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Fortran (; formerly FORTRAN) is a general-purpose,
compiled In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...
imperative Imperative may refer to: *Imperative mood, a grammatical mood (or mode) expressing commands, direct requests, and prohibitions *Imperative programming, a programming paradigm in computer science *Imperative logic *Imperative (film), ''Imperative'' ...
programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science) ...

programming language
that is especially suited to numeric computation and
scientific computing Computational science, also known as scientific computing or scientific computation (SC), is a field that uses advanced computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes ...
. Fortran was originally developed by
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
in the 1950s for scientific and engineering applications, and subsequently came to dominate scientific computing. It has been in use for over six decades in computationally intensive areas such as
numerical weather prediction#REDIRECT Numerical weather prediction {{Redirect category shell, 1= {{R from other capitalisation ...
,
finite element analysis The finite element method (FEM) is a widely used method for numerically solving differential equations arising in engineering and mathematical modeling. Typical problem areas of interest include the traditional fields of structural analysis, ...
,
computational fluid dynamics#REDIRECT Computational fluid dynamics Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid dynamics, fluid flows. Computers are used ...
,
geophysics Geophysics () is a subject of natural science Natural science is a branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a b ...

geophysics
,
computational physics Computational physics is the study and implementation of numerical analysis to solve problems in physics for which a Scientific theory, quantitative theory already exists. Historically, computational physics was the first application of modern comp ...
,
crystallography Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids (see crystal structure). The word "crystallography" is derived from the Greek language, Greek words ''crystallon'' "cold drop, frozen drop" ...

crystallography
and
computational chemistry Computational chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior a ...
. It is a popular language for
high-performance computing A supercomputer is a computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known a ...
and is used for programs that benchmark and rank the world's fastest supercomputers. Fortran has had numerous versions, each of which has added extensions while largely retaining compatibility with preceding versions. Successive versions have added support for
structured programming Structured programming is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with impl ...
and processing of character-based data (FORTRAN 77),
array programming In computer science, array programming refers to solutions which allow the application of operations to an entire set of values at once. Such solutions are commonly used in computational science, scientific and engineering settings. Modern progra ...
,
modular programming Modular programming is a software design Software design is the process by which an Agency (philosophy), agent creates a specification of a Artifact (software development), software artifact intended to accomplish goals, using a set of primit ...
and
generic programming Generic programming is a style of computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming invol ...
(Fortran 90), high performance Fortran (Fortran 95),
object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mai ...
(Fortran 2003),
concurrent programming Concurrency, concurrent, or concurrence may refer to: * Concurrence, in jurisprudence, the need to prove both ''actus reus'' and ''mens rea'' * Concurring opinion (also called a "concurrence"), a legal opinion which supports the conclusion, though ...
(Fortran 2008), and native
parallel computing Parallel computing is a type of computation Computation is any type of that includes both al and non-arithmetical steps and which follows a well-defined model (e.g. an ). Mechanical or electronic devices (or, , people) that perform computat ...
capabilities (Coarray Fortran 2008/2018). Fortran's design was the basis for many other programming languages. Among the better-known is
BASIC BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the ar ...

BASIC
, which is based on FORTRAN II with a number of
syntax In linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as well as the ...
cleanups, notably better logical structures, and other changes to work more easily in an interactive environment. Fortran was ranked 13 in the
TIOBE index The TIOBE programming community index is a measure of popularity of programming languages, created and maintained by the TIOBE Software BV based in Eindhoven, the Netherlands The Netherlands ( nl, Nederland ), informally referred to as Hollan ...
, a measure of the popularity of programming languages, climbing 29 positions from its ranking of 42 in August 2020.


Naming

The name FORTRAN is derived from ''Formula Translating System'', ''Formula Translator,'' ''Formula Translation'', or ''Formulaic Translation.'' The names of earlier versions of the language through FORTRAN 77 were conventionally spelled in all-uppercase (FORTRAN 77 was the last version in which the Fortran character set included only uppercase letters). The official language
standards Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined relationship to a unit of ...
for Fortran have referred to the language as "Fortran" with initial caps (rather than "FORTRAN" in all-uppercase) since Fortran 90.


Origins

In late 1953, submitted a proposal to his superiors at
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
to develop a more practical alternative to
assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gene ...
for programming their
IBM 704 The IBM 704, introduced by IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founde ...
mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform gener ...
.
https://archive.org/details/history-of-fortran]
Backus' historic FORTRAN team consisted of programmers Richard Goldberg, Sheldon F. Best, Harlan Herrick, Peter Sheridan, Roy Nutt, Robert Nelson, Irving Ziller, Harold Stern,
Lois Haibt Lois Mitchell Haibt (born 1934) is an American computer scientist best known for being a member of the ten-person team at IBM that developed Fortran, FORTRAN, the first successful high-level programming language. She is known as an early pioneer i ...
, and
David Sayre David Sayre (March 2, 1924 – February 23, 2012) was an American scientist, credited with the early development of direct methods (crystallography), direct methods for X-ray crystallography#Protein crystallography, protein crystallography and of ...
. Its concepts included easier entry of equations into a computer, an idea developed by
J. Halcombe Laning J. Halcombe "Hal" Laning Jr. (February 14, 1920 in Kansas City, Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Wi ...

