<html>#2647: incorrect WENO coefficient in GRHydro WENO reconstruction code
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<tr><td style='text-align:right'> Reporter:</td><td>Roland Haas</td></tr>
<tr><td style='text-align:right'> Status:</td><td>new</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>major</td></tr>
<tr><td style='text-align:right'>Component:</td><td>EinsteinToolkit thorn</td></tr>
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<p>The GRHydro WENO reconstruction code selected by <code>GRHydro::recon_method = "weno"</code> employs incorrect values for the <code>weno_coeffs</code> array that is constructed from the WENO $omega_r$ values. </p>
<p>The current values are in fact WENO interpolation instead of WENO reconstruction.</p>
<p>Pull request</p>
<p><a data-is-external-link="true" href="https://bitbucket.org/einsteintoolkit/einsteinevolve/pull-requests/17/rhaas-wenocoeffsfix" rel="nofollow">https://bitbucket.org/einsteintoolkit/einsteinevolve/pull-requests/17/rhaas-wenocoeffsfix</a></p>
<p>corrects the coefficients, re-computing them from the original publication used to implement the code (“WHAM paper”, <a data-is-external-link="true" href="https://arxiv.org/abs/0704.2608" rel="nofollow">https://arxiv.org/abs/0704.2608</a>) and updates the test data as well.</p>
<p>The attached stand-alone test (extracted code from GRHydro) demonstrates the issue and shows that only WENO-Z and WHAM’s WENO do show the WENO property of exactly reconstructing smooth data of low order polynomials (2nd order in the test, but should be up to 5th order). It also shows that WENO as implemented by GRHydro is actually WENO interpolation.</p>
<p>This effectively reduces WENO to a 2nd order accurate scheme similar to a basic tvd scheme I would guess.</p>
<p><table><tr><td>attachment:</td><td><a href="https://api.bitbucket.org/2.0/repositories/einsteintoolkit/tickets/issues/2647/attachments/weno.cc">weno.cc</a></td></tr>
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<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/2647/incorrect-weno-coefficient-in-grhydro-weno'>https://bitbucket.org/einsteintoolkit/tickets/issues/2647/incorrect-weno-coefficient-in-grhydro-weno</a></p>
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