[Carpet] Carpet Status Report (2006-08-13)

[Erik Schnetter]

Carpet Status Report

One kind of error that is not easy to pinpoint are uninitialised grid  
functions.  It can be that only a few grid points on some refined  
regions may remain uninitialised, which makes this error appear to be  
almost non-deterministic.  One sign of such uninitialised grid points  
are e.g. nans which appear after some iterations.  We found recently  
that making Carpet initialise all grid functions with special values  
(e.g. nans) helps finding such errors.  This is called "poisoning"  
the grid functions.  Not only Carpet, but also CarpetLib can now  
poison newly allocated memory.  This can also be used to find errors  
in Carpet itself, e.g. for new prolongation operators.

In order to find out where a simulation spends its time, I have  
introduced two new sets of timers to Carpet.  One set is located in  
Carpet, and it measures in which part of the evolution steps the time  
is spent.  This complements Cactus's timers for the scheduling bins,  
as it also measures the time spent between scheduling bins, such as  
for restriction and I/O.  The second set is located in CarpetLib, and  
it keeps statistics about time spent in communication and other inter- 
grid transfer operations.  These timers can be activated via parameters.

I have generalised the way in which Carpet parallelises the grid  
hierarchy for multi-patch simulations.  Previously, each patch was  
parallelised independently.  That meant that each patch was  
distributed over all processors.  There is now a parameter  
Carpet::regrid_in_level_mode which parallelises the whole grid  
structure at the same time.  This means that e.g. six patches on six  
processors are distributed in a one-patch-per-processor fashion,  
which is more efficient.  This feature is new and not yet well tested.

Gian Mario Manca from the Università di Parma published a set of  
visualisation scripts for Matlab.  These scripts are available from  
the Carpet web site.

Gian Mario Manca and Jonathan Thornburg contributed pictures from  
their simulation results for the Carpet web site.

I removed the links to our own (meanwhile outdated) darcs binaries.   
The darcs web site has now a large selection of darcs binaries for  
many architectures.  The current version of darcs is 1.0.8 --  
consider updating.  Version 1.0.8 can make use of ssh's multiplex  
feature to increase its speed.  Versions 1.0.1 and older may not work  
any more with Carpet's repository.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>

My email is as private as my paper mail.  I therefore support encrypting
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