J. Halcombe Laning
and demonstrated in the
Laning and Zierler system The Laning and Zierler system (sometimes called "George" by its users) was one of the first operating algebraic compilers, that is, a system capable of accepting mathematical formulas in Infix notation, algebraic notation and producing equivalent ma ...
of 1952. A draft specification for ''The IBM Mathematical Formula Translating System'' was completed by November 1954. The first manual for FORTRAN appeared in October 1956, with the first FORTRAN
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
delivered in April 1957. This was the first
optimizing compiler In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest commo ...
, because customers were reluctant to use a
high-level programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , , ...
unless its compiler could generate code with performance approaching that of hand-coded assembly language. While the community was skeptical that this new method could possibly outperform hand-coding, it reduced the number of programming
statements Statement or statements may refer to: Common uses *Statement (computer science)In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to ...
necessary to operate a machine by a factor of 20, and quickly gained acceptance. John Backus said during a 1979 interview with ''Think'', the IBM employee magazine, "Much of my work has come from being lazy. I didn't like writing programs, and so, when I was working on the
IBM 701 The IBM 701 Electronic Data Processing Machine, known as the Defense Calculator while in development, was IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New ...
, writing programs for computing missile trajectories, I started work on a programming system to make it easier to write programs." The language was widely adopted by scientists for writing numerically intensive programs, which encouraged compiler writers to produce compilers that could generate faster and more efficient code. The inclusion of a complex number data type in the language made Fortran especially suited to technical applications such as electrical engineering. By 1960, versions of FORTRAN were available for the
IBM 709 The IBM 709 was a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. ...
,
650 __NOTOC__ Year 650 (Roman numerals, DCL) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. The denomination 650 for this year has been used since the early medieval period, when the Anno Domini ca ...
,
1620 Events January–June * February 4 This day marks the approximate midpoint of winter in the Northern Hemisphere and of summer in the Southern Hemisphere (starting the season at the December solstice). Events Pre–1600 *211 ...

1620
, and 7090 computers. Significantly, the increasing popularity of FORTRAN spurred competing computer manufacturers to provide FORTRAN compilers for their machines, so that by 1963 over 40 FORTRAN compilers existed. For these reasons, FORTRAN is considered to be the first widely used
cross-platform In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and soft ...
programming language. The development of Fortran paralleled the early evolution of compiler technology, and many advances in the theory and design of
compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily ...

compiler
s were specifically motivated by the need to generate efficient code for Fortran programs.


FORTRAN

The initial release of FORTRAN for the IBM 704 contained 32
statements Statement or statements may refer to: Common uses *Statement (computer science)In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to ...
, including: * and statements * Assignment statements * Three-way ''arithmetic'' statement, which passed control to one of three locations in the program depending on whether the result of the arithmetic statement was negative, zero, or positive * statements for checking exceptions (, , and ); and statements for manipulating * , computed , , and assigned * loops * Formatted I/O: , , , , , , and * Unformatted I/O: , , , and * Other I/O: , , and * , , and * statement (for providing
optimization File:Nelder-Mead Simionescu.gif, Nelder-Mead minimum search of Test functions for optimization, Simionescu's function. Simplex vertices are ordered by their values, with 1 having the lowest ( best) value., alt= Mathematical optimization (alter ...
hints to the compiler). The arithmetic statement was reminiscent of (but not readily implementable by) a three-way comparison instruction (CAS—Compare Accumulator with Storage) available on the 704. The statement provided the only way to compare numbers—by testing their difference, with an attendant risk of overflow. This deficiency was later overcome by "logical" facilities introduced in FORTRAN IV. The statement was used originally (and optionally) to give branch probabilities for the three branch cases of the arithmetic IF statement. The first FORTRAN compiler used this weighting to perform ''at compile time'' a
Monte Carlo simulation Monte Carlo methods, or Monte Carlo experiments, are a broad class of computation Computation is any type of calculation A calculation is a deliberate process that transforms one or more inputs into one or more results. The term is used in a v ...
of the generated code, the results of which were used to optimize the placement of basic blocks in memory—a very sophisticated optimization for its time. The Monte Carlo technique is documented in Backus et al.'s paper on this original implementation, ''The FORTRAN Automatic Coding System'':
The fundamental unit of program is the
basic block In compiler construction, a basic block is a straight-line code sequence with no branches in except to the entry and no branches out except at the exit. This restricted form makes a basic block highly amenable to analysis. Compiler In computin ...
; a basic block is a stretch of program which has one entry point and one exit point. The purpose of section 4 is to prepare for section 5 a table of predecessors (PRED table) which enumerates the basic blocks and lists for every basic block each of the basic blocks which can be its immediate predecessor in flow, together with the absolute frequency of each such basic block link. This table is obtained by running the program once in Monte-Carlo fashion, in which the outcome of conditional transfers arising out of IF-type statements and computed GO TO's is determined by a random number generator suitably weighted according to whatever FREQUENCY statements have been provided.
Many years later, the statement had no effect on the code, and was treated as a comment statement, since the compilers no longer did this kind of compile-time simulation. A similar fate has befallen ''compiler hints'' in several other programming languages, e.g. the keyword in C. The first FORTRAN compiler reported diagnostic information by halting the program when an error was found and outputting an error code on its console. That code could be looked up by the programmer in an error messages table in the operator's manual, providing them with a brief description of the problem. Later, an error-handling subroutine to handle user errors such as division by zero, developed by NASA, was incorporated, informing users of which line of code contained the error.


