/** @page iosystem Initializing the IO System

Using PIO begins with initializing the IO System. This sets up the MPI
communicators with the computational and I/O processors.

When the IO System is created, an IOSystem ID is returned and must be
used in future PIO calls. The IOSystem ID is returned by C functions
PIOc_Init_Intracomm() and PIOc_init_async(). Fortran users see @ref
PIO_init.

When the user program is complete, the IOSystem should be released by
calling C function PIOc_finalize() or Fortran function piolib_mod::finalize()
for each open IOSystem.

@section intracomm_mode Intracomm Mode

@image html PIO_Intracomm1.png "PIO Intracomm Mode"

@section async_mode Async Mode

@image html PIO_Async.png "PIO Async Mode"

*/
