NAME
ptscotch_dgscat - build distributed source graph file fragments from a
centralized source graph file
SYNOPSIS
ptscotch_dgscat [options] [igfile] [ogfile]
DESCRIPTION
The ptscotch_dgscat program reads a centralized source graph igfile and
writes it back on the form of a set of files ogfile representing
fragments of a distributed source graph.
When file names are not specified, data is read from standard input and
written to standard output. Standard streams can also be explicitly
represented by a dash ’-’.
When the proper libraries have been included at compile time, dgord can
directly handle compressed graphs, both as input and output. A stream
is treated as compressed whenever its name is postfixed with a
compressed file extension, such as in ’brol.grf.bz2’ or ’-.gz’. The
compression formats which can be supported are the bzip2 format
(’.bz2’), the gzip format (’.gz’), and the lzma format (’.lzma’, on
input only).
dgord bases on implementations of the MPI interface to spread work
across the processing elements. It is therefore not likely to be run
directly, but instead through some launcher command such as mpirun.
DISTRIBUTED FILE NAMES
In order to tell whether programs should read from, or write to, a
single file located on only one processor, or to multiple instances of
the same file on all of the processors, or else to distinct files on
each of the processors, a special grammar has been designed, which is
based on the ’%’ escape character. Four such escape sequences are
defined, which are interpreted independently on every processor, prior
to file opening. By default, when a filename is provided, it is assumed
that the file is to be opened on only one of the processors, called the
root processor, which is usually process $0$ of the communicator within
which the program is run. The index of the root processor can be
changed by means of the -r option. Using any of the first three escape
sequences below will instruct programs to open in parallel a file of
name equal to the interpreted filename, on every processor on which
they are run.
%p Replaced by the number of processes in the global communicator
in which the program is run. Leads to parallel opening.
%r Replaced on each process running the program by the rank of this
process in the global communicator. Leads to parallel opening.
%- Discarded, but leads to parallel opening. This sequence is
mainly used to instruct programs to open on every processor a
file of identical name. The opened files can be, according
whether the given path leads to a shared directory or to
directories that are local to each processor, either to the
opening of multiple instances of the same file, or to the
opening of distinct files which may each have a different
content, respectively (but in this latter case it is much
recommended to identify files by means of the ’%r’ sequence).
%% Replaced by a single ’%’ character. File names using this escape
sequence are not considered for parallel opening, unless one or
several of the three other escape sequences are also present.
root processor only, filename ’%-brol’ (or even ’br%-ol’) will lead to the
run.
OPTIONS
-c Check the consistency of the input source graph after loading it
into memory.
-h Display some help.
-rpnum Set root process for centralized files (default is 0).
-V Display program version and copyright.
EXAMPLE
Run ptscotch_dgscat on 5 processing elements to scatter centralized
graph file brol.grf into 5 gzipped file fragments brol5-0.grf.gz to
brol5-4.grf.gz.
$ mpirun -np 5 ptscotch_dgscat brol.grf brol%p-%r.grf.gz
SEE ALSO
ptscotch_dgtst(1), ptscotch_dgord(1), scotch_gmk_hy(1).
PT-Scotch user’s manual.
AUTHOR
Francois Pellegrini <francois.pellegrini@labri.fr>
June 05, 2008 ptscotch_dgscat(1)