pub fn two_node_dofs<NId: Copy, const N: usize>( i: NId, j: NId, ndof: usize, ) -> [DofRef<NId>; N]
DOFs of a two-node element laid out as [all of node i's slots, all of node j's slots]; N must equal 2 * ndof.
[all of node i's slots, all of node j's slots]
N
2 * ndof