An unsymmetric
tridiagonal matrix of order 
is stored in
three one-dimensional arrays, one of length containing the
diagonal elements, and two of length 
containing the
subdiagonal and superdiagonal elements in elements 
.
A symmetric tridiagonal or
bidiagonal matrix is stored in
two one-dimensional arrays, one of length containing the
diagonal elements, and one of length containing the
off-diagonal elements. (EISPACK routines store the off-diagonal
elements in elements 
of a vector of length .)