welcome any comments on how to solve block tridiagonal linear system, or where can I get free code about this problem? thanks in advance yours zl

(1). Check the book by John C. Tannehil et al, "Computational Fluid Mechanics and Heat Transfer". I remember seeing something like that in the Appendix sections of the book, old version. (2). Don't have time to do checking. Good luck.

Try Netlib. You may find tridiagonal but pentadiagonal solvers as well. I also don´t have much time to give you a more precise answer

Giannis