# Rigid Constraints

For a rigid constraint there are a set of constraint equations which respect the geometry of the constraint. So for a single constrained node the constraint equations are

where the terms are for a fixed and for a pinned rigid constraint.

Different terms in the matrix are dropped for reduced constraint types. The two most common special types are plane and plate constraints with equations

for an plane constraint. Similarly for and plane constraints.

for a plate constraint. Similarly for and plate constraints.