Hi, I am dealing with a 'quasi upper triangular matrix', that is mentioned in the book 'Matrix Computations' by Golub & Van Loan. However, neither in the book itself, or anywhere on the internet, am I able to find a formal definition of a 'quasi upper triangular matrix'. I have a rough idea what this is.. an upper triangular matrix, with the odd non-zero element(s), somewhere along it's sub-diagonal. But I need an actual formal definition. Anyone furnish me with one please?