Introduction to Programming with Fortran

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1 Introduction to Programming with Fortran

2 Ian D. Chivers and Jane Sleightholme Introduction to Programming with Fortran With Coverage of Fortran 90, 95, 2003, and 77

3 Ian D. Chivers, BSc, PGCEd, MSc, MBCS Rhymney Consulting UK Jane Sleightholme, MSc, MBCS Kings College London UK British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Control Number: ISBN-10: eisbn Printed on acid-free paper ISBN-13: Springer-Verlag London Limited 2006 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Printed in the United States of America (MVY) Springer Science+Business Media springeronline.com

4 Acknowlegement The material in the book has evolved firstly from our combined experience of working in Computing Services within the University of London at King's College, IDC ( ) and JS (1985 to date) Chelsea College, JS ( ) Imperial College, IDC ( ) in the teaching, advice and support of Fortran and related areas, and secondly in the provision of commercial training courses. The following are some of the organisations we've provided training for: AWE, Aldermaston. Centre for Ecology and Hydrology, Wallingford. Environment Agency, Worthing. The Met Office, Bracknell and Exeter. QinetiQ, Farnborough. Rolls Royce, Derby. Veritas DGC Ltd., Crawley. Westland Helicopters, Yeovil. The examples in the book are based on what will work with compilers that support the Fortran 90 and 95 standards and also support ISO TR and At the time of writing this book there are no compilers that fully support the Fortran 2003 standard. Thanks are due to: The staff and students at King's College, Chelsea College and Imperial College.

5 vi Acknowledgement The people who have attended the commercial courses. Its been great fun teaching you and things have been very lively at times. The people on the Fortran 90 list and comp.lang.fortran. Access to the expertise of several hundred people involved in the use and development of Fortran on a daily basis across a wide range of disciplines is inestimable. The people at NAG for the provision of the Fortran 95 compilers and Nag Tools on the enclosed cd. The staff and facilities at PTR Associates. It is a pleasure training there. The patience of our families during the time required to develop the courses upon which this book is based and whilst preparing the camera-ready copy. Finally Rebecca Mowat, Joanne Cooling, Helen Desmond and Beverley Ford at Springer for their enthusiasm and encouragement! Our King's home page is: All of the program examples can be found there. If you would like to contact us our addresses are: Ian D Chivers: ian.chivers@chiversandbryan.co.uk Jane Sleightholme: jane.sleightholme@kcl.ac.uk

6 Contents 1 Overview Introduction to Computer Systems The core of a computer system Central processor unit CPU Memory Bus Other components of a computer system Disks Others Software Problems Bibliography Introduction to Operating Systems History of operating systems The 1940s The 1950s The 1960s The 1960s and 1970s The 1970s, 1980s, and 1990s Networking Problems Bibliography Introduction to Using a Computer System Files Editors Single-user systems Networked systems Multiuser systems Other useful things to know

7 viii Contents 4.7 Common methods of using computer systems to develop Fortran programs Bibliography Introduction to Problem Solving Natural language Artificial language Notations Resumé Algorithms Top-down Bottom-up Stepwise refinement Modular programming Object oriented programming Systems analysis and design Problem definition Feasibility study and fact finding Analysis Design Detailed design Implementation Evaluation and testing Maintenance Conclusions Problems Bibliography Introduction to Programming Languages Some early theoretical work What is a programming language? Program language development and engineering The early days Fortran The Early Days Fortran Cobol Algol Chomsky and program language development Lisp Snobol Second-generation languages PL/1 and Algol Simula Pascal

8 Contents ix APL Basic C Some other strands in language development Abstraction, stepwise refinement and modules Structured programming Standardisation Ada Modula Modula Other language developments Logo Postscript, TeX and LaTeX Prolog SQL ICON Object orientated programming OOP Oberon and Oberon Smalltalk C Java Visual Basic C# Fortran Fortran ISO technical reports TR15580 and TR Fortran DTR enhanced module facilities Internet resources Standards information Fortran discussion lists Other sources Summary Bibliography Introduction to Programming Language strengths and weaknesses Elements of a programming language Data description statements Control structures Data-processing statements Input and output (I/O) statements Variables name, type and value

9 x Contents 7.4 Notes Some more Fortran rules Fortran character set Good programming guidelines Compilers Program development Problems Arithmetic Rounding and truncation Time taken for light to travel from the Sun to Earth The PARAMETER statement Range, precision and size of numbers Health warning: optional reading, beginners are advised to leave until later Selecting different INTEGER kind types Selecting different REAL kind types Specifying kind types for literal integer and real constants Positional number systems Bit data type and representation model Integer data type and representation model Real data type and representation model IEEE Testing the numerical representation of different kind types on a system Binary representation of different integer kind type numbers Binary representation of a real number Summary of how to select the appropriate kind type Variable status Summary Problems Bibliography Arrays 1: Some Fundamentals Tables of data Telephone directory Book catalogue Examination marks or results Monthly rainfall Arrays in Fortran The DIMENSION attribute An index Control structure Monthly rainfall

