Is this MPICH, or IBM MPI?

That dichotomy is dated, but not particularly relevant for this discussion.

When I install MPICH 3.x on my Linux commodity cluster, I only see mpif77 and mpif90. Does MPICH do something different when installed on a BG system?

IBM deploys MPICH for BG with a bunch of wrappers, one for each bgxl* compiler (including an _r variant for each as well). They are named mpixl* to prevent confusion with the GCC wrappers, at least when some variants of MPI are used. See https://wiki.alcf.anl.gov/parts/index.php/Mira_MPI_Documentation#Explanation... for details. If you have further questions, request an ALCF account and you can dig around yourself :-)

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By default, XLF does not enforce strict language compliance, but it will enforce a wide range of syntax requirements that cause user codes to fail to compile. I recall more than one case where Fortran 2003 and 2008 differ just slightly and users have to use the compiler associated with precisely the language that they are trying to use.

Fair enough.

But I'm trying to determine if MPICH really has mpif03 and mpif08, or whether you were using IBM's MPI, or whether you used MPICH's "mpif90" with some appropriate flag to force a particular syntax/dialect.

MPICH does not have these, but I don't see why it would today given that it only supports the F77 and F90 interfaces. Whether or not mpif08 is required depends on whether or not the Fortran compiler is indifferent to all syntax between 1990 and 2008+. Jeff -- Jeff Hammond [email protected]