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For each algorithm we have
distinguished between different ways of running the algorithm:
- ``Dir''
- is direct application, where we multiply with and solve with .
- ``SI''
- is shift and invert, which solves systems
for
and multiplies with . This gives
the ability to compute a wider choice of eigenvalues in fewer iterations.
- ``Prec''
- means application with a preconditioner, for instance,
a sparse approximate factorization. This needs
less space than shift and invert, but most often it also needs a larger number of matrix-vector multiplies.
Susan Blackford
2000-11-20