A Note on the Use of the Woodbury Formula To Solve Cyclic Block   Tri-Diagonal and Cyclic Block Penta-diagonal Linear Systems of Equations
  The article presents the theoretical background of the algorithms for solving cyclic block tridiagonal and cyclic block penta-diagonal systems of linear algebraic equations present in ref [1] and [2]. The theory is based on the Woodbury formula. 
Milan Batista, Abdel Rahman A. Ibrahim Karawia