Notes on compiler optimization levels for Sun and IBM

Dear users,

If you are running the Sun MPI version (section 7i of the configure.user file), you should be aware of a problem with the "-fast" compiler option that can result in an immediate core dump at execution time. We experienced this with both the tmf77 and tmf90 compilers, Sun WorkShop 6 update 2:

tmf90 -V
Sun WorkShop 6 update 2 Fortran 95 6.2 2001/05/15

When we used "-O4" instead of "-fast" (in both FCFLAGS and LDOPTIONS), the executable ran successfully. Also, please check the file MPP/RSL/RSL/makefile.sunmpi and make sure COPTIM and FOPTIM are set as follows:

  COPTIM =  -O
  FOPTIM =  -O

After any changes to the makefile.sunmpi file, type "make uninstall" and "make mpp" from the main directory level.

If you are running on an IBM-SP machine (section 7a or 7a.1 of the configure.user file), you should be aware that the "-O3" level compiler optimization can result in NaNQ values in your model output. This has only been observed when running with nests. In this case, you should use "-O2" instead.

Thanks

Thanks to user Ivan Gelpi of the University of Santiago de Compostela in Spain for his persistence and help in tracking down the optimization problem on the Sun system.

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Rotang, Aug 2, 2001