<html>#2373: kasner example from ET paper cannot be reproduced
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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>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>major</td></tr>
<tr><td style='text-align:right'>Component:</td><td>EinsteinToolkit thorn</td></tr>
</table>
<p>Comment (by Roland Haas):</p>
<p>Running the <a data-is-external-link="true" href="https://bitbucket.org/einsteintoolkit/einsteinexamples/raw/1f7de206cfbb1f5d48eb1bd5cef0e01ccacb1997/par/arXiv-1111.3344/cosmology/kasner.par" rel="nofollow">kasner.par</a> file from einsteeinexamples with a number of previous ET releases:</p>
<ul>
<li>ET_2019_03 "Proca"</li>
<li>ET_2013_05 "Gauss"</li>
<li>ET_2011_10 "Maxwell": aborts with NaN found in step 0</li>
<li>ET_2011_05 "Curie"</li>
</ul>
<p>shows the same behaviour for all of them, namely exponential growth i n gxx.</p>
<p><img alt="" src="https://bitbucket.org/repo/8zBLME5/images/4108858268-kasner.png" />
Note that Curie is the release before the parfile shows up and also the release before the ET paper showing the Kasner example, Maxwell is the release just after and the first one to contain the parfile.</p>
<p>This turns out to be due to the fact that <code>ML_BSSN</code>, while it extends <code>ADMBASE::lapse_evolution_method</code> actually ignores that parameter and evolves the lapse with its default gauge condition. This is despite the parfile setting:</p>
<div class="codehilite language-c++"><pre><span></span><span class="n">ADMBase</span><span class="o">::</span><span class="n">lapse_evolution_method</span> <span class="o">=</span> <span class="s">"static"</span>
<span class="n">ADMBase</span><span class="o">::</span><span class="n">shift_evolution_method</span> <span class="o">=</span> <span class="s">"static"</span>
<span class="n">ADMBase</span><span class="o">::</span><span class="n">dtlapse_evolution_method</span> <span class="o">=</span> <span class="s">"static"</span>
<span class="n">ADMBase</span><span class="o">::</span><span class="n">dtshift_evolution_method</span> <span class="o">=</span> <span class="s">"static"</span>
</pre></div>
<p>It can be fixed by choosing gauge evolution parameters such that all RHS for the gauge quantities are zero:</p>
<div class="codehilite language-c++"><pre><span></span><span class="cp"># ML_BSSN ignores gaug
<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/2373/kasner-example-from-et-paper-cannot-be'>https://bitbucket.org/einsteintoolkit/tickets/issues/2373/kasner-example-from-et-paper-cannot-be</a></p>
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