<html>#2272: GRHydro C2P inconsistency with and without magnetic field evolution
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<tr><td style='text-align:right'> Reporter:</td><td>Lorenzo Sala</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>ET_2018_09</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>Comment (by Roland Haas):</p>
<p>I had a chat with <span class="ap-mention" data-atlassian-id="557058:69c77ee3-2990-4bbe-8f32-df58269ccd1e">@pmoesta</span> who is using GRHydro for MHD simulations. Philipp had a look at your parfile and pointed out two issues that I had missed:</p>
<ol>
<li>you need to set <code>GRHydro::transport_constraints = yes</code> otherwise the default is a free B field evolution which is unstable and quite likely very much untested. </li>
<li>you should set <code>HydroBase::initial_Bvec = "zero"</code> rather than <code>None</code> (unless some code of your own actually sets <code>Bvec</code> to zero). Otherwise <code>Bvec</code> is not initialized and would retain the poison value that <code>Carpet</code> sets it two when allocating memory for it (or even worse it would be left unitalized which could be any random value if poisoning is not used).</li>
</ol>
<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/2272/grhydro-c2p-inconsistency-with-and-without'>https://bitbucket.org/einsteintoolkit/tickets/issues/2272/grhydro-c2p-inconsistency-with-and-without</a></p>
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