CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

mahdavi wrote:
> hi,
> thanks for your help ,I write follow code and error again occur,please help
> me ,thanks
> code is:
> ////////////////////////////////////////////
> #include <CGAL/Lazy_exact_nt.h>
> typedef CGAL::Lazy_exact_nt<CGAL::Gmpq>  NT;
> K::Sphere_3 k1(Point_3(0,0,0),4.00003725);
>  NT l1=sqrt(k1.squared_radius());
Sqrt is not defined on such a number type.

If you want to manipulate exactly those kind of numbers you have to use 
algebraic numbers of degree 2 (otherwise use double and CGAL::to_double).
This would be equivalent to write:
CGAL::Root_of_traits_2<NT>::Root_of_2 
l1=CGAL::make_root_of_2(0,1,k1.squared_radius());

Please have a look at:
http://www.cgal.org/Manual/last/doc_html/cgal_manual/NumberTypeSupport_ref/Class_Root_of_traits_2.html#Cross_link_anchor_115
http://www.cgal.org/Manual/last/doc_html/cgal_manual/NumberTypeSupport_ref/Concept_RootOf_2.html#Cross_link_anchor_113
http://www.cgal.org/Manual/last/doc_html/cgal_manual/NumberTypeSupport_ref/Function_make_root_of_2.html#Cross_link_anchor_116

S.

> ////////////////////////////////////////////////////////////
> error :
> cannot convert from 'CGAL::Null_functor::result_type' to
> 'CGAL::Lazy_exact_nt<ET_>'
> /////////////////////////////////////////////////////