Hello, I have a question about how Abaqus performs the *SUBSTRUCTURE, GENERATE operation. The documentation (Abaqus-> Theory -> Procedures -> Substructuring and submodeling -> Substructuring and substructure analysis) provides the math to find the reduced stiffness matrix, but the math includes an inverse of the stiffness matrix corresponding to the eliminated degrees of freedom. In practice, this inverse would be very expensive, so I'm doubtful that Abaqus computes it this way.

Another paper ("Practical Reduction of Structural Eigenproblems") reports that the essential substructure quantities (the reduced stiffness matrix and transformation between eliminated and retained degrees of freedom) can be found via Gauss-Jordan elimination. I've attached a screenshot of the relevant text. Is Abaqus performing a similar operation? 

I appreciate your time in advance.