Ghost points do not make sense since it is not clear how they should be set. This these arrays are not formed via a domain decomposition, there is no source process that would set them.
Another point to keep in mind is recovery on a different number of processes. If each process can have different data, then it does not make sense to recover these arrays on a different number of processes, since either information would be lost, or would have to be invented. -erik On Mar 9, 2014, at 22:01 , Roland Haas <[email protected]> wrote: > Signed PGP part > Hello all, > > while debugging some code using grid arrays with DISTRIB=CONSTANT I > noticed that Cactus's IOASCII output code outputs data from all > processes which differs from Carpet's CarpetIOASCII which outputs only > data from a single process. > > Carpet (and Cactus) seems to assume (see comments in line 89 in > CarpetIOHDF5/src/Output.cc) that "DISTRIB=CONSTANT arrays > (including grid scalars) are assumed to be the same on all > processors". Certainly many grid arrays with DISTRIB=CONSTANT (eg. the > SphericalSurface radius arrays) behave like this. > > PUGH/IOASCII on the other hand seems to not make this assumption. In > PUGH's case according to line 721 of SetupPGV.c > --8<-- > /* A -ve size means constant load per proc */ > if (sh[dir] < 0) > { > if (local_size_includes_ghosts) > { > this->nsize[dir] = (nprocs[dir]-2) * > (-sh[dir] - 2*nghosts[dir]) + > 2 * (-sh[dir] - nghosts[dir]); > } > else > { > this->nsize[dir] = nprocs[dir] * (-sh[dir]); > } > } > --8<-- > Cactus would even allow ghost points for DISTRIB=CONSTANT arrays. This > seems strange to me (and makes trying to make IOASCII behave the way > CarpetIOASCII does much harder). If the array is not distributed > across processes, why would there be ghost zones? Would it not make > more sense to actively forbid GHOSTSIZE>0 for DISTRIB=CONSTANT grid > arrays? In that case the local_size_includes_ghosts stuff is also not > needed since nghosts would always be zero when sh[dir] < 0 (which PUGH > uses to indicate DISTRIB=CONSTANT arrays). > > Yours, > Roland > > -- > My email is as private as my paper mail. I therefore support encrypting > and signing email messages. Get my PGP key from http://keys.gnupg.net. > > _______________________________________________ > Users mailing list > [email protected] > http://cactuscode.org/mailman/listinfo/users -- Erik Schnetter <[email protected]> http://www.perimeterinstitute.ca/personal/eschnetter/ My email is as private as my paper mail. I therefore support encrypting and signing email messages. Get my PGP key from http://pgp.mit.edu/.
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