Fixed layout and punched cards

Before the development of disk files, text editors and terminals, programs were most often entered on a
keypunch A keypunch is a device for precisely punching holes into stiff paper cards at specific locations as determined by keys struck by a human operator. Other devices included here for that same function include the gang punch, the pantograph punch, a ...
keyboard onto 80-column
punched card A punched card (also punch cardSteven Pinker, in ''The Stuff of Thought'', Viking, 2007, p.362, notes the loss of ''-ed'' in pronunciation ''as it did in ice cream, mincemeat, and box set, formerly iced cream, minced meat, and boxed set.'' or p ...

punched card
s, one line to a card. The resulting deck of cards would be fed into a card reader to be compiled. Punched card codes included no lower-case letters or many special characters, and special versions of the IBM 026
keypunch A keypunch is a device for precisely punching holes into stiff paper cards at specific locations as determined by keys struck by a human operator. Other devices included here for that same function include the gang punch, the pantograph punch, a ...
were offered that would correctly print the re-purposed special characters used in FORTRAN. Reflecting punched card input practice, Fortran programs were originally written in a fixed-column format, with the first 72 columns read into twelve 36-bit words. A letter "C" in column 1 caused the entire card to be treated as a comment and ignored by the compiler. Otherwise, the columns of the card were divided into four fields: * 1 to 5 were the label field: a sequence of digits here was taken as a label for use in DO or control statements such as GO TO and IF, or to identify a FORMAT statement referred to in a WRITE or READ statement. Leading zeros are ignored and 0 is not a valid label number. * 6 was a continuation field: a character other than a blank or a zero here caused the card to be taken as a continuation of the statement on the prior card. The continuation cards were usually numbered 1, 2, ''etc.'' and the starting card might therefore have zero in its continuation column—which is not a continuation of its preceding card. * 7 to 72 served as the statement field. * 73 to 80 were ignored (the IBM 704's
card reader A card reader is a data input device that reads data from a card-shaped storage medium On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data storage medium. Data Data (; ...
only used 72 columns). Columns 73 to 80 could therefore be used for identification information, such as punching a sequence number or text, which could be used to re-order cards if a stack of cards was dropped; though in practice this was reserved for stable, production programs. An
IBM 519The IBM 519 Document-Originating Machine, introduced in 1946, was the last in a series of unit record machines designed for automated preparation of punched card A punched card (also punch cardSteven Pinker, in ''The Stuff of Thought'', Viking, ...
could be used to copy a program deck and add sequence numbers. Some early compilers, e.g., the IBM 650's, had additional restrictions due to limitations on their card readers.
Keypunch A keypunch is a device for precisely punching holes into stiff paper cards at specific locations as determined by keys struck by a human operator. Other devices included here for that same function include the gang punch, the pantograph punch, a ...
es could be programmed to tab to column 7 and skip out after column 72. Later compilers relaxed most fixed-format restrictions, and the requirement was eliminated in the Fortran 90 standard. Within the statement field,
whitespace character In computer programming, whitespace is any character (computing), character or series of characters that represent horizontal or vertical space (punctuation), space in typography. When rendered, a whitespace character does not correspond to a visi ...
s (blanks) were ignored outside a text literal. This allowed omitting spaces between tokens for brevity or including spaces within identifiers for clarity. For example, was a valid identifier, equivalent to , and 101010DO101I=1,101 was a valid statement, equivalent to 10101 DO 101 I = 1, 101 because the zero in column 6 is treated as if it were a space (!), while 101010DO101I=1.101 was instead 10101 DO101I = 1.101, the assignment of 1.101 to a variable called DO101I. Note the slight visual difference between a comma and a period. Hollerith strings, originally allowed only in FORMAT and DATA statements, were prefixed by a character count and the letter H (e.g., ), allowing blanks to be retained within the character string. Miscounts were a problem.


