Re: Ada vs Fortran for scientific applications

[Brooks Moses <bmoses-nospam@cits1.stanford.edu>]

Nasser Abbasi wrote:
> I like to discuss the technical reasons why Ada is not used as much as 
> Fortran for scientific and number crunching type applications?
> 
> To make the discussion more focused, let's assume you want to start 
> developing a large scientific application in the domain where Fortran is 
> commonly used. Say you want to develop a new large Finite Elements Methods 
> program or large computational physics simulation system. Assume you can 
> choose either Ada or Fortran.
> 
> What are the technical language specific reasons why Fortran would be 
> selected over Ada?

In my case?  I know Fortran.  I don't know Ada.  I would be foolish to 
attempt to learn a new language while writing a large program that I 
needed to rely on.

> I happened to know a little about Ada and Fortran, and from what I know, I 
> think Ada would be an excellent choice due to its strong typing, good 
> support for numerical types and good Math library.

Quite probably.  Many languages are.

I'm rapidly becoming of the opinion that, once languages hit a minimum 
level of functionality sufficient to be capable of solving the problem 
at hand -- and, for scientific processing, that generally means "does it 
avoid doing something stupid with basic array math?" and "can it link to 
an appropriate parallel-processing library" -- the relevant questions 
are all about the available programmers and the character of the 
interface between the programmer and the language.  Some languages are 
vastly easier to program in than others -- but which one is which 
depends on the programmers you have and what they're trying to do.

> I know also that Fortran is supposed to be better/faster when it comes to 
> working with large Arrays (Matrices), but it is not clear to me why that is, 
> and if it is still true with Ada 05. Something about arrays aliasing, but 
> not sure how that is.

This may be true to a minor extent; I doubt that there is any major 
fundamental difference.  In general, "Which language is faster?" is a 
meaningless question.

To take a well-populated example, consider that for Fortran on Intel 
desktop computers there are usually significant variations (10 to 20 
percent seems very common) in the speed of the exact same program when 
compiled on different compilers -- and that's just the mature compilers. 
  With less-mature compilers, such as early versions of g95 and 
gfortran, there can be differences of a factor of two or three in speed.

Now, it is highly unlikely that the Ada language has anything in it that 
will cause more than a few percentage points of difference in the 
maximum theoretically-achievable speed.  Thus, in practice any speed 
differences are going to be almost entirely a factor of the quality of 
the code you write, and the quality of the compiler you compile it on.

The only way the language is likely to be relevant is if you are writing 
the code for a platform where there aren't any high-quality compilers 
for the language you're using.  My completely unfounded guess is that 
this is more likely to be true for Ada than it is for Fortran, simply 
because of popularity, but it could be completely the reverse for the 
system you're using.

Thus, it's far more important to look at the compilers you have 
available, and do your own tests on comparable code similar to your 
expected application, than it is to worry about minor theoretical 
details about "which language is faster".

> I am also not sure on the support of sparse matrices in both languages' 
> libraries.

I'd be fairly surprised if there weren't decent sparse matrix libraries 
available for both languages.  Probably lots of them, with a vast range 
of quality.

> It is known that Ada strong domain is realtime and safety critical 
> applications. I never understood why Ada never became popular in the 
> scientific field in particular in areas such as computational physics or CFD 
> or such similar fields.

I have no idea; by the time I reached college, that popularity contest 
had already been settled, and my intro-to-engineering class taught 
Fortran and didn't teach Ada.

- Brooks, posting from comp.lang.fortran


-- 
The "bmoses-nospam" address is valid; no unmunging needed.