Changes (by Roland Haas):

assignee:	Roland Haas (was )
responsible:	[] (was )

AEILocalInterp by default will off-centre the interpolation stencil if there are insufficient points to perform the interpolation. In a parallel setting, this could happen due to there being insufficient ghost points for the interpolator chosen. The off-centering leads to an interpolation error which is of the correct order but larger than for a centered stencil. More importantly, it leads to different results on different numbers of processes. This violates a basic design principle of Cactus, and the expectation of users, that changing the number of processors should not change the results of a simulation.

I propose that instead of silently off-centering the stencil, AEILocalInterp should abort with an error indicating that there are insufficient ghost-zones. The interpolator options corresponding to this are:

boundary_off_centering_tolerance={0.0 0.0 0.0 0.0 0.0 0.0} boundary_extrapolation_tolerance={0.0 0.0 0.0 0.0 0.0 0.0}

Keyword: AEILocalInterp

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/181/aeilocalinterp-should-not-off-centre-the