10 Contents xi Example 1: Rainfall People's weights Example 2: Setting array size with a parameter Summary Problems Arrays 2: Further Examples Varying the array size at run time Higher-dimension arrays A map Example 3: Sensible tabular output Example 4: Average of three sets of values Example 5: Booking arrangements in a theatre or cinema Additional forms of the DIMENSION attribute and DO loop statement Example 6: Voltage from 20 to +20 volts Example 7: Longitude from 180 to Notes The DO loop and straight repetition Example 8: Table of temperatures Example 9: Means and standard deviations Summary Problems Whole Array and Additional Array Features Terminology Rank Bounds Extent Size Shape Conformable Array element ordering Whole array manipulation Assignment Expressions Array sections Rank 1 array example Rank 2 array example Array constructors Rank 1 array example explicit values Rank 1 array example and implied DO loop Rank 1 array example and the DOT_PRODUCT intrinsic Rank 1 example with step size of 2 in implied DO loop

11 xii Contents Rank 1 array and the SUM intrinsic function Rank 2 arrays and the SUM intrinsic function Masked array assignment and the WHERE statement Notes The FORALL statement and FORALL construct Syntax Array element ordering and physical and virtual memory Summary Problems Bibliography Output of Results Integers I format or edit descriptor Reals F format or edit descriptor Metric and imperial conversion Overflow and underflow Reals E format or edit descriptor Simple E format example Spaces Characters A format or edit descriptor Headings Mixed type output in a FORMAT statement Common mistakes OPEN (and CLOSE) The OPEN statement Writing Repetition Some more examples Implied DO loops and array sections for array output Formatting for a line printer Mechanics of carriage control Generating a new line on both line printers and terminals Timing of writing formatted files Timing of writing unformatted files Summary Problems Reading in Data Reading from the terminal or keyboard versus reading from files Fixed fields on input Integers and the I format Reals and the F format Reals and the E Format

12 Contents xiii 13.3 Blanks, nulls and zeros Characters Skipping spaces and lines Reading File manipulation again Reading using array sections Timing of reading formatted files Timing of reading unformatted files Errors when reading Summary Problems Files Data files in Fortran Summary of options on OPEN More foolproof I/O Summary Problems Functions An introduction to predefined functions and their use Example 1: Simple function usage Generic functions Example 2: The ABS generic function Elemental functions Example 3: Elemental function use Transformational functions Example 4: Simple transformational use Example 5: Intrinsic DOT_PRODUCT use Notes on function usage Example 6: Easter Complete list of predefined functions Inquiry functions Transfer and conversion functions Computational functions Array functions Predefined subroutines Supplying your own functions Example 7: Simple user defined function An introduction to the scope of variables and local variables Recursive functions Example 8: Recursive factorial evaluation

13 xiv Contents Example 9: Recursive version of GCD Example 10: After removing recursion Pure functions Elemental functions Internal functions Example 11: Stirling's approximation Resumé Function syntax Rules and restrictions Problems Bibliography Recursion and problem solving Control Structures Selection among courses of action The BLOCK IF statement Example 1: Quadratic roots Note Example 2: Date calculation The CASE statement Example 3: Simple calculator Example 4: Counting vowels, consonants, etc The three forms of the DO statement Example 5: Sentinel usage CYCLE and EXIT Example 6: e**x evaluation Example 7: Wave breaking on an offshore reef Summary Control structure formal syntax Problems Bibliography Characters Character input Character operators Character substrings Character functions Collating sequence Summary Problems Complex Example Complex and kind type Summary

14 Contents xv 18.4 Problems Logical I/O Summary Problems User Defined Types Example 1: Dates Type definition Variable definition Example 2: Address lists Example 3: Nested user defined types Problems Bibliography An Introduction to Pointers Some basic pointer concepts The ASSOCIATED intrinsic function CVF 6.6C Intel, Windows, Lahey, Windows 5.70f NAG, Windows, Salford Referencing A and B before assignment CVF Intel, Windows Lahey, Windows 5.70f NAG, Windows Salford The NULL intrinsic Assignment via = Singly linked list Reading in an arbitrary quantity of numeric data Arrays of pointers Arrays of pointers and variable sized data sets Arrays of pointers and variable sized data sets Memory leak examples Nonstandard pointer examples Problems Introduction to Subroutines Example Defining a subroutine Referencing a subroutine

