FORTRAN

1
FORTRAN

• FORmula TRANslator
• -Anand Trivedi
  

2
HISTORY

• Designed and written from scratch in 1954-57 by
  an IBM team lead by John W. Backus as the first
  ever High Level Language
• Direct competition with assembler compelled it to
  have a fast, well optimized code

3
INTRODUCTION

• Fortran is a general purpose programming
  language, mainly intended for engineering
  scientific computation
• Browse over its most popular version Fortran
  77(in 1977)

4
LEXICAL ASPECTS

• Input format Formerly Punch cards
• Not a free format language
• Column position rules
• Col. 1 Blank, or a "c" or "" for
  comments
• Col. 2-5 Statement label (optional)
• Col. 6 Continuation of previous line
  (optional)
• Col. 7-72 Statements
• Col. 73-80 Sequence number (optional, rarely
  used today)
• Delimiters End of the line
• Blank space ignored
• Variable names of 1-6 characters (A-Z, 0-9). The
  first character must be a letter.

5
EXPRESSIONS

• Arithmetic Operators
• , /, , -,
• Relational Operators .LT., .LE., .GE., .GT.,
  .EQ., and .NE.
• Logical Operators .NOT., .AND., .OR., .EQV. ,
  .NEQV.
• eg logical a, b
• a .TRUE.
• b a .AND. 3 .LT. 5/2
• Arithmetic expressions are evaluated first, then
  relational operators, and finally logical
  operators

6
DATA TYPES-I

• Six data types are explicitly permitted
• INTEGER (0,25,25,-25)
• REAL (-1.5,3E5, .123E-3)
• DOUBLE PRECISION (1D2, 6.89D-8)
• COMPLEX ((-10,5), (.4E2,-.31E-1)
• LOGICAL(.TRUE., .FALSE.)
• CHARACTER(Dont, A1 PLC/)

7
DATA TYPES-II

• Each variable has to be declared explicitly
• Implicit rule All variables starting with the
  letters i-n are integers and all others are real
• CONSTANT By using PARAMETER statement
• eg. parameter (pi 3.14159)

8
SAMPLE EXAMPLE- I

• 1234567890123456789012345678901234567890
• program circle
• real r, area
• pi parameter (pi 3.14159)
• C write read statements for I/p O/p
• write (,) 'Give radius r'
• read (,) r
• area pirr
• write (,) 'Area ', area
• stop
• end

9
DATA TYPES-III

• Supports multiple assignments
• eg data m,n/10,20/, x,y/22.5/
• or
• data m/10/, n/20/, x/2.5/, y/2.5/

10
DATA TYPES ARRAYS

• The only complex data structure
• Index starts from 1 onwards
• INTEGER i(10) , REAL
  a(12), REAL b()
• However these are also valid
• REAL b(019), REA
  weird(-162237)
• Allows arrays of up to seven dimensions
• REAL a(3,5), REAL
  b(2,03)
• By default values are not Zero.
• Array values are not checked before being used.
  

11
CONTROL STATEMENTS-I

• GOTO statement GOTO label
• IF statement
• Arithmetic if IF (e)s1,s2,s3
• Eg. IF((AB)2)100,200,300
• Logical if IF(e)statement
• Eg.IF(A.LT.0.)a0.0
• IF-THEN-ELSE Statement
• If (e) THEN statements
• Else statements
• END IF
• Nested IF allowed

12
CONTROL STATEMENTS-II

• CONTINUE
• Just one type of loop DO loop
• eg integer i, n, sum
• n 10
• DO 10 i 0, n,2
• write(,) 'i ', i
• 10 CONTINUE
• No recursion (static allocation)

13
FUNCTIONS

• Inbuilt functions like abs, sin, cos etc
• Define own functions
• real function r(m,t)
• real t,m
• r 0.1t (m2 14m)
• if (r .LT. 0) r 0.0
• return
• end

14
SUBROUTINES

• Makes language modular
• No global variables. So subroutines helps to pass
  it. Eg
• subroutine iswap (a, b)
• integer a, b
• c Local variables
• integer tmp 
• tmp a
• a b
• b tmp 
• return
• end

15
CALL BY REFERENCE PARADIGM
Fortran follows call by reference paradigm. Eg.

• program callex
• integer m, n
• m 1
• n 2  
• call iswap(m, n)
• write(,) m, n 
• stop
• end

• subroutine iswap (a, b)
• integer a, b
• c Local variables
• integer tmp 
• tmp a
• a b
• b tmp 
• return
• end

16
FORMAT STATEMENT

• Used for particular input or output format
• The most common format code letters are
• A - text string
• D - double precision numbers, exponent notation
• E - real numbers, exponent notation
• F - real numbers, fixed point format
• I - integer
• X - horizontal skip (space)
• / - vertical skip (newline)

17
THINGS NOT COVERED

• Input and Output concepts
• Input and Output statements
• (READ, WRITE, PRINT, OPEN,CLOSE,INQUIRE..)
• Format specifications
• (Numeric editing, Logical editing, Character
  editing..)

18
PRESENT APPLICATIONS

• Cosmology, fusion research, surface physics,
  molecular dynamics.
• Nasas Anisotropy probe (flown in 2000) used some
  legacy f-77 though mostly f-90
• US geological survey still uses f-77!...

19
PRESENT FUTURE

• F-90 has free format, dynamic allocation and
  pointers, user defined data type, modules,
  recursive functions, built-in arrays operator
  overloading.
• Fortran 2000 (delayed to 2004) hopes to have
  object orientation, interoperability with C,
  asynchronous I/o and lot more

20
REFERENCES

• http//personal.cfw.com/terry2/tutorial
• http//www.ibiblio.org/pub/languages/fortran/unfp.
  html
• http//physics.weber.edu/ostlie/phsx2300/future.pd
  f
• http//macams1.bo.infn.it/tutorial/format.html
• http//sunsite.univalle.edu.co/fortran/ch2-3.html
• Fortran-77
• - Harry Katzan
• Structured Fortran77 Programming
• - Seymour Pollack