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.