Evolution


FORTRAN II

IBM's ''FORTRAN II'' appeared in 1958. The main enhancement was to support
procedural programming Procedural programming is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with i ...
by allowing user-written subroutines and functions which returned values with parameters passed by
reference Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a ''name ...
. The COMMON statement provided a way for subroutines to access common (or
global Global means of or referring to a globe A globe is a spherical physical model, model of Earth, of some other astronomical object, celestial body, or of the celestial sphere. Globes serve purposes similar to maps, but unlike maps, they do not dis ...
) variables. Six new statements were introduced: * , , and * and * Over the next few years, FORTRAN II would also add support for the and data types. Early FORTRAN compilers supported no
recursion Recursion (adjective: ''recursive'') occurs when a thing is defined in terms of itself or of its type. Recursion is used in a variety of disciplines ranging from linguistics Linguistics is the scientific study of language, meaning tha ...
in subroutines. Early computer architectures supported no concept of a stack, and when they did directly support subroutine calls, the return location was often stored in one fixed location adjacent to the subroutine code (e.g. the
IBM 1130 The IBM 1130 Computing System, introduced in 1965, was IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The co ...
) or a specific machine register (
IBM 360 The IBM System/360 (S/360) is a family of mainframe computer A pair of IBM mainframes. On the left is the IBM z Systems z13. On the right is the IBM LinuxONE Rockhopper.">IBM_LinuxONE.html" ;"title="IBM z Systems z13. On the right is the ...
''et seq''), which only allows recursion if a stack is maintained by software and the return address is stored on the stack before the call is made and restored after the call returns. Although not specified in FORTRAN 77, many F77 compilers supported recursion as an option, and the Burroughs mainframes, designed with recursion built-in, did so by default. It became a standard in Fortran 90 via the new keyword RECURSIVE.


Simple FORTRAN II program

This program, for
Heron's formula In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space ...

Heron's formula
, reads data on a tape reel containing three 5-digit integers A, B, and C as input. There are no "type" declarations available: variables whose name starts with I, J, K, L, M, or N are "fixed-point" (i.e. integers), otherwise floating-point. Since integers are to be processed in this example, the names of the variables start with the letter "I". The name of a variable must start with a letter and can continue with both letters and digits, up to a limit of six characters in FORTRAN II. If A, B, and C cannot represent the sides of a triangle in plane geometry, then the program's execution will end with an error code of "STOP 1". Otherwise, an output line will be printed showing the input values for A, B, and C, followed by the computed AREA of the triangle as a floating-point number occupying ten spaces along the line of output and showing 2 digits after the decimal point, the .2 in F10.2 of the FORMAT statement with label 601. C AREA OF A TRIANGLE WITH A STANDARD SQUARE ROOT FUNCTION C INPUT - TAPE READER UNIT 5, INTEGER INPUT C OUTPUT - LINE PRINTER UNIT 6, REAL OUTPUT C INPUT ERROR DISPLAY ERROR OUTPUT CODE 1 IN JOB CONTROL LISTING READ INPUT TAPE 5, 501, IA, IB, IC 501 FORMAT (3I5) C IA, IB, AND IC MAY NOT BE NEGATIVE OR ZERO C FURTHERMORE, THE SUM OF TWO SIDES OF A TRIANGLE C MUST BE GREATER THAN THE THIRD SIDE, SO WE CHECK FOR THAT, TOO IF (IA) 777, 777, 701 701 IF (IB) 777, 777, 702 702 IF (IC) 777, 777, 703 703 IF (IA+IB-IC) 777, 777, 704 704 IF (IA+IC-IB) 777, 777, 705 705 IF (IB+IC-IA) 777, 777, 799 777 STOP 1 C USING HERON'S FORMULA WE CALCULATE THE C AREA OF THE TRIANGLE 799 S = FLOATF (IA + IB + IC) / 2.0 AREA = SQRTF( S * (S - FLOATF(IA)) * (S - FLOATF(IB)) * + (S - FLOATF(IC))) WRITE OUTPUT TAPE 6, 601, IA, IB, IC, AREA 601 FORMAT (4H A= ,I5,5H B= ,I5,5H C= ,I5,8H AREA= ,F10.2, + 13H SQUARE UNITS) STOP END


FORTRAN III

IBM also developed a ''FORTRAN III'' in 1958 that allowed for
inline assemblyIn computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves tasks such as: analysis, generatin ...
code among other features; however, this version was never released as a product. Like the 704 FORTRAN and FORTRAN II, FORTRAN III included machine-dependent features that made code written in it unportable from machine to machine. Early versions of FORTRAN provided by other vendors suffered from the same disadvantage.


IBM 1401 FORTRAN

FORTRAN was provided for the
IBM 1401 The IBM 1401 is a variable-wordlength decimal computer Decimal computers are computers which can represent numbers and addresses in decimal The decimal numeral system A numeral system (or system of numeration) is a writing system ...
computer by an innovative 63-phase compiler that ran entirely in its
core memory Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this part of the body, and lack of core muscular de ...
of only 8000 (six-bit) characters. The compiler could be run from tape, or from a 2200-card deck; it used no further tape or disk storage. It kept the program in memory and loaded overlays that gradually transformed it, in place, into executable form, as described by Haines. This article was reprinted, edited, in both editions of ''Anatomy of a Compiler'' and in the IBM manual "Fortran Specifications and Operating Procedures, IBM 1401". The executable form was not entirely
machine language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, ...
; rather, floating-point arithmetic, sub-scripting, input/output, and function references were interpreted, preceding
UCSD Pascal UCSD Pascal is a Pascal programming language Pascal is an imperative and procedural programming language A programming language is a formal language comprising a Instruction set architecture, set of instructions that produce various kinds ...
P-code Bytecode, also termed portable code or p-code, is a form of instruction set In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practi ...
by two decades. IBM later provided a FORTRAN IV compiler for the 1400 series of computers.


