[Rd] additional comments on building R with PGI compiler

[Jennifer Lai]

Hi,
   I have additional comments on building R with PGI compiler.
If one wants to use external BLAS library, then pgf90 instead of pgf77 
should be used, and BLAS_LIBS flags should be set.

e.g.
F77 = $PG_HOME/bin/pgf90
BLAS_LIBS='-L/opt/acml2.7.0/pgi64/ -lacml'      # for ACML library
BLAS_LIBS='-L/usr/lib64 -lg2c -lblas'                 # for generic BLAS 
library that comes with OS distribution.

Regards,
Jennifer