## N

Comment: Each node is commonly rendered by a geometric point, but in fact it is simply an element of any set; so in a set of integers, each integer would be a node of a graph. A common synonym is vertex. When reactions and compounds are both nodes in the representation of a biochemical network, because there are two types of nodes, the network is said to be bipartite.

nonconforming finite elements A finite element space Vh is called nonconforming with respect to a function space V if Vh ⊂ V . Using Vh to discretize a variational problem over V amounts to a variational crime. However, it might be feasible, if Vh satisfies certain consistency conditions expressed in Strang’s second lemma.