<html>#2754: Inconsistent definition of B in evolution thorns
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<tr><td style='text-align:right'> Reporter:</td><td>Samuel Cupp</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>minor</td></tr>
<tr><td style='text-align:right'>Component:</td><td>EinsteinToolkit thorn</td></tr>
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<p>GRHydro and IllinoisGRMHD use different definitions for several quantities. This is mostly fine, as IllinoisGRMHD converts <code>vel</code> to get its desired velocity variable. However, the magnetic variable <code>B</code> also differs between these two thorns by a factor of <code>sqrt(4pi)</code>. This means that GRHydro couldn't use, for example, initial data from the Seed_Magnetic_Fields thorns without rescaling them. Without an expectation for what <code>B</code> is, diagnostic thorns that need this variable will produce incorrect results if used with anything except for the evolution thorn they were designed for. Presumably, all the WVUThorns are using IlliniosGRMHD’s <code>B</code>, and GRHydro_InitData uses GRHydro’s <code>B</code>. Anything that isn't explicitly tied to an evolution thorn would be ambiguous. Is there a consensus on what <code>B</code> in HydroBase is expected to be?</p>
<p>Especially with the transition to CarpetX, having a single definition for B would likely help keep thorns mutually compatible.</p>
<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/2754/inconsistent-definition-of-b-in-evolution'>https://bitbucket.org/einsteintoolkit/tickets/issues/2754/inconsistent-definition-of-b-in-evolution</a></p>
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