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From: robin on 13 Aug 2010 10:46
"Ron Shepard" <ron-shepard(a)NOSPAM.comcast.net> wrote in message
news:ron-shepard-9FD13E.16323410082010(a)news60.forteinc.com...
| In article <Rd2dndSu6ZUm4PzRnZ2dnUVZ7v4AAAAA(a)giganews.com>,
| Vincenzo Mercuri <comp(a)lang.c> wrote:
|
| > I've been always told of the C language as the best choice
| > to accomplish any kind of task in numerical algorithms implementation.
|
| Maybe newer versions of C are better, but the older versions of C were
| particularly bad when it came to numerical algorithms. For example, in
| traditional K&R C, parentheses could not be used to force operations to
| occur in a particular order, something that is very important when
| writing numerical code. Also, float arguments were promoted to double
| in all function calls, another troublesome feature when trying to write
| careful numerical code. And, of course, all arrays in C must be
| zero-based, which seldom matches the numerical problem at hand.
| Multidimensional arrays are also a problem in C, especially the ones
| with dimensions determined at runtime rather than with constants at
| compile time. The floating point declarations sometimes are a pain in
| C. For example, something declared as float on one machine might have
| the same precision as something declared as double or as long double on
| some other machine. And finally, perhaps the biggest problem with
| numerical code in C, is that the value of some simple expressions such
| as "i/j" in which either one or both of the integer values are negative
| were not defined in C (they could round either up or down); this means
| that to write truly portable C code you need to test for negative values
| and evaluate the expressions using positive values only.
|
| All these things are much better in fortran. Fortran has always
| respected parentheses in expressions, and fortran has never silently
| promoted arguments in subroutine calls. Fortran does allow mixed-mode
| and mixed-precision expressions, which are sort of like promotion, but
| the programmer has control over this in fortran by the way the
| expressions are written. Arrays in fortran can have any base at all,
| whatever best fits the problem at hand. Multidimensional arrays in
| fortran are no problem, they are as easy to declare, use, allocate, or
| deallocate as 1D arrays. Newer versions of fortran (since 1990) have a
| nice way of parameterizing floating point precision that avoids many of
| the portability problems in ancient fortrans (f77 and earlier); C has
| not yet caught up in this respect. And, "i/j" has always had a
| well-defined value in fortran for any combination of negative or
| positive integers (well, j cannot be zero, but that is a different
| issue). Also, fortran has a nice array syntax which allows complicated
| expressions to be expressed in a simple way, very much like the
| mathematical expression you would write on paper; being able to write
| clear, simple, code is important in numerical work.

The same things can be said about PL/I.
It was designed for implementing numerical algorithms,
(among other things). In particular, it was designed
to perform array-valued operations some 25 years before
Fortran had them. As well, it provides for error recovery,
one of the banes of numerical programs in other languages.

| I would say that it is difficult to even think of a numerical problem
| that can be done better in C than in fortran.

Agreed.


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