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 ofis 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.