fix solver doc

Polygon_mesh_processing/doc/Polygon_mesh_processing/NamedParameters.txt

@@ -18,11 +18,20 @@ and a `Kernel` in which constructions are performed and predicates evaluated.
 
 <li> `use_delaunay_triangulation`. A boolean. If `true`, use the Delaunay triangulation facet search space. Its default value is `true`.
 
-<li> `density_control_factor`. A floating scalar value which controls the density of the mesh generated by refinement. Its default value is `CGAL::sqrt(2)`.
+<li> `density_control_factor`. A floating scalar value which controls the density of the mesh generated by refinement, and larger values cause denser refinements. The density of vertices in the refined region is this factor times higher than before refinement.
+ Its default value is `CGAL::sqrt(2)`.
 
 <li> `fairing_continuity`. An unsigned integer which controls the tangential continuity of the output surface for fairing. The possible values are 0, 1 and 2, refering to the C^0, C^1 and C^2 continuity. The default value is 1.
 
-<li> `sparse_linear_solver`. An instance of the sparse linear solver used for fairing. It defaults to the Eigen solver ***
+<li> `sparse_linear_solver`. An instance of a class model of `SparseLinearAlgebraTraitsWithFactor_d`.
+ If \ref thirdpartyEigen "Eigen" 3.2 (or greater) is available and `CGAL_EIGEN3_ENABLED` is defined, then an overload of `Eigen_solver_traits` is provided as default value :\n
+\code
+CGAL::Eigen_solver_traits<
+Eigen::SparseLU<
+CGAL::Eigen_sparse_matrix<double>::EigenType,
+Eigen::COLAMDOrdering<int> >  >
+\endcode
+
 
 </ul>
 

Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/fair.h

@@ -60,17 +60,7 @@ namespace internal {
   Note that the structure is not altered in any way, only positions of the vertices get updated.
 
   Fairing might fail if fixed vertices, which are used as boundary conditions, do not suffice to solve constructed linear system.
-  The larger `continuity` gets, the more fixed vertices are required.
 
-
-  @tparam SparseLinearSolver a model of SparseLinearAlgebraTraitsWithFactor_d. If \ref thirdpartyEigen "Eigen" 3.2 (or greater) is available
-  and `CGAL_EIGEN3_ENABLED` is defined, then an overload of `Eigen_solver_traits` is provided as default parameter:\n
-   \code
-      CGAL::Eigen_solver_traits<
-          Eigen::SparseLU<
-             CGAL::Eigen_sparse_matrix<double>::EigenType,
-             Eigen::COLAMDOrdering<int> >  >
-  \endcode
   @tparam PolygonMesh a model of `FaceGraph`
   @tparam VertexRange a range of vertex descriptors of `PolygonMesh`, model of `SinglePassRange`
   @tparam NamedParameters a sequence of \ref namedparameters
@@ -82,7 +72,7 @@ namespace internal {
   \b Named \b parameters
   <ul>
   <li>\b vertex_point_map the property map with the points associated to the vertices of `pmesh`
-  <li>\b fairing_continuity tangential continuity of the output surface patch
+  <li>\b fairing_continuity tangential continuity of the output surface patch. The larger `fairing_continuity` gets, the more fixed vertices are required.
   <li>\b sparse_linear_solver an instance of the sparse linear solver used for fairing
   </ul>
 

Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/triangulate_hole.h

@@ -173,18 +173,6 @@ namespace Polygon_mesh_processing {
   \ingroup PkgPolygonMeshProcessing
   @brief triangulates, refines and fairs a hole in a polygon mesh.
 
-  If \ref thirdpartyEigen "Eigen" 3.2 (or greater) is available
-  and `CGAL_EIGEN3_ENABLED` is defined, an overload of this function is available
-  with `SparseLinearSolver` being:
-  \code
-  CGAL::Eigen_solver_traits<
-  Eigen::SparseLU<
-  CGAL::Eigen_sparse_matrix<double>::EigenType,
-  Eigen::COLAMDOrdering<int> >  >
-  \endcode
-
-
-  @tparam SparseLinearSolver a model of `SparseLinearAlgebraTraitsWithFactor_d`
   @tparam PolygonMesh a model of `MutableFaceGraph`
   @tparam FaceOutputIterator model of `OutputIterator`
       holding `boost::graph_traits<PolygonMesh>::%face_descriptor` for patch faces