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Driver `dndrv3` uses the regular inverse mode to solve the
generalized eigenvalue problem. This mode should be used
if is symmetric and positive definite but it is not
possible to factor into a Cholesky factorization or
if there is reason to think that is ill-conditioned.
To use `dndrv3` the user must supply the action of
The action of is typically done with an iterative
solver such as pre-conditioned conjugate gradient.
If can be factored
then direct conversion to a standard problem is recommended.
This driver is appropriate for `which = 'LM','LR', 'SR','LI','SI'`
settings. If interior eigenvalues are sought then driver `dndrv4`
is probably more appropriate. If convergence is slower than
desired then one of the shift-invert modes described below should be used.

*Chao Yang*

*11/7/1997*