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4.1 Running on parallel machines
Parallel execution is strongly system- and installation-dependent. 
Typically one has to specify:
- a launcher program (not always needed), 
such as poe, mpirun, mpiexec,
  with the  appropriate options (if any);
- the number of processors, typically as an option to the launcher
  program, but in some cases to be specified after the name of the
  program to be
  executed; 
- the program to be executed, with the proper path if needed: for
  instance, ./neb.x, or $HOME/bin/neb.x, or
  whatever applies; 
- other PWscf-specific parallelization options, to be
  read and interpreted by the running code; 
- the number of image groups used by NEB (see next subsection).
Items 1) and 2) are machine- and installation-dependent, and may be 
different for interactive and batch execution. Note that large
parallel machines are  often configured so as to disallow interactive
execution: if in doubt, ask your system administrator.
Item 3) also depend on your specific configuration (shell, execution
path, etc). 
Item 4) is optional but may be important: see the following section
for the meaning of the various options.
For illustration, here is how to run neb.x  on 16 processors partitioned into
4 image groups (4 processors each), for a path containing at least 4 images with POE:
   poe neb.x -procs 16 -ni 4 -i input
 
 
 
 
 
 
 
  
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