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
       corresponding 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
       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).

       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  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.

       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  'brol2-0'  and  'brol2-1',
       respectively, on each of the two processors 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>

                                                 August 03, 2010                                       dgscat(1)