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Fortran Jordan Martin Steven Devine. Background Developed by IBM in the 1950s Designed for use in scientific and engineering fields Originally written.

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Presentation on theme: "Fortran Jordan Martin Steven Devine. Background Developed by IBM in the 1950s Designed for use in scientific and engineering fields Originally written."— Presentation transcript:

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 INTEGERI, F1, F2, F3, F4 EXTERNALF1, 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

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 chronicle.com/blogs/wiredcampus/supercomputers-often-run-outdated-software/8184


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