CGAL users discussion list

["Laurent Rineau (CGAL/GeometryFactory)" <>]

On Monday, July 20, 2020 12:54:54 PM CEST Myirci wrote:
> Hi all,
> 
> I had been using CGAL actively for about 4 years ago and I have a project
> which I wanted to rebuild with the more recent version of CGAL 5.1 beta1. I
> have sorted out most of the compile errors but one simple thing caused lots
> of trouble which was working perfectly in the past but I cannot make it
> work right now. The error is related to a basic conversion from exact
> numbers such as CGAL::Gmpq, CGAL::Gmpz to double using the CGAL API such as
> CGAL::to_double() and CGAL::to_interval().
> 
> I wrote down a sample code (based on the example in the CGAL documentation
> for Algebraic Kernels)
[...]
> test.cpp:
> ----------------------------------------------------------------------------
> -----------------------------------
> 
> #include <CGAL/config.h>
> #include <CGAL/Algebraic_kernel_d_1.h>
> #include <CGAL/Gmpz.h>
> #include <vector>
> 
> typedef CGAL::Algebraic_kernel_d_1<CGAL::Gmpz>          AK;
> typedef AK::Coefficient                                 Coefficient;
> typedef AK::Polynomial_1                                Polynomial_1;
> typedef AK::Algebraic_real_1                            Algebraic_real_1;
> typedef AK::Bound                                       Bound;
> typedef std::pair<Bound,Bound>                          Interval;

Hi Myirci, to use to_interval with the GMP algebraic kernel, you need the 
MPFI library. Maybe on your older machine, MPFI was available.

If you do not have MPFI, you can use the CORE algebraic kernel, that way:

//--------------
#include <CGAL/config.h>
#include <CGAL/Algebraic_kernel_d_1.h>
#include <vector>

typedef CGAL::Algebraic_kernel_d_1<CORE::BigInt>          AK;
typedef AK::Coefficient                                 Coefficient;
typedef AK::Polynomial_1                                Polynomial_1;
typedef AK::Algebraic_real_1                            Algebraic_real_1;
typedef AK::Bound                                       Bound;
typedef std::pair<Bound,Bound>                          Interval;

int main()
{
    AK ak;
    AK::Construct_algebraic_real_1 construct_algebraic_real_1 = 
ak.construct_algebraic_real_1_object();
    Polynomial_1 x = CGAL::shift(AK::Polynomial_1(1),1); // the monomial x
    Algebraic_real_1 a = construct_algebraic_real_1(x*x-2,1); //  sqrt(2)

    std::cout << "sign of a is                 : " << CGAL::sign(a)      << 
"\n";
    std::cout << "double approximation of a is : " << CGAL::to_double(a) << 
"\n";
    std::cout << "double lower bound of a      : " << 
CGAL::to_interval(a).first  << "\n";
    std::cout << "double upper bound of a      : " << 
CGAL::to_interval(a).second << "\n";

    return 0;
}
//--------------


-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/