Re: problems converting Fortran 77 code to Fortran 90

From: Benjamin Johnson (jbenjam_at_aos.wisc.edu)
Date: 01/20/05 

Date: Thu, 20 Jan 2005 14:30:15 -0600

On Thu, 20 Jan 2005, Richard E Maine wrote:

> Well, I didn't really bother to study this in detail (other work calls),
> but you seem to be mixing up a lot of unrelated things, few of which
> have anything to do with the stated objective.

True, stated objective is (mostly) independent of the question I was
asking. I did not make any *intentional* computational changes to the
code.

The issue I was facing was: after "converting" to a form in which intel
fortran compiler would compile it with a .f90 extension, I was getting
different results. However, upon following your suggestion of one change
at a time, I find that indeed I must have inadvertently changed
"something", because the results are consistent now. I made too many
assumptions -- a character flaw at best.

> One of the really fundamental principles of tracking down differences
> caused by changes: only make one change at a time.

> I won't address the question of whether any of this is likely to achieve
> your stated goal of reducing computational time... except that I'll note
> that it is not a given. Using f90 intrinsics isn't a magic bullet that
> will automatically help computation time. Might help. Might hurt.

It should in this case: 8 million calls to the subroutine MMULT I gave in
the original post vs. 8 million calls to the MATMUL intrinsic.

> Again, all these comments are pretty cursory and not based on serious
> study of the code. I just noticed you mentioning a lot of changes that
> had nothing to do with your stated goals... and then your asking what
> caused the differences.

You must have experienced these kinds of "ambiguous" posts quite often.
   I will try to be more "diligent" in my descriptions and approach in the
future.

On a completely unrelated note: I see that you work for NASA Dryden -- I'm
at Goddard now, and am enjoying working here thus far, However, they are
very strict about certain things, such as posting to newsgroups using NASA
computers (according to the regulations). Does Dryden have similar rules?
I'm hesistant to post through google or something similar using my office
box, so I use my university account to do it...

Also, I saw that a "Richard Maine" at Dryden was once an astronaut
candidate, is that you?

-Ben

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