system of constraints of \p ph.

\warning This function modifies the constraint system referenced by \p cs: upon return, no assumption can be made on its value. */ int ppl_Polyhedron_add_constraints(ppl_Polyhedron_t ph, ppl_ConSys_t cs);

Moreover, you should notice that the `cs' argument is of type `ppl_ConSys_t' and not `ppl_const_ConSys_t', so that it can be modified. The reason of this design choice is that often a constraint system is only built to be added to a polyhedron, after which serves no other purposes. By using its data structures, unnecessary memory allocations and deallocations are avoided. We should perhaps name the function differently and perhaps provide also the other behavior. How about

ppl_Polyhedron_add_recycled_constraints

for the current behavior and keeping

ppl_Polyhedron_add_constraints

for the version that does not modify the constraint system? Do you think this would help the users of the C interface? All the best,

Roberto