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An extrinsic function is a function written in a language other than HPF including most naturally any node programming language (e.g. Fortran77) targeted to a single processor SPMD) with message passing such as MPI
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HPF defines (Fortran90) interface and invocation characteristics
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This defines what is input and output via INTENT and these rules must be obeyed by callee (non HPF side)
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If variables are implicitly replicated, the callee must make them consistent before reurn i.e. callee must respect HPF model of parallelism
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HPF will execute any remapping commands and hands callee the "right" part of any distributed arrays
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All processors are synchronized before call to EXTRINSIC function
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Allows one to get efficient parallel code where HPF language or compiler inadequate
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Analogous to calling assembly language from Fortran, Native classes from Java, C from PERL etc.
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