FORTRAN IV

IBM began development of FORTRAN IV starting in 1961, as a result of customer demands. ''FORTRAN IV'' removed the machine-dependent features of FORTRAN II (such as ), while adding new features such as a data type, logical
Boolean expression In computer science, a Boolean expression is an Expression (programming), expression used in programming languages that produces a Boolean value when evaluated. A Boolean value is either true or false. A Boolean expression may be composed of a combi ...
s and the ''logical IF statement'' as an alternative to the ''arithmetic IF statement.'' FORTRAN IV was eventually released in 1962, first for the
IBM 7030 The IBM 7030, also known as Stretch, was IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in ...
("Stretch") computer, followed by versions for the
IBM 7090 The IBM 7090 is a second-generation transistorized upright=1.4, gate A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road A road is a thoroughfare, route, or way ...
,
IBM 7094 The IBM 7090 is a second-generation transistorized upright=1.4, gate A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road A road is a thoroughfare, route, or way ...
, and later for the
IBM 1401 The IBM 1401 is a variable-wordlength decimal computer Decimal computers are computers which can represent numbers and addresses in decimal The decimal numeral system A numeral system (or system of numeration) is a writing system ...
in 1966. By 1965, FORTRAN IV was supposed to be compliant with the ''standard'' being developed by the
American Standards Association The American National Standards Institute (ANSI ) is a private non-profit organization A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organize ...
X3.4.3 FORTRAN Working Group. Between 1966 and 1968, IBM offered several FORTRAN IV compilers for its
System/360 The IBM System/360 (S/360) is a family of mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for t ...
, each named by letters that indicated the minimum amount of memory the compiler needed to run. The letters (F, G, H) matched the codes used with System/360 model numbers to indicate memory size, each letter increment being a factor of two larger: * 1966 : FORTRAN IV F for DOS/360 (64K bytes) * 1966 : FORTRAN IV G for OS/360 (128K bytes) * 1968 : FORTRAN IV H for OS/360 (256K bytes) At about this time FORTRAN IV had started to become an important educational tool and implementations such as the University of Waterloo's WATFOR and
WATFIV WATFIV, or WATerloo FORTRAN IV, developed at the University of Waterloo The University of Waterloo (commonly referred to as Waterloo, UW, or UWaterloo) is a public university, public research university with a main campus in Waterloo, Ontario, C ...
were created to simplify the complex compile and link processes of earlier compilers.


FORTRAN 66

Perhaps the most significant development in the early history of FORTRAN was the decision by the ''American Standards Association'' (now
American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of Standardization, voluntary consensus standards for products, services, processes, systems, and personnel in the United Sta ...
(ANSI)) to form a committee sponsored by BEMA, the Business Equipment Manufacturers Association, to develop an ''American Standard Fortran''. The resulting two standards, approved in March 1966, defined two languages, ''FORTRAN'' (based on FORTRAN IV, which had served as a de facto standard), and ''Basic FORTRAN'' (based on FORTRAN II, but stripped of its machine-dependent features). The FORTRAN defined by the first standard, officially denoted X3.9-1966, became known as ''FORTRAN 66'' (although many continued to term it FORTRAN IV, the language on which the standard was largely based). FORTRAN 66 effectively became the first industry-standard version of FORTRAN. FORTRAN 66 included: * Main program, , , and program units * , , , , and
data type In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
s * , , and statements * statement for specifying initial values *
Intrinsic In science and engineering, an intrinsic property is a property of a specified subject that exists itself or within the subject. An extrinsic property is not essential or inherent to the subject that is being characterized. For example, mass ...
and (e.g., library) functions * Assignment statement * , computed , assigned , and statements * Logical and arithmetic (three-way) statements * loop statement * , , , , and statements for sequential I/O * statement and assigned format * , , , and statements * Hollerith constants in and statements, and as arguments to procedures * Identifiers of up to six characters in length * Comment lines * line


