Hello Roberto,
thanks for the answer. So, once I converted my coefficients for constraints or point coordinates to integer (in an over-approximating fashion), the library ensures overapproximation in any case, right?
I already found the image and pre_image functions, but as they are not creating a new object (as far as I understood) but modify the current object, you cannot simply create a linear expression from each row and use the image function sequentially on your polyhedron.
Best regards, Stefan
On 23.11.2016 08:18, Roberto Bagnara wrote:
Hello Stefan.
On 11/22/2016 04:18 PM, Stefan Schupp wrote:
I am using PPL for my project which is related to verification. In this context I require my computations to be exact or, if that is not possible, to be over-approximating. From what I read in the documentation, PPL ensures such an over-approximation, which is nice. I am using C_Polyhedron as my data type and currently interested in using rational arithmetic (mpq_class) in combination with that. From what I see, you can use the mpz_class type for C_Polyhedron, but not mpq_class directly. Is there a way intended to overcome this problem?
More than a problem, this is a precise design decision motivated by efficiency reasons: conversion of coefficients of any kind to integer coefficients is left to the application. There are several examples in the library on how to do that: possibly the simplest one given by function normalize() in demos/ppl_lcdd/ppl_lcdd.cc .
In my current setup I use the double interface, but this requires conversion and most probably introduces rounding errors.
I am not sure I understand the first part of the sentence: which double interface are you using?
Furthermore a usage question: Is there an intended way on how to compute a linear transformation of a polyhedron with a matrix?
Look for the string "image" in the manual. Kind regards,
Roberto