Fortran 90: a conversion course for Fortran 77 programmers

105 Pages·1990·0.22 MB·English

by  Walter S. Brainerd, Charles H. Goldberg, Jeanne C. Adams

Fortran 90
A Conversion Course
for Fortran 77 Programmers
Student Notes
S Ramsden, F Lin
Manchester and North HPC T&EC
M A Pettipher, G S Noland, J M Brooke
Manchester Computing Centre, University of Manchester
Edition 3.0 July 1995

Acknowledgements
These student notes were developed using the Manchester Computing Centre Fortran
90 course, which was compiled by J M Brooke, G S Noland, and M A Pettipher as a
basis.
Useful comments were also provided by the following: T L Freeman, J Gajjar and A J
Grant (The University of Manchester), and A Marshall and J S Morgan (The Univer-
sity of Liverpool).
Michael Hennecke, University of Kahlsruhe, Germany, provided comprehensive com-
ments which were incorporated in edition 3.0 of the materials.
Manchester and North HPC T&EC i
Fortran 90
ii Fortran 90 Student Notes
Table of Contents
1 Introduction
1 History
1 Objectives
1 Language Evolution
2 New Features
3 Organisation
3 Coding Convention
5 Sources, Types and Control Structures
5 Source Form
6 Program and Subprogram Names
6 Specifications
7 Strong Typing
7 The Concept of KIND
10 Derived Types
13 Control Statements
17 Exercises
19 Procedures and Modules
19 Program Units
20 Procedures
28 Modules
31 Overloading
35 Scope
36 Program Structure
39 Exercises
41 Array Processing
41 Terminology and Specifications
43 Whole Array Operations
45 Elemental Intrinsic Procedures
45 WHERE Statement
46 Array Sections
48 Array Assignment
48 Recursion
48 Element Location Versus Subscript
49 Zero Sized Arrays
Manchester and North HPC T&EC iii
Fortran 77 to Fortran 90
49 Array Constructors
50 Allocatable Arrays
52 Automatic Arrays
54 Assumed Shape Arrays
56 Array Intrinsics
58 Array Example
60 Exercises
63 Pointer Variables
63 What is a Pointer
63 Specifications
64 Pointer Assignments
66 Pointer Association Status
67 Dynamic Storage
68 Pointer Arguments
69 Pointer Functions
69 Arrays of Pointers
70 Linked List
73 Exercises
75 Input/Output
75 Non-advancing I/O
76 INQUIRE by I/O List
76 NAMELIST
77 New Edit Descriptors
77 New Statement Specifiers
79 Exercises
81 Intrinsic Procedures
81 Elemental Procedures
83 Inquiry Functions
84 Transformational Functions
84 Non Elemental Intrinsic Subroutines:
84 Array Intrinsic Procedures
86 Exercises
87 Redundant Features
87 Source Form
87 Data
88 Control
88 Procedures
iv Student notes
88 Input/Output
91 Further Development
91 Fortran 95
92 Parallel Computers
95 References
Manchester and North HPC T&EC v
Fortran 77 to Fortran 90
vi Student notes
Introduction
1 Introduction
This course covers the transition from the programming language Fortran 77 to the
more modern Fortran 90, and is aimed at Fortran 77 programmers who require an
understanding of the principles and new features of Fortran 90. The course may also
be suitable for programmers familiar with languages such as C or Pascal, but not for
complete beginners in programming.
1.1 History
The programming language Fortran was originally designed for the solution of prob-
lems involving numerical computation. The development of Fortran dates back to the
1950s, the first Fortran system being released in 1957, for the IBM 704.
In the early 1960s, as other manufacturers released Fortran compilers for their own
computer systems, the need to control and standardise Fortran became apparent. A
standards committee was established in 1962, and the first Fortran standard was pub-
lished in 1966.
Unfortunately, the 1966 Standard did not give a clear, precise definition of Fortran. In
the 1970s a new standard was formulated to overcome the problems of Fortran 66 and
incorporate several new features. In 1978, the new standard, Fortran 77, was pub-
lished.
The standards preceding Fortran 90 attempted mainly to standardise existing exten-
sions and practices. Fortran 90, however, is much more an attempt to develop the lan-
guage, introducing new features using experience from other languages.
The next Fortran revision is expected within the next 10 years.
1.2 Objectives
The objectives of the new Fortran 90 standard were:
• to modernise the language in response to the developments in language design
which have been exploited in other languages.
• to standardise vendor extensions such that an efficient portable language is pro-
vided.
• to improve the safety of programming in the language and to tighten the con-
formance requirement, such that the risk of error in standard code is reduced.
• to keep compatible with Fortran 77 by adopting a language evolution method
such that the vast investment in Fortran 77 code is preserved.
1.3 Language Evolution
Fortran 90 is a superset of Fortran 77, and so all standard Fortran 77 programs should
run. To prevent the language growing progressively larger, however, as new revisions
Manchester and North HPC T&EC 1
Fortran 90
are produced, the standards committee has adopted a policy of removing obsolete
features.
This procedure adopted involves the inclusion of two lists with each new standard.
One list contains the deleted features, and the other contains the obsolescent features.
The obsolescent list consists of features which are considered to be redundant and
may be deleted in the next revision. A feature must appear on the obsolescent list
before it can be deleted, thus providing a period of notice of at least one revision cycle.
Fortran 90 contains no deleted features, but contains the following obsolescent fea-
tures which may be removed at the next revision.
• ArithmeticIF
• REAL andDOUBLEPRECISIONDO variables and control expressions
• SharedDO termination, andDO termination on a statement other than on aCON-
TINUE or anEND DO statement
• ASSIGN and assigned GOTO statements
• AssignedFORMAT specifiers
• Branching toEND IF from outsideIF block
• AlternateRETURN
• PAUSE statement
• H edit descriptor
1.4 New Features
The following major new features are included in Fortran 90:
• Array processing
• Dynamic memory allocation, including dynamic arrays
• Modules
• Procedures:
• Optional/Keyword Parameters
• Internal Procedures
• Recursive Procedures
• Pointers
Other new features include:
• Free format source code
• Specifications/IMPLICIT NONE
• Parameterised data types
• Derived types
• Operator overloading
• CASE statement
• EXIT andCYCLE
• Many new intrinsic functions
• New I/O features
2 Fortran 90 Student Notes