Introduction to Fortran 90 Programming

1
Introduction to Fortran 90 Programming
André Paul
2
Reading

• The following notes are based on
• Ellis, T.M.R., Phillips, Ivor R., and Lahey,
  Thomas M. Fortran 90 Programming, Addison-Wesley
  Publishing Company.

3
Telling a Computer What To Do

• To get a computer to perform a specific task it
  must be given a sequence of unambiguous
  instructions or a program.
• Generating a program
• Text file with instructions (Source Code
  Fortran 90)
• Translation into computer-compatible form
  (Compiler)
• Executable Program

4
The Linux look and feel

• Cygwin is a Linux-like environment for Windows
  that consists of two parts
• A DLL (Dynamic Link Library, cygwin1.dll)
• A collection of tools, which provide Linux look
  and feel
• Link http//www.cygwin.com

5
A few useful Linux commands

• pwd print name of current/working directory
• ls list directory contents
• cd change directory
• mkdir make directories
• rm remove files or diretories
• man format and display the on-line manual pages
  (e.g. man pwd)

6
How to start cygwin

• Open cygwin window by double-clicking on the
  start_cygwin DOS batchfile provided with this
  exercise
• If this does not work ...

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How to start cygwin II

• Double-click on the cygwin icon on the desktop
• In the computer room, try typing cd "ceida"
• If this does not work ...

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How to get to your directory

• Copy the file /dozent/public/Austausch/anma/.profi
  le to your cygwin home directory

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How to get to your directory II

• Try it the long way
• cd c
• cd Dokumente und Einstellungen
• cd put your username here
• cd Eigene Dateien
• cd put your working directory here

10
Creating and Running a Program

• Invoke the editor from the Start menu, or type

into the cygwin window to create a file called
hello.f90.
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Creating and Running a Program

• Use the editor to create a file called hello.f90,
  which contains the following source code
• Compile by typing g95 hello.f90 (in the cygwin
  window)
• Run the program by typing ./a.exe (g95 by default
  creates an executable called a.exe)

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Basic Fortran 90 concepts

• All words which have a special meaning in Fortran
  are known as keywords.
• Every main program unit must start with a PROGRAM
  statement which consists of the word PROGRAM
  followed by the name of the program as given by
  the programmer.

13
Avoid implicit declaration

• The special IMPLICIT NONE statement should always
  be placed immediately after the PROGRAM
  statement. It instructs the compiler that all
  variables must be declared before use.

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Basic building blocks

• A main program unit

15
REAL and INTEGER variables

• Use the INTEGER name statement to declare a
  whole-number variable
• Use the REAL name statement to declare a
  floating-point variable

16
Repeating parts of your program
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Using files to preserve data

• Connecting external files to your program
• Connect a file to a unit by OPEN(UNITunit_number
  ,FILEfile_name), where unit_number is an integer
  number, variable or parameter and file_name is a
  character expression.

18

• Write a record to a file by WRITE
  (UNITunit_number,FMT)
• Disconnect a file from a unit by means of a CLOSE
  (UNITunit_number) statement

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Introduction to arrays
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Parameterized REAL variables

• REAL variables (floating point numbers) are
  parameterized
• The kind type parameter specifies minimum
  precision and exponent range requirements.

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• ! Parameter declarations
• ! Symbolic name for a real kind type with at
  least
• ! 15 decimal digits of precision and an exponent
  range
• ! from 10300 to 10(-300) (double precision)
• INTEGER, PARAMETER dpSELECTED_REAL_KIND(P15,R
  300)
• ! Symbolic name for a real kind type with at
  least
• ! 6 decimal digits of precision and an exponent
  range
• ! from 1030 to 10(-30) (single precision)
• INTEGER, PARAMETER spSELECTED_REAL_KIND(P6,R
  30)
• ! Symbolic name for a default real kind type
• INTEGER, PARAMETER qdp
• ! Variable declarations
• REAL(KINDq) dpress
• REAL(KINDq), DIMENSION(1km) p

22
Functions and subroutines
REAL(KINDq) FUNCTION feuler(y,s,dx)
IMPLICIT NONE !-----------------------------
------------------------------------ ! This
function integrates one time step using the
forward Euler ! method for the ODE dy/dx
f(x,y(x)) ! ! Input arguments
! y temperature (K) ! s solar
radiation (W m(-2)) ! dx time step
(s) ! ! Result variable !
feuler dy ! ! Uses external
function rhs ! ! Based on code by M.
Yoshimori !---------------------------------
--------------------------------
REAL(KINDq), INTENT(IN) y,s,dx feuler
rhs(y,s)dx END FUNCTION feuler
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The block IF construct

• ! Variable declarations
• ! tol criteria of convergence (K)
• REAL(KINDq) tol
• ..
• ! Initializations
• tol 1.0E-03_q
• ..
• ! Time loop
• DO itt1,ittmax
• ..
• ! Test for convergence
• IF (ABS(tf ti) lt tol) THEN
• EXIT
• END IF
• END DO