> On 18 Jan 2015, at 17:49, Jose E. Roman <[email protected]> wrote: > > STSetShift() is a remnant of the old interface, before the target was > introduced. The intended usage for the application is to use a target (set > with EPSSetTarget) in combination with EPS_TARGET_XXX. STSetShift() could be > used for the case that the target coincides with an eigenvalue (to avoid > solving a singular system). > > When you set the target in shift-and-invert, two things happen: (1) the shift > is set to the target and (2) eigenvalue approximations are sorted with > respect to the target. The latter may be important for convergence. So it is > recommended to set the target, not the shift. > > For STSHIFT, the shift is irrelevant because Krylov subspaces are shift > invariant. But non-Krylov solvers may depend on the shift. > > For a GHEP, if you know where your eigenvalues are, use shift-and-invert with > a target and EPS_TARGET_XXX.
Thanks for your detailed explanation! I will give it a try the way you suggested. Kind regards, Denis.
