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The reverse communication interface routine for all problem types
is __aupd. If the eigenvalue problem (3.2.1)
is a double precision non-symmetric one,
then the subroutine to use is dnaupd.
First the reverse communication loop structure will be described
and then the details and nuances of the problem set up will
We shall use the symbol OP for the
operator that is applied to vectors in the Arnoldi/Lanczos process
and will stand for the matrix to use in the
weighted inner product described previously.
For the shift-invert spectral transformation mode,
OP denotes and denotes . They will stand for different
matrices in each of the various modes.
The basic idea is to set up a loop that repeatedly calls __aupd.
On each return, one must
either apply OP or to a specified vector or exit the loop
depending upon the value returned in the reverse communication