Once an appropriate driver has been selected, it is necessary
to construct the action of the linear operator `OP` and matrix `B`
associated with that driver. Eigenvalues of `OP` are
computed by the computational routine `dsaupd`. These
eigenvalues are converted to those of or by the
post-processing routine `dseupd`. The Lanczos vectors generated
by `dsaupd` are orthogonal with respect to the (semi-) inner product
defined by `B`. It is imperative that the operations
and be computed as prescribed for the selected driver.
Table A.2 summarizes the operators `OP` and `B` required
for each driver.

Because of the reverse communication interface in 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.