Because HPF is designed as a high-level, machine-independent language,
there are certain operations that are difficult or impossible to
express directly. For example, many applications benefit from
finely-tuned systolic communications on certain machines; HPF's global
address space does not express this well. Extrinsic procedures define
an explicit interface to procedures written in other paradigms, such as
explicit message-passing subroutine libraries. Section
describes this interface. Annex gives a specific
interface for HPF_LOCAL routines, for
HPF_SERIAL routines, and for Fortran 90.