s(plates)

               The elements

                  plates(1,i)
                  plates(2,i)
                  plates(3,i)

               are, respectively, the indices of the vertices
               comprising the ith plate.

               Note that the order of the vertices of a plate is
               significant: the vertices must be ordered in the
               positive (counterclockwise) sense with respect to
               the outward normal direction associated with the
               plat