FORTRAN 77

After the release of the FORTRAN 66 standard, compiler vendors introduced several extensions to ''Standard Fortran'', prompting ANSI committee X3J3 in 1969 to begin work on revising the 1966 standard, under sponsorship of
CBEMA The InterNational Committee for Information Technology Standards (INCITS), (pronounced "insights"), is an ANSI The American National Standards Institute (ANSI ) is a private non-profit organization A nonprofit organization (NPO), also k ...
, the Computer Business Equipment Manufacturers Association (formerly BEMA). Final drafts of this revised standard circulated in 1977, leading to formal approval of the new FORTRAN standard in April 1978. The new standard, called ''FORTRAN 77'' and officially denoted X3.9-1978, added a number of significant features to address many of the shortcomings of FORTRAN 66: * Block and statements, with optional and clauses, to provide improved language support for
structured programming Structured programming is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with impl ...
* loop extensions, including parameter expressions, negative increments, and zero trip counts * , , and statements for improved I/O capability * Direct-access file I/O * statement, to override implicit conventions that undeclared variables are INTEGER if their name begins with I, J, K, L, M, or N (and REAL otherwise) * data type, replacing Hollerith strings with vastly expanded facilities for character input and output and processing of character-based data * statement for specifying constants * statement for persistent local variables * Generic names for intrinsic functions (e.g. also accepts arguments of other types, such as or ). * A set of intrinsics () for lexical comparison of strings, based upon the
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding Character encoding is the process of assigning numbers to graphical Graphics (from Greek Greek may refer to: Greece Anything of, ...
collating sequence. (These ASCII functions were demanded by the
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, in their conditional approval vote.) In this revision of the standard, a number of features were removed or altered in a manner that might invalidate formerly standard-conforming programs. ''(Removal was the only allowable alternative to X3J3 at that time, since the concept of "
deprecation In several fields, especially computing, deprecation is a term for the discouragement of use of some terminology, feature, design, or practice, typically because it has been superseded or is no longer considered efficient or safe, without complete ...
" was not yet available for ANSI standards.)'' While most of the 24 items in the conflict list (see Appendix A2 of X3.9-1978) addressed loopholes or pathological cases permitted by the prior standard but rarely used, a small number of specific capabilities were deliberately removed, such as: * Hollerith constants and
Hollerith Herman Hollerith (February 29, 1860 – November 17, 1929) was an American businessman, inventor, and statistician who developed an electromechanical tabulating machine The tabulating machine was an electromechanical machine designed to assist ...
data, such as GREET = 12HHELLO THERE! * Reading into an H edit (Hollerith field) descriptor in a FORMAT specification * Overindexing of array bounds by subscripts DIMENSION A(10,5) Y= A(11,1) * Transfer of control out of and back into the range of a DO loop (also known as "Extended Range")


Variants: Minnesota FORTRAN

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computers had another version of FORTRAN 77, called Minnesota FORTRAN (MNF), designed especially for student use, with variations in output constructs, special uses of COMMON and DATA statements, optimization code levels for compiling, detailed error listings, extensive warning messages, and debugging features. MNF was developed by people (Liddiard & Mundstock) at the
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University of Minnesota
. MNF was available basically for free.


Transition to ANSI Standard Fortran

The development of a revised standard to succeed FORTRAN 77 would be repeatedly delayed as the standardization process struggled to keep up with rapid changes in computing and programming practice. In the meantime, as the "Standard FORTRAN" for nearly fifteen years, FORTRAN 77 would become the historically most important dialect. An important practical extension to FORTRAN 77 was the release of MIL-STD-1753 in 1978. This specification, developed by the
U.S. Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...
, standardized a number of features implemented by most FORTRAN 77 compilers but not included in the ANSI FORTRAN 77 standard. These features would eventually be incorporated into the Fortran 90 standard. * , , , and statements * statement * variant of the statement *
Bit manipulation Bit manipulation is the act of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in ...
intrinsic functions, based on similar functions included in Industrial Real-Time Fortran (ANSI/ISA S61.1 (1976)) The
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1003.9
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Standard, released in 1991, provided a simple means for FORTRAN 77 programmers to issue POSIX system calls. Over 100 calls were defined in the document allowing access to POSIX-compatible process control, signal handling, file system control, device control, procedure pointing, and stream I/O in a portable manner.


Fortran 90

The much-delayed successor to FORTRAN 77, informally known as ''Fortran 90'' (and prior to that, ''Fortran 8X''), was finally released as ISO/IEC standard 1539:1991 in 1991 and an ANSI Standard in 1992. In addition to changing the official spelling from FORTRAN to Fortran, this major revision added many new features to reflect the significant changes in programming practice that had evolved since the 1978 standard: * Free-form source input, also with lowercase Fortran keywords * Identifiers up to 31 characters in length (In the previous standard, it was only six characters). * Inline comments * Ability to operate on arrays (or array sections) as a whole, thus greatly simplifying math and engineering computations. ** whole, partial and masked array assignment statements and array expressions, such as X(1:N)=R(1:N)*COS(A(1:N)) ** statement for selective array assignment ** array-valued constants and expressions, ** user-defined array-valued functions and array constructors. * procedures *
Modules Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a syst ...
, to group related
procedures Procedure may refer to: * Medical procedure * Instructions or recipes, a set of commands that show how to achieve some result, such as to prepare or make something * Procedure (business), specifying parts of a business process * Standard operatin ...
and data together, and make them available to other program units, including the capability to limit the accessibility to only specific parts of the module. * A vastly improved argument-passing mechanism, allowing
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to be checked at compile time * User-written interfaces for generic procedures *
Operator overloading In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a specific task. Programming involves tasks such as: analysis, gener ...
* Derived (structured) data types * New data type declaration syntax, to specify the data type and other attributes of variables *
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by means of the attribute and the and statements * attribute, pointer assignment, and statement to facilitate the creation and manipulation of dynamic
data structure In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of ...

data structure
s * Structured looping constructs, with an statement for loop termination, and and statements for terminating normal loop iterations in an orderly way * . . . construct for multi-way selection * Portable specification of numerical precision under the user's control * New and enhanced intrinsic procedures.


