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Fortran

Fortran. Jordan Martin Steven Devine. Background. Developed by IBM in the 1950s Designed for use in scientific and engineering fields Originally written as FORTRAN Convention is caps up to FORTRAN77 Title caps for Fortran 90 forward. Background.

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Fortran

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  1. Fortran Jordan Martin Steven Devine

  2. Background • Developed by IBM in the 1950s • Designed for use in scientific and engineering fields • Originally written as FORTRAN • Convention is caps up to FORTRAN77 • Title caps for Fortran 90 forward

  3. Background • Brainchild of John Backus as a more friendly and useable alternative to assembly language • Fortran’s compiler, released in 1957, was the first optimizing compiler.

  4. Hello World program hello print *, "Hello World!" end program hello

  5. Current Usage • Scientific Community • Engineers • Super Computing

  6. Readability • Pros • Formulas and functions are easily recognizable • Strongly typed. • Looping and control statements work in familiar ways in later versions of Fortran, using do as the primary key word.

  7. Readability • Cons • Case Insensitive • Whitespace insensitive • Many built-in functions and types, lacks high orthogonality • GOTO • Column major order for 2D arrays

  8. Writeability • Pros • Case insensitive • Whitespace insensitive • Powerful functions and algebraic evaluation

  9. Writeability • Cons • GOTO is the basis for control structure in older versions • Names restricted to 6 characters • Variables are in scope only for subroutines

  10. Reliability - The FORTRAN language has not specified evaluation order for expressions - Compilers are free to evaluate each line as they please PROGRAM ARGORD INTEGER I, F1, F2, F3, F4 EXTERNAL F1, F2, F3, F4 WRITE (*,*) 'Evaluation order: ' I = F1(I) + F2(I) + F3(I) + F4(I) END

  11. Short Circuit Evaluation • The compiler is free to evaluate boolean expressions in any order, • making short-circuit evaluation unreliable • This code will either work as intended or crash, depending on the • compiler that was used • INTEGER I • REAL ARRAY(100) • ........................... • IF ((I .GE. 1) .AND. (I .LE. 100) .AND. ARRAY(I) .GT. 0) THEN • WRITE (*,*) 'Array element is positive ' • ENDIF

  12. Strong Type Checking • - FORTRAN uses static (compile time) type checking • At run time all variables in memory are bit strings without • data type information • No type checking is done at run time, variables are just • accessed by the starting address of variable

  13. Portability • FORTRAN revisions are almost completely backwards-compatible and • have only removed obsolete instructions • FORTRAN 90 introduced KIND type parameters, which are • variables can be declared with arbitrarily specified ranges and • precisions, eliminating platform-based data type issues • -An example of the KIND type: • real (kind=kind(0.0)) r • kind(0.0) defaults to the processor's built in size for a real, • or the programmer can specify the number of digits

  14. FORTRAN Exception Handling - In FORTRAN, pointers cannot overlap in memory - This is done to allow optimization for greater speed in numerical calculations - All arrays passed to subroutines are guaranteed not to be aliased, so array elements can be stored in registers for the duration of the subroutine void transform (float *output, float * input, float * matrix, int n) { int i; for (i=0; i<n; i++) { float x = input[i*2+0]; float y = input[i*2+1]; output[i*2+0] = matrix[0] * x + matrix[1] * y; output[i*2+1] = matrix[2] * x + matrix[3] * y; } }

  15. Cost • - Time spent learning a dying niche language • There are free compilers available that vary in quality and output. • The expensive compilers offer tools and integration into modern programs • like .NET • Legacy FORTRAN code can be difficult to read and refactor due to age. • Older FORTRAN programs may not have obeyed any recognizable • methodology. Also, GOTO statements.

  16. Modern Uses • - A majority of supercomputers run programs written in FORTRAN • Monster.com lists about fifty jobs that require FORTRAN experience. • Twenty of those fifty also require security clearance. • FORTRAN is still the fastest when it comes to computationally- • intensive mathematical models, such as weather prediction, • computational science, air and fluid modeling, etc.

  17. Parting Thoughts • FORTRAN isn't unique. Everything FORTRAN does can also be done • by more powerful languages, starting with C • - FORTRAN is fast with mathematics, but Moore's Law is faster • FORTRAN was an important step in programming languages, • but it now only caters to the niche market of High Performance Computing.

  18. Sources http://www.ibiblio.org/pub/languages/fortran/ch1-8.html http://www.lahey.com/lookat90.htm http://chronicle.com/blogs/wiredcampus/supercomputers-often-run-outdated-software/8184 http://en.wikipedia.org/wiki/Row-major_order http://fortran.com/

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