Once a driver is chosen, the next step is to identify `OP` and `B`
associated with that driver. Eigenvalues of `OP` are computed by the
computational routine `dnaupd`. These eigenvalues are converted
to those of or in the post-processing routine
`dseupd`. The Arnoldi vectors generated by `dnaupd` are
`B`-orthonormal. It is very important to construct the matrix
vector operations

Because of the reverse communication interface of ARPACK, the construction of is left completely to the user. This means that the user is free to choose any convenient data structure for the matrix representation. If the matrix is not available, the user is free to express the action of the matrix on a vector through a subroutine call or a code segment.