Obsolescence and deletions

Unlike the prior revision, Fortran 90 removed no features. Any standard-conforming FORTRAN 77 program is also standard-conforming under Fortran 90, and either standard should be usable to define its behavior. A small set of features were identified as "obsolescent" and expected to be removed in a future standard. All of the functionalities of these early version features are performed by new Fortran 95 features. Some are kept to simplify porting of old programs but may eventually be deleted.


"Hello, World!" example

program helloworld print *, "Hello, World!" end program helloworld


Fortran 95

''Fortran 95'', published officially as ISO/IEC 1539-1:1997, was a minor revision, mostly to resolve some outstanding issues from the Fortran 90 standard. Nevertheless, Fortran 95 also added a number of extensions, notably from the High Performance Fortran specification: * and nested constructs to aid vectorization * User-defined and procedures * Default initialization of derived type components, including pointer initialization * Expanded the ability to use initialization expressions for data objects * Initialization of pointers to * Clearly defined that arrays are automatically deallocated when they go out of scope. A number of intrinsic functions were extended (for example a argument was added to the intrinsic). Several features noted in Fortran 90 to be "obsolescent" were removed from Fortran 95: * statements using and index variables * Branching to an statement from outside its block * statement * and assigned statement, and assigned format specifiers * Hollerith edit descriptor. An important supplement to Fortran 95 was the ISO technical report ''TR-15581: Enhanced Data Type Facilities'', informally known as the ''Allocatable TR.'' This specification defined enhanced use of arrays, prior to the availability of fully Fortran 2003-compliant Fortran compilers. Such uses include arrays as derived type components, in procedure dummy argument lists, and as function return values. ( arrays are preferable to -based arrays because arrays are guaranteed by Fortran 95 to be deallocated automatically when they go out of scope, eliminating the possibility of
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age. In addition, elements of allocatable arrays are contiguous, and
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is not an issue for optimization of array references, allowing compilers to generate faster code than in the case of pointers.) Another important supplement to Fortran 95 was the
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technical report ''TR-15580: Floating-point exception handling'', informally known as the ''IEEE TR.'' This specification defined support for IEEE floating-point arithmetic and
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exception handling In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest commo ...
.


Conditional compilation and varying length strings

In addition to the mandatory "Base language" (defined in ISO/IEC 1539-1 : 1997), the Fortran 95 language also includes two optional modules: * Varying length character strings (ISO/IEC 1539-2 : 2000) * Conditional compilation (ISO/IEC 1539-3 : 1998) which, together, compose the multi-part International Standard (ISO/IEC 1539). According to the standards developers, "the optional parts describe self-contained features which have been requested by a substantial body of users and/or implementors, but which are not deemed to be of sufficient generality for them to be required in all standard-conforming Fortran compilers." Nevertheless, if a standard-conforming Fortran does provide such options, then they "must be provided in accordance with the description of those facilities in the appropriate Part of the Standard".


Modern Fortran

The language defined by the twenty-first century standards, in particular because of its incorporation of
Object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mai ...
support and subsequently
Coarray Fortran Coarray Fortran (CAF), formerly known as F--, started as an extension of Fortran Fortran (; formerly FORTRAN) is a general-purpose, compiled language, compiled imperative programming, imperative programming language that is especially suited t ...
, is often referred to as 'Modern Fortran', and the term is increasingly used in the literature.


Fortran 2003

''Fortran 2003,'' officially published as ISO/IEC 1539-1:2004, is a major revision introducing many new features. A comprehensive summary of the new features of Fortran 2003 is available at the Fortran Working Group (ISO/IEC JTC1/SC22/WG5) official Web site. From that article, the major enhancements for this revision include: * Derived type enhancements: parameterized derived types, improved control of accessibility, improved structure constructors, and finalizers *
Object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mai ...
support: type extension and inheritance, polymorphism, dynamic type allocation, and type-bound procedures, providing complete support for
abstract data type In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
s * Data manipulation enhancements: allocatable components (incorporating TR 15581), deferred type parameters, attribute, explicit type specification in array constructors and allocate statements, pointer enhancements, extended initialization expressions, and enhanced intrinsic procedures * Input/output enhancements:
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transfer, stream access, user specified transfer operations for derived types, user specified control of rounding during format conversions, named constants for preconnected units, the statement, regularization of keywords, and access to error messages * Procedure pointers * Support for IEEE floating-point arithmetic and
floating-point In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest com ...
exception handling In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest commo ...
(incorporating TR 15580) * Interoperability with the C programming language * Support for international usage: access to
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4-byte characters and choice of decimal or comma in numeric formatted input/output * Enhanced integration with the host operating system: access to
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arguments,
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s, and processor error messages An important supplement to Fortran 2003 was the ISO technical report ''TR-19767: Enhanced module facilities in Fortran.'' This report provided ''sub-modules,'' which make Fortran modules more similar to
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modules. They are similar to
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private child sub-units. This allows the specification and implementation of a module to be expressed in separate program units, which improves packaging of large libraries, allows preservation of trade secrets while publishing definitive interfaces, and prevents compilation cascades.


