An unsymmetric
tridiagonal matrix of order `n` is stored in
three one-dimensional arrays, one of length `n` containing the
diagonal elements, and two of length `n` - 1 containing the
subdiagonal and superdiagonal elements in elements 1 : `n` - 1.

A symmetric tridiagonal or
bidiagonal matrix is stored in
two one-dimensional arrays, one of length `n` containing the
diagonal elements, and one of length `n` containing the
off-diagonal elements. (EISPACK routines store the off-diagonal
elements in elements 2 : `n` of a vector of length `n`.)

Tue Nov 29 14:03:33 EST 1994