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dgscat(1)		    PT-Scotch user's manual		     dgscat(1)

NAME
       dggath,	dgscat,	 gscat	- convert distributed source graphs to or from
       centralized ones

SYNOPSIS
       dggath [options] [igfile] [ogfile]

       dgscat [options] [igfile] [ogfile]

       gscat [options] [igfile] [ogfile]

DESCRIPTION
       The dggath program gathers distributed graphs into centralized  graphs.
       It  reads a set of files igfile representing fragments of a distributed
       source graph, and writes them back on the form of a single  centralized
       source graph ogfile.

       The  dgscat program scatters centralized source graphs into distributed
       graphs. It reads a centralized source graph igfile and writes  it  back
       on the form of a set of files ogfile representing fragments of the cor‐
       responding distributed source graph.

       The gscat program does exactly the same as dgscat, but does not require
       to  be  run  in a parallel environment. Since gscat processes the input
       centralized graph file as a text stream, it does not need to  load  the
       full  graph  in	memory	before building the distributed graph fragment
       files. It is therefore much less resource consuming, but does not allow
       for  the	 checking  of graph consistency, as it has no global vision of
       the graph structure.

       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,	dggath
       and  dgscat  can	 directly  handle compressed graphs, both as input and
       output. A stream is treated as compressed whenever its  name  is	 post‐
       fixed  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).

       dggath and dgscat base 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 sin‐
       gle 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	direc‐
	      tories  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, respec‐
	      tively (but in this latter case it is much recommended to	 iden‐
	      tify 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.

For  instance,	filename 'brol' will lead to the opening of file 'brol' on the
root processor only, filename '%-brol' (or even 'br%-ol')  will	 lead  to  the
parallel  opening  of  files  called  'brol'  on every processor, and filename
'brol%p-%r' will lead to the opening of files on which	the  program  were  to
run.

OPTIONS
       -c     For  dggath  and dgscat only. 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 dgscat on 5 processing elements to scatter centralized  graph  file
       brol.grf	   into	  5   gzipped	file   fragments   brol5-0.dgr.gz   to
       brol5-4.dgr.gz.

	   $ mpirun -np 5 dgscat brol.grf brol%p-%r.dgr.gz

SEE ALSO
       dgmap(1), dgord(1), dgtst(1), gmk_hy(1).

       PT-Scotch user's manual.

AUTHOR
       Francois Pellegrini <francois.pellegrini@labri.fr>

			       February 14, 2011		     dgscat(1)
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