"Smith, Barry F." <[email protected]> writes: > Problem 2) Less catastrophic > > When cheb->kspest is set the "regular" Chebyshev is also run (after the > eigenvalues are estimated). I am pretty sure this is wrong because there is > no reason to run the Chebyshev when estimating the eigenvalues? The > eigenvalues are stored to be used later right?
The solve still needs to be applied because the Chebyshev smoother is intended as a linear operator. We use a noisy vector by default for estimation, but even if we were to use the smoother's RHS, the GMRES estimation provides a different correction than the associated Chebyshev. If we didn't care about nonlinear smoothing, we could use the GMRES correction instead. Or (with some math that could be worked out), we could recombine the first vectors of the GMRES Krylov space to provide the action of the Chebyshev smoother without needing to do more MatMults (but the quality of the eigenestimates would suffer unless the RHS happens to be noisy enough).
