<html>#181: AEILocalInterp should not off-centre the interpolation stencil by default
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<tr><td style='text-align:right'> Reporter:</td><td>Ian Hinder</td></tr>
<tr><td style='text-align:right'> Status:</td><td>open</td></tr>
<tr><td style='text-align:right'>Milestone:</td><td></td></tr>
<tr><td style='text-align:right'> Version:</td><td></td></tr>
<tr><td style='text-align:right'> Type:</td><td>bug</td></tr>
<tr><td style='text-align:right'> Priority:</td><td>minor</td></tr>
<tr><td style='text-align:right'>Component:</td><td>Cactus</td></tr>
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<p>Changes (by Roland Haas):</p>
<p><table>
<tr><td>assignee:</td><td>Roland Haas (was )</td></tr>
<tr><td>responsible:</td><td>[] (was )</td></tr>
</table></p>
<p>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.</p>
<p>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:</p>
<p>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}</p>
<p><strong>Keyword:</strong> AEILocalInterp</p>
<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/181/aeilocalinterp-should-not-off-centre-the'>https://bitbucket.org/einsteintoolkit/tickets/issues/181/aeilocalinterp-should-not-off-centre-the</a></p>
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