CGAL users discussion list

[Bernd Gaertner <>]

Samuel Hornus wrote:
> To speed-up the computation, I would like to reuse the
> (already computed) Min_sphere from the left child of a node as a
> starting point in which to include the points of the right child,
> so as to obtain the bounding sphere of the node more quickly than from
> scratch.
>
> However, I get assertion failure in Min_sphere_of_spheres_d.h, line 253
> (trunk), because vector 'l' is already non empty.
>
>   template<class Traits>
>   inline void Min_sphere_of_spheres_d<Traits>::update() {
>     // set up the vector l containing pointers to the balls in S:
> HERE -->    CGAL_MINIBALL_ASSERT(l.size() == 0);
>     for (typename std::vector<Sphere>::const_iterator it = S.begin();
>          it != S.end(); ++it)
>       l.push_back(&(*it));
>     
>     // compute the miniball:
>     update(Algorithm());
>     is_up_to_date = true;
>   }
>
> Is it truly intentional in the sense that the computation is not
> restartable ? Or is it a over-zealous assertion ?

It is true that l needs to be empty; a restart does make use of the 
current optimal ball, but then goes through *all* inserted balls again 
for the update (this may be a waste in the first round of such an 
update, but it is unavoidable later). I think the fix is to insert the 
statement "l.clear();" right before the assertion. If you are successful 
with this, I will thoroughly test and submit a corresponding bug fix.

Best,
Bernd.