/*D mpiexec - Run an MPI program

   Synopsis:
.vb
    mpiexec args executable pgmargs [ : args executable pgmargs ... ]
.ve
   where 'args' are command line arguments for 'mpiexec' (see below), 
   'executable' is the name of an executable MPI program, and 'pgmargs'
   are command line arguments for the executable.  Multiple executables 
   can be specified by using the colon notation (for MPMD - Multiple Program
   Multiple Data applications).   For example, the following command will run
   the MPI program 'a.out' on 4 processes\:
.vb
    mpiexec -n 4 a.out
.ve

The MPI standard specifies the following arguments and their meanings\:

+ \-n <np> - Specify the number of processes to use
. \-host <hostname> - Name of host on which to run processes
. \-arch <architecture name> - Pick hosts with this architecture type
. \-wdir <working directory> - cd to this one `before` running executable
. \-path <pathlist> - use this to find the executable
. \-soft <triplets> - comma separated triplets that specify requested numbers
   of processes (see the MPI-2 specification for more details)
. \-file <name> - implementation-defined specification file
- \-configfile <name> - file containing specifications of host/program,
   one per line, with # as a comment indicator, e.g., the usual
   mpiexec input, but with ":" replaced with a newline.  That is,
   the configfile contains lines with -soft, -n etc.

   Additional arguments that are specific to the MPICH implementation
   are discussed below.

   Note that not all of these parameters are meaningful for all 
   systems.  For example, the 'gforker' version of 'mpiexec' creates all
   processes on the same system on which it is running; in that case, the 
   '\-arch' and '\-host' options are ignored.

   The colon character (':') may be used to separate different executables
   for MPMD (multiple program multiple data) programming.  For example,
   to run the program 'ocean' on 4 processes and 'air' on 8 processes, use\:

.vb
    mpiexec -n 4 ocean : -n 8 air
.ve

         
   MPICH-Specific Arguments:
   
   MPICH implements a few process managers. Here we list a general set of
   arguments that many of the implementations support. More detailed options
   that are supported by a particular implementation, e.g. hydra, are
   available via\:
.vb
    mpiexec -h
.ve

   Many of the implementations of process managers in MPICH support the
   following arguments to 'mpiexec'\:

+ \-np <num> - A synonym for the standard '\-n' argument
. \-env <name> <value> - Set the environment variable '<name>' to '<value>' for
   the processes being run by 'mpiexec'
.  \-envnone - Pass no environment variables (other than ones specified with
   other '\-env' or '\-genv' arguments) to the processes being run by 'mpiexec'.
   By default, all environment
   variables are provided to each MPI process (rationale: principle of
   least surprise for the user)
.  \-envlist <list> - Pass the listed environment variables (names separated
 by commas), with their current values, to the processes being run by
 'mpiexec'.
. \-genv <name> <value> - The '\-genv' options have the same meaning as their
 corresponding '\-env' version, except they apply to all executables, not just
 the current executable (in the case that the colon syntax is used to specify
 multiple executables).
.  \-genvnone - Like '\-envnone', but for all executables
.  \-genvlist <list> - Like '\-envlist', but for all executables
.  \-usize <n> - Specify the value returned for the value of the attribute
  'MPI_UNIVERSE_SIZE'.
.  \-l - Label standard out and standard error ('stdout' and 'stderr') with
  the rank of the process
.  \-maxtime <n> - Set a timelimit of '<n>' seconds.
-  \-exitinfo - Provide more information on the reason each process exited if
   there is an abnormal exit

   Environment variables for mpiexec:
  The following environment variables are understood by some versions of 
  'mpiexec'.  The command line arguments have priority over these; that is,
  if both the environment variable and command line argument are used, the
  value specified by the command line argument is used.  

+ MPIEXEC_TIMEOUT  - Maximum running time in seconds.  'mpiexec' will
  terminate MPI programs that take longer than the value specified by
  'MPIEXEC_TIMEOUT'.  
. MPIEXEC_UNIVERSE_SIZE - Set the universe size
. MPIEXEC_PORT_RANGE - Set the range of ports that 'mpiexec' will use 
  in communicating with the processes that it starts.  The format of 
  this is '<low>:<high>'.  For example, to specify any port between
  10000 and 10100, use '10000:10100'.  
. MPICH_PORT_RANGE - Has the same meaning as 'MPIEXEC_PORT_RANGE' and 
  is used if 'MPIEXEC_PORT_RANGE' is not set.

   Return Status:
   'mpiexec' returns the maximum of the exit status values of all of the
   processes created by 'mpiexec'.  
   
D*/
