[petsc-users] Solving tridiagonal hermitian generalized eigenvalue problem with SLEPC

[Jed Brown]

Toon Weyens <tweyens at fis.uc3m.es> writes:

> Okay I reread again your answers and it seems that I missed the fact that I
> do not need shift invert to find the EV with the largest real part? 

Correct, inversion is way more expensive and used to find internal
eigenvalues.

> Then the "trick" of ex. 13 does not apply (they look for something
> close to 0).  So what could I do to avoid the LU?

Is your matrix B singular?  What are its boundary conditions?  You have
to solve with B for the generalized eigenvalue problem.  That could be
done iteratively, but a direct solve makes sense for a tridiagonal
system and the zero pivot likely indicates a deeper issue with the
formulation that won't vanish simply by avoiding LU.
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