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<title>Carpet Version 3</title>
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<h1>Carpet Version 3</h1>
<p>The release branch for Carpet Version 3 was created on
September 26, 2006. Version 3 has several major improvements over
version 2; all users of version 2 should consider updating.</p>
<p>Special thanks appertain to Luca Baiotti, Ian Hawke, Christian
D. Ott, Thomas Radke, Jonathan Thornburg, and Steve White for
their contributions.</p>
<p>Here is a list of the major changes:</p>
<h3>Grid hierarchy</h3>
<ul>
<li>Carpet has improved support for dynamic regridding. Thorn
CarpetRegrid can automatically coalesce overlapping regions,
which simplfies specifying refined regions. A new Cactus
schedule bin <b>preregrid</b> was introduced where thorns can
schedule routines that decide on a new grid structure.</li>
<li>It is not necessary any more to allocate all storage for all
variables at all times, i.e., it is now reasonably possible to
honour the <b>STORAGE</b> statements in the schedule. This is
done by the parameter
setting <b>Carpet::enable_all_storage = no</b>, and
it can unsurprisingly reduce the memory requirements
considerably. This is not yet the default setting.</li>
<li>Carpet checks whether the grid hierarchy is properly nested.
This is only an advice, not a requirement, since a not
properly nested grid hierarchy is technically still well
defined. It is sometimes surprising how many grid points per
level are required for proper nesting.</li>
<li>Checkpointing stores the grid hierarchy, so that it can be
automatically faithfully recovered. This requires the
parameter
settings <b>Carpet::regrid_during_recovery = no</b>
and <b>CarpetIOHDF5::use_grid_structure_from_checkpoint = yes</b>.
This is not yet the default setting.</li>
</ul>
<h3>Performance</h3>
<ul>
<li>Carpet scales better on multiple processors.</li>
<li>Several of Carpet's internal administrative calculations are
faster</li>
<li>Carpet has timing and memory statistics, which help users
determine on what parts of a simulation the time is spent</li>
</ul>
<h3>I/O</h3>
<ul>
<li>A new thorn CarpetIOBasic replaces the old IOBasic,
providing more convenient screen output. It performs global
reductions over the whole grid hierarchy instead of one
reduction per refinement level.</li>
<li>CarpetIOASCII produces one-dimensional output along the
diagonal.</li>
<li>Each output file is annotated with a unique build id and a
unique simulation id, so that files can be associated with the
run and source tree that produced them. This requires thorn
Formaline to be active.</li>
</ul>
<h3>Interpolation</h3>
<ul>
<li>CarpetLib provides WENO (Weighted Essentially
Non-Oscillatory) prolongation operators for hydrodynamics
simulations. CarpetLib had already support for TVD and ENO
operators, in addition to the standard Lagrange
operators.</li>
<li>CarpetInterp supports using non-standard (but still uniform)
coordinate systems, allowing interpolating in grid arrays.
Several serious errors in CarpetInterp were corrected.</li>
</ul>
<h3>Multi-patch and multi-model</h3>
<ul>
<li>Checkpointing and recovery with multiple grid patches was
corrected.</li>
<li>Different grid patches can have different (local) grid
spacings and different numbers of grid points.</li>
<li>There is initial support for multi-model simulations. These
are essentially independent simulations which are coupled only
e.g. through a boundary condition between two disjoint domains
containing different physical systems.</li>
</ul>
<h3>Documentation and utilities</h3>
<ul>
<li>Carpet's documentation was improved. In particular, the
schedule skeleton is now documented, describing which schedule
bins and which other actions occur in what order.</li>
<li>A variety of utilities for post-processing Carpet output
were added or improved, e.g. for convertion Carpet ASCII
output to the ygraph format, or for extracting certain pieces
of HDF5 files.</li>
</ul>
<h3>Smallish things</h3>
<ul>
<li>Many small errors were corrected</li>
<li>Many small features were added</li>
<li>Some error messages were improved</li>
<li>Many superfluous warning messages were removed</li>
<!-- Shameless self-advertising -->
<li>Carpet is now used by eleven relativity groups in the world.</li>
<!-- and it was the base for 15 scientific publications and at
least 2 PhD theses -->
<li>I'm looking for someone to make these web pages look
nicer.</li>
</ul>
<hr />
<p>Go back to the <a href=".">Carpet home page</a>.</p>
<hr />
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<address><a href="mailto:schnetter@cct.lsu.edu">Erik Schnetter</a></address>
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