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If eigenvalues near a point are sought,
then one of the shift-invert drivers
`dndrv4`, `dndrv5` or `dndrv6` should be used. Driver
`dndrv4` can be used when the shift has a zero
imaginary
part. Otherwise, either `dndrv5` or `dndrv6`
should be used.
To use these drivers, one is required to supply the action of

When has a nonzero imaginary part, a complex
factorization routine or a complex iterative solver will be
required. In that case, the vector will in general be
a complex vector. However, only the real or imaginary part will
be passed into `dnaupd` and all arithmetic and data types
within the ARPACK routines will be real.
In any case, the IRAM will find selected
eigenvalues of depending on the
setting of `which`. The recommended setting for computing
eigenvalues of the pair () nearest to is `which = 'LM'`. However, other settings are not
precluded.

*Chao Yang*

*11/7/1997*