nodal activity assignments --
example:
(a) (b) (c)
31 0 1 0
(a) node # -- global index number of node
(b) gen order -- used to specify a range of nodes; generally just
leave it 0 unless doing something special.
(c) bc codes -- there are ndof entries (two in this example); tells whether each d.o.f. for this node is fixed or free; 0 =
fixed, 1 = free.
End nodal activity block with two zeros.
The followong figure illustrates fixed and free degrees of freedom
in this example. Unlabelled nodes are free (1 1), nodes with a blue
cross are fixed (0 0), and nodes with arrows are free in the x direction only
(1 0).
