** Next:** Generalized Eigenvalue Problem
** Up:** Selecting a Symmetric Driver
** Previous:** Standard Mode

Driver `dsdrv2` uses the shift-invert mode to find
eigenvalues closest to a shift . This is often used
to compute interior eigenvalues or clustered extremal eigenvalues.
For a discussion of shift-invert mode, see 3.2 in
Chapter 3. To use `dsdrv2`,
the user is required to supply the action of

This is typically accomplished by factoring the matrix
once before the iteration begins and then using this factorization
repeatedly to solve the sequence of linear systems that arise during
the calculation. The IRL iteration will find selected
eigenvalues of depending on the
setting of `which`.
To compute the eigenvalues of just to the right of , one should set `which = 'LA'` and for those just to the left
set `which = 'SA'`.
Eigenvalues closest to may
be obtained by setting `which = 'LM'`.
Eigenvalues to either side of may
be obtained by setting `which = 'BE'`.

*Chao Yang*

*11/7/1997*