Baruch and Bar Itzhack developed an alternative stiffness matrix update based on an optimal orthogonalization of the test mode shapes. The stiffness matrix perturbation using their method is:
(2.9.3-1)
where:
- Orthogonalized test
mode shapes
- Diagonal matrix
of test eigenvalues
The Baruch and Bar Itzhack perturbation can also be calculated using the unorthogonalized mode shapes, but it is not exact in that case. It is always symmetric, and while it is not minimum rank the perturbation terms are typically smaller than those calculated using the MRPT method. TAMKIT calculates either stiffness matrix perturbation using reduced matrices or the MRPT perturbation only using dynamically expanded test mode shapes.