* each degree of freedom, depending for example on the local neighborhood of
* the respective node on a computational grid.
*
- * The right hand side is built up in the same way, i.e. by copying all entries
- * that coupled with the one under present consideration, but it is augmented
- * by all degrees of freedom coupling with the degrees from the set described
- * above (i.e. the DoFs coupling second order to the present one).
+ * The right hand side is built up in the same way, i.e. by copying
+ * all entries that coupled with the one under present consideration,
+ * but it is augmented by all degrees of freedom coupling with the
+ * degrees from the set described above (i.e. the DoFs coupling second
+ * order to the present one). The reason for this is, that the local
+ * problems to be solved shall have Dirichlet boundary conditions on
+ * the second order coupling DoFs, so we have to take them into
+ * account but eliminate them before actually solving; this
+ * elimination is done by the modification of the right hand side, and
+ * in the end these degrees of freedom do not occur in the matrix and
+ * solution vector any more at all.
*
* This local system is solved and the values are updated into the
* destination vector.
* whether this might pose some problems in the inversion of the local matrices.
* Maybe someone would like to check this.
*
- * @author Guido Kanschat, 1999
- */
+ * @author Guido Kanschat, documentation mostly by Wolfgang Bangerth; 1999 */
template<typename number>
class SparseVanka
{