<html>#2471: Carpet: npoints[d] <= max issue
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<tr><td style='text-align:right'> Reporter:</td><td>Lunan Sun</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>Carpet</td></tr>
</table>
<p>Comment (by Erik Schnetter):</p>
<p>Lunan</p>
<p>Cactus (and Carpet) use <code>int</code> to access arrays. This means that the maximum number of grids points is limited to be about 2e9.</p>
<p>Parts of Carpet have been extended to use 64-bit integers. I think that many parts of Carpet will work correctly as long as the process-local grid size is less than 2e9. Unfortunately, there is no good way to flag integer overflow errors in C or C++, and it is thus difficult to debug this.</p>
<p>You might get lucky if you simply disable this check. There are other checks for process-local grid sizes that would trigger if things go wrong. If you don’t get lucky, then there will be weird errors. I assume that most such errors will affect “unimportant” things such as calculating the average over a full grid function, or estimating the current progress rate in terms of number of grid points per second that are evolved.</p>
<p>If you are familiar with C/C++ and integer overflow, then this is worth an attempt. You can also build a version of your code with compiler options that check for signed integer overflow to see whether this triggers an error. I’ll be happy to assist if needed.</p>
<p>If you are not familiar with this, then I would not advise trying this, because the C/C++ standards are not exactly user friendly. In this case, using a smaller domain is the only way to go. You might try using mesh refinement, which generally leads to smaller numbers of grid points.</p>
<p>We’re currently working on a new driver “CarpetX”. We should make sure there are no respective limitations there.</p>
<p>-erik</p>
<p>--<br/>
Ticket URL: <a href='https://bitbucket.org/einsteintoolkit/tickets/issues/2471/carpet-npoints-d-max-issue'>https://bitbucket.org/einsteintoolkit/tickets/issues/2471/carpet-npoints-d-max-issue</a></p>
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