An MP_Constraint represents a multiple point constraint in the
domain. A multiple point constraint imposes a relationship between the
displacement for certain dof at two nodes in the model, typically called
the retained node and the constrained node: U_c = C_{cr} U_r
An MP_Constraint is responsible for providing information on the
relationship between the dof, this is in the form of a constraint
Matrix, C_{cr}, and two ID objects, retainedID and
constrainedID indicating the dof's at the nodes
represented by C_{cr}. For example, for the following constraint
imposing a relationship between the displacements at node 1, the
constrained node, with the displacements at node 2, the retained
node in a problem where the x,y,z components are identified as the
0,1,2 degrees-of-freedom:
u_{1,x} = 2 u_{2,x} + u_{2,z}
u_{1,y} = 3 u_{2,z}
the constraint matrix is:
C_{cr} =
\left[
\begin{array}{cc}
2 & 1
virtual void setDomain(