Numerical Recipes in Fortran 90 - The Art of Scientific Parallel Computing

Peter Kitson

ISBN : 0521437210

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Sample Chapter From Numerical Recipes in Fortran 90 - The Art of Scientific Parallel Computing
     Copyright © William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling



Chapter 21. Introduction to Fortran 90 Language Features

21.0 Introduction

Fortran 90 is in many respects a backwards-compatible modernization of the
long-used (and much abused) Fortran 77 language, but it is also, in other respects,
a new language for parallel programming on present and future multiprocessor
machines. These twin design goals of the language sometimes add confusion to the
process of becoming fluent in Fortran 90 programming.

In a certain trivial sense, Fortran 90 is strictly backwards-compatible with
Fortran 77. That is, any Fortran 90 compiler is supposed to be able to compile
any legacy Fortran 77 code without error. The reason for terming this compatibility
trivial, however, is that you have to tell the compiler (usually via a source file name
ending in “.f” or “.for”) that it is dealing with a Fortran 77 file. If you instead
try to pass off Fortran 77 code as native Fortran 90 (e.g., by naming the source file
something ending in “.f90”) it will not always work correctly!

It is best, therefore, to approach Fortran 90 as a new computer language, albeit
one with a lot in common with Fortran 77. Indeed, in such terms, Fortran 90 is a
fairly big language, with a large number of new constructions and intrinsic functions.
Here, in one short chapter, we do not pretend to provide a complete description
of the language. Luckily, there are good books that do exactly that. Our favorite
one is by Metcalf and Reid [1], cited throughout this chapter as “M&R.” Other good
starting points include [2] and [3].

Our goal, in the remainder of this chapter, is to give a good, working description
of those Fortran 90 language features that are not immediately self-explanatory
to Fortran 77 programmers, with particular emphasis on those that occur most
frequently in the Fortran 90 versions of the Numerical Recipes routines. This
chapter, by itself, will not teach you to write Fortran 90 code. But it ought to help
you acquire a reading knowledge of the language, and perhaps provide enough of
a head start that you can rapidly pick up the rest of what you need to know from
M&R or another Fortran 90 reference book.

CITED REFERENCES AND FURTHER READING:
Metcalf, M., and Reid, J. 1996, Fortran 90/95 Explained (Oxford: Oxford University Press). [1]
Kerrigan, J.F. 1993, Migrating to Fortran 90 (Sebastopol, CA: O’Reilly). [2]
Brainerd, W.S., Goldberg, C.H., and Adams, J.C. 1996, Programmer’s Guide to Fortran 90, 3rd
ed. (New York: Springer-Verlag). [3]