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NAME

       mpif90 -- Open MPI Fortran 90 wrapper compiler

SYNTAX

       mpif90 [-showme|-showme:compile|-showme:link] ...

OPTIONS

       -showme
              Do  not  invoke  the  underlying  compiler.   Instead,  show the
              command line that would be  executed  to  compile  the  program.
              NOTE:  If a non-filename argument is passed on the command line,
              the -showme option will not display any additional  flags.   For
              example,   both   "mpif90   --showme"   and   "mpif90   --showme
              my_source.c" will show  all  the  wrapper-supplied  flags.   But
              "mpif90  -showme -v" will only show the underlying compiler name
              and "-v".

       -showme:compile
              Do not invoke the underlying Fortran 90 compiler.  Instead, show
              the  compiler  flags  that  would  be supplied to the Fortran 90
              compiler.

       -showme:link
              Do not invoke the underlying Fortran 90 compiler.  Instead, show
              the  linker  flags  that  would  be  supplied  to the Fortran 90
              compiler.

       See the man page for your underlying compiler for  other  options  that
       can be passed through mpif90

DESCRIPTION

       Conceptually, the role of these commands is quite simple: transparently
       add relevant compiler and linker flags to the user’s command line  that
       are  necessary to compile / link Open MPI programs, and then invoke the
       underlying compiler to actually perform the command.

       As such,  these  commands  are  frequently  referred  to  as  "wrapper"
       compilers  because  they  do  not actually compile or link applications
       themselves; they only add in command line flags and invoke the back-end
       compiler.

   Background
       Open  MPI  is  comprised  of three software layers: OPAL (Open Portable
       Access Layer), ORTE (Open Run-Time Environment), and OMPI  (Open  MPI).
       There  are  wrapper compilers for each layer; each layer’s wrapper only
       links in the libraries relevant for  that  layer.   Specifically,  each
       layer provides the following wrapper compilers:

       OPAL
           opalcc and opalc++

       ORTE
           ortecc and ortec++

       OMPI
           mpicc,  mpic++,  mpicxx,  mpiCC (only on systems with case-senstive
           file systems), mpif77, and mpif90.  Note that mpic++,  mpicxx,  and
           mpiCC  all  invoke  the  same underlying C++ compiler with the same
           options.   All  are  provided  as  compatibility  with  other   MPI
           implementations.

       The  Fortran  wrapper  compilers  for  MPI  (mpif77 and mpif90) will be
       inoperative and will return an error on use if Fortran 77 / Fortran  90
       support was not built into the MPI layer.

   Overview
       mpif90  is  a  convenience  wrappers  for  the  underlying  Fortran  90
       compiler.  Translation of an Open MPI program requires the  linkage  of
       the  Open  MPI-specific  libraries  which  may not reside in one of the
       standard search directories of  ld(1).   It  also  often  requires  the
       inclusion  of  header  files  what  may also not be found in a standard
       location.

       mpif90 passes its arguments to the underlying Fortran 90 compiler along
       with the -I, -L and -l options required by Open MPI programs.

       The  Open  MPI  Team  strongly  encourages  using the wrapper compilers
       instead of attempting to link to the Open MPI libraries manually.  This
       allows  the  specific  implementation  of  Open  MPI  to change without
       forcing changes to linker directives in users’ Makefiles.  Indeed,  the
       specific  set  of  flags  and  libraries  used by the wrapper compilers
       depends on how Open MPI was configured and built; the values can change
       between different installations of the same version of Open MPI.

       Indeed,  since  the  wrappers  are  simply  thin  shells  on  top of an
       underlying compiler, there are very, very few compelling reasons not to
       use  mpif90.  When it is not possible to use the wrappers directly, the
       -showme:compile and -showme:link options should be  used  to  determine
       what flags the wrappers would have used.  For example:

       shell$ cc -c file1.c ‘mpicc -showme:compile‘

       shell$ cc -c file2.c ‘mpicc -showme:compile‘

       shell$ cc file1.o file2.o ‘mpicc -showme:link‘ -o my_mpi_program

NOTES

       It is possible to make the wrapper compilers multi-lib aware.  That is,
       the libraries and includes specified may differ based on  the  compiler
       flags  specified  (for  example,  with  the  GNU  compilers on Linux, a
       different library path may be used if -m32 is seen  versus  -m64  being
       seen).   This  is not the default behavior in a standard build, but can
       be activated (for example, in a binary package providing both 32 and 64
       bit support).  More information can be found at:

         https://svn.open-mpi.org/trac/ompi/wiki/compilerwrapper3264

FILES

       The  string  that  the  wrapper  compilers insert into the command line
       before invoking the underlying compiler  are  stored  in  a  text  file
       created  by Open MPI and installed to $pkgdata/mpif90-wrapper-data.txt,
       where $pkgdata is typically $prefix/share/openmpi, and $prefix  is  the
       top installation directory of Open MPI.

       It  is  rarely  necessary  to edit this file, but it can be examined to
       gain insight into what flags the wrappers are placing  on  the  command
       line.

ENVIRONMENT VARIABLES

       By default, the wrappers use the compilers that were selected when Open
       MPI was configured.  These compilers were either found automatically by
       Open  MPI’s "configure" script, or were selected by the user in the CC,
       CXX, F77,  and/or  FC  environment  variables  before  "configure"  was
       invoked.   Additionally,  other  arguments specific to the compiler may
       have been selected by configure.

       These values can be selectively overridden by either editing  the  text
       files   containing   this  configuration  information  (see  the  FILES
       section), or by setting selected  environment  variables  of  the  form
       "OMPI_value".

       Valid value names are:

       CPPFLAGS
              Flags added when invoking the preprocessor (C or C++)

       LDFLAGS
              Flags added when invoking the linker (C, C++, or Fortran)

       LIBS   Libraries added when invoking the linker (C, C++, or Fortran)

       CC     C compiler

       CFLAGS C compiler flags

       CXX    C++ compiler

       CXXFLAGS
              C++ compiler flags

       F77    Fortran 77 compiler

       FFLAGS Fortran 77 compiler flags

       FC     Fortran 90 compiler

       FCFLAGS
              Fortran 90 compiler flags