* matter if you use a continuous
* or discontinuous version of
* the finite element.
+ *
+ * It is worth noting that there
+ * are a few confusing cases of
+ * this function. The first one
+ * is that it really only makes
+ * sense to project onto a finite
+ * element that has at most as
+ * many degrees of freedom per
+ * cell as there are quadrature
+ * points; the projection of N
+ * quadrature point data into a
+ * space with M>N unknowns is
+ * well-defined, but often yields
+ * funny and non-intuitive
+ * results. Secondly, one would
+ * think that if the quadrature
+ * point data is defined in the
+ * support points of the finite
+ * element, i.e. the quadrature
+ * points of
+ * <tt>ths_quadrature</tt> equal
+ * <tt>fe.get_unit_support_points()</tt>,
+ * then the projection should be
+ * the identity, i.e. each degree
+ * of freedom of the finite
+ * element equals the value of
+ * the given data in the support
+ * point of the corresponding
+ * shape function. However, this
+ * is not generally the case:
+ * while the matrix <tt>Q</tt> in
+ * that case is the identity
+ * matrix, the mass matrix
+ * <tt>M</tt> is not equal to the
+ * identity matrix, except for
+ * the special case that the
+ * quadrature formula
+ * <tt>lhs_quadrature</tt> also
+ * has its quadrature points in
+ * the support points of the
+ * finite element.
*/
template <int dim>
static