fortran lecture, slide

• 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

Jordan Martin Steven Devine

• 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

• 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.

Hello World

program hello

print *, "Hello World!"

end program hello

Current Usage

• Scientific Community

• Engineers

•Super Computing

• 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.

• Cons

– Case Insensitive

– Whitespace insensitive

– Many built-in functions and types, lacks high orthogonality

– GOTO

– Column major order for 2D arrays

• Pros

– Case insensitive

– Whitespace insensitive

– Powerful functions and algebraic evaluation

• Cons

– GOTO is the basis for control structure in older versions

– Names restricted to 6 characters

– Variables are in scope only for subroutines

- 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

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

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

-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

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;

}

}

- 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

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

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

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/