[petsc-dev] quasi-newton approximations

[Munson, Todd]

One of the common concepts for TAO and SNES is the quasi-Newton approximations.
SNES seems to only use them in SNESQN (for non-symmetric matrices) and TAO uses
them in TAOLMVM and TAOBLMVM (for symmetric matrices).  TOA also allows them to
be used as a preconditioner for the Hessian-based line-search and trust-region
methods.

Should we consider extracting some common class for these approximations and 
the associated operations or just leave them as separate things?

Todd.