Linear constraint equations provide a more general means of relating degree-of-freedom values than is possible with simple coupling. Constraint equations must have the form:

where U(I) is the degree of freedom of term (I), and N is the number of terms in the equation. The degree of freedom is in the nodal coordinate system. CEINTF, CERIG, and RBE3 correctly account for any rotated nodes in their generation of the constraint equations.