15 xvi Contents Dummy arguments or parameters and actual arguments Intent Local variables Local variables and the SAVE attribute Scope of variables Status of the action carried out in the subroutine Example Example 3 Quadratic example with interface blocks Example 4 Quadratic example and the CONTAINS statement Why bother? Summary Problems Subroutines: More on parameter passing Explicit-shape array Assumed-shape array Deferred-shape array Automatic arrays Assumed-size array Fortran 77 style Adjustable arrays Fortran 77 style Common code example Explicit-shape example Assumed-shape example Notes Characters arguments and assumed-length dummy arguments Rank 2 and higher arrays as parameters Explicit-shape dummy arrays Assumed-shape dummy array arguments Notes Using the intrinsic functions MATMUL and TRANSPOSE Automatic arrays and median calculation Internal subroutines and scope Timing the selection sort algorithm Timing Alternative median calculation algorithm Timing Recursive subroutines Quicksort Note Interface blocks Note Recursive subroutine Note Flexible design Note Timing information Summary

16 Contents xvii Problems Bibliography Commercial numerical and statistical subroutine libraries An Introduction to Modules Modules for global data Modules for precision specification and constant definition Note Modules for sharing arrays of data Modules for derived data types Person data type Modules containing procedures Quicksort example Modules containing procedures Statistics example The solution of linear equations using Gaussian elimination Notes Module for kind type Deferred-shape arrays Intrinisic functions MAXVAL and MAXLOC Notes on module usage and compilation Summary Problems Bibliography Converting from Fortran Deleted features Obsolescent features Arithmetic IF Real and double precision DO control variables Shared DO termination and non-enddo termination Alternate RETURN PAUSE statement ASSIGN and assigned GOTO statements Assigned FORMAT statements H editing Better alternatives Example Example Commercial conversion tools NAG Polyhedron Original Fortran Fortran 77 Version Fortran 90 Version Summary

17 xviii Contents 25.8 Problems Case Studies Using linked lists for sparse matrix problems Inner product of two sparse vectors Solving a system of first-order ordinary differential equations using Runga Kutta Merson Note: Alternative form of the ALLOCATE statement Note: Automatic arrays Note: Dummy procedure arguments Keyword and optional arguments Generic procedures A function that returns a variable length array Operator and assignment overloading A subroutine to extract the diagonal elements of a matrix Perfectly balanced tree Pure function example Pure constraints Elemental function example Elemental constraints Elemental subroutine example Date class Graphics example dislin Problems Bibliography ISO TR IEEE Arithmetic History IEEE 754 Specifications Single precision floating point format Double precision floating point format Two classes of extended floating point formats Accuracy requirements Base conversion Converting between decimal and binary floating point formats and vice versa Exception handling Rounding directions Rounding precisions Resumé ISO TR IEEE_FEATURES module IEEE_EXCEPTIONS module IEEE_ARITHMETIC module IEEE data type selection

18 Contents xix General support enquiry functions Rounding modes Number classification Arithmetic operations Summary Bibliography Web-based sources Hardware sources Operating Systems Java and IEEE C and IEEE ISO TR Allocatable Enhancements Allocatable dummy array example Allocatable function result example Allocatable structure component example Summary Problem Fortran 2003 and the Enhanced Module Facility Derived type enhancements Object oriented programming support Data manipulation enhancements Input/output enhancements Interoperability with the C programming language Procedure pointers Scoping enhancements Support for IEC (IEEE 754) exceptions and arithmetic Support for international usage: (ISO 10646) Enhanced integration with the host operating system The ASSOCIATE construct Enhanced modules facility Summary Parallel Programming MPI Co array Fortran Openmp PVM HPF Parallel programming and high-performance computing Summary Miscellaneous

19 xx Contents 31.1 Program development and software engineering Modules Programming style Programs should be easy to read Programming style Programs should behave well Data structures Algorithms Recursion Structured programming and the GOTO statement Efficiency, space-time trade-off Program testing Simple debugging techniques Software tools Cross referencing Pretty print NAGWare f90 Tools Numerical software sources Numerical Algorithms Group Visual Numerics Netlib Coda Bibliography: All sources (bar one) taken from comp.software-eng Software engineering Programming style Software testing Fun A Glossary B Sample Program Examples C ASCII Character Set D Intrinsic Functions and Procedures E English and Latin Texts F Coded Text Extract G Formal syntax H Compiler Options Index

INTRODUCING FORTRAN 90

INTRODUCING FORTRAN 90 Springer Berlin Heidelberg New Yorlc Barcelona Budapest HongKong London Milan Paris Tokyo Ian Chivers and Jane Sleightholme INTRODUCING FORTRAN 90, Springer Ian David Chivers, B.Sc.,