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Fortran: A Historic Programming Language for Engineering and Scientific Computing

Discover the history, syntax, data types, control statements, functions, and subroutines of Fortran, the first-ever High-Level Language designed by IBM in 1954-57. Explore concepts like arrays, control structures, functions, and subroutines that make Fortran suitable for scientific computation. Learn about the evolution of Fortran from the classic Fortran 77 to the modern Fortran 2000, featuring advanced features like dynamic allocation, recursive functions, and object orientation. Explore its current applications in cosmology, fusion research, and more, and its future potential for object orientation and interoperability with other languages.

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Fortran: A Historic Programming Language for Engineering and Scientific Computing

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  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(‘Don’’t’, ’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 = pi*r*r write (*,*) 'Area = ', area stop end

  9. DATA TYPES-III • Supports multiple assignments : • eg: data m,n/10,20/, x,y/2*2.5/ 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(0:19), REA: weird(-162:237) • Allows arrays of up to seven dimensions REAL a(3,5), REAL b(2,0:3) • 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((A+B)*2)100,200,300 • Logical if : IF(e)statement • Eg.IF(A.LT.0.)a=0.0 • 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 = 0.1*t * (m**2 + 14*m) 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. 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 CALL BY REFERENCE PARADIGM Fortran follows call by reference paradigm. Eg.

  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…. • Nasa’s 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.pdf • 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

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