Fortran 2008

ISO/IEC 1539-1:2010, informally known as Fortran 2008, was approved in September 2010. As with Fortran 95, this is a minor upgrade, incorporating clarifications and corrections to Fortran 2003, as well as introducing some new capabilities. The new capabilities include: * Sub-modules—additional structuring facilities for modules; supersedes ISO/IEC TR 19767:2005 *
Coarray Fortran Coarray Fortran (CAF), formerly known as F--, started as an extension of Fortran Fortran (; formerly FORTRAN) is a general-purpose, compiled language, compiled imperative programming, imperative programming language that is especially suited t ...
—a parallel execution model * The DO CONCURRENT construct—for loop iterations with no interdependencies * The CONTIGUOUS attribute—to specify storage layout restrictions * The BLOCK construct—can contain declarations of objects with construct scope * Recursive allocatable components—as an alternative to recursive pointers in derived types The Final Draft international Standard (FDIS) is available as document N1830. A supplement to Fortran 2008 is the
International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm Norm, the Norm or NORM may refer to: In academic discipline ...
(ISO) Technical Specification (TS) 29113 on ''Further Interoperability of Fortran with C'', which has been submitted to ISO in May 2012 for approval. The specification adds support for accessing the array descriptor from C and allows ignoring the type and rank of arguments.


Fortran 2018

The latest revision of the language (Fortran 2018) was earlier referred to as Fortran 2015. It is a significant revision and was released on 28 November 2018. Fortran 2018 incorporates two previously published Technical Specifications: * ISO/IEC TS 29113:2012 Further Interoperability with C * ISO/IEC TS 18508:2015 Additional Parallel Features in Fortran Additional changes and new features include support for ISO/IEC/IEEE 60559:2011 (the version of the
IEEE floating-point standard The IEEE Standard for Floating-Point Arithmetic (IEEE 754) is a technical standard A technical standard is an established norm or requirement for a repeatable technical task. It is usually a formal document that establishes uniform engineering ...
before the latest minor revision IEEE ), hexadecimal input/output, IMPLICIT NONE enhancements and other changes.


Language features

A full description of the Fortran language features brought by Fortran 95 is covered in the related article, ''
Fortran 95 language features This is an overview of Fortran 95 language features. Included are the additional features of TR-15581:Enhanced Data Type Facilities, which have been universally implemented. Old features that have been superseded by new ones are not described few of ...
''. The language versions defined by later standards are often referred to collectively as 'Modern Fortran' and are described in the literature.


Science and engineering

Although a 1968 journal article by the authors of
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BASIC
already described FORTRAN as "old-fashioned", programs have been written in Fortran for over six decades and there is a vast body of Fortran software in daily use throughout the scientific and engineering communities.
Jay Pasachoff Jay Myron Pasachoff (born 1943) is an American astronomer. Pasachoff is Field Memorial Professor of Astronomy at Williams College and the author of textbooks and tradebooks in astronomy, physics, mathematics, and other sciences. Biography After ...
wrote in 1984 that "physics and astronomy students simply have to learn FORTRAN. So much exists in FORTRAN that it seems unlikely that scientists will change to Pascal (programming language), Pascal,
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, or whatever." In 1993, Cecil E. Leith called FORTRAN the "mother tongue of scientific computing", adding that its replacement by any other possible language "may remain a forlorn hope". It is the primary language for some of the most intensive Supercomputer, super-computing tasks, such as in astronomy, climate modeling, computational chemistry, computational economics,
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,
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, data analysis, hydrological modeling, numerical linear algebra and numerical libraries (LAPACK, IMSL Numerical Libraries, IMSL and NAG Numerical Library, NAG), optimization, satellite simulation, structural engineering, and numerical weather prediction, weather prediction. Many of the floating-point benchmarks to gauge the performance of new computer processors, such as the floating-point components of the Standard Performance Evaluation Corporation, SPEC benchmarks (e.g.
CFP2006
are written in Fortran. Math algorithms are well documented in Numerical Recipes. Apart from this, more modern codes in computational science generally use large program libraries, such as METIS for graph partitioning, PETSc or Trilinos for linear algebra capabilities, Dune (software), DUNE or FEniCS Project, FEniCS for mesh and finite element support, and other generic libraries. Since the early 2000s, many of the widely used support libraries have also been implemented in C and more recently, in C++. On the other hand, high-level languages such as MATLAB, Python (programming language), Python, and R (programming language), R have become popular in particular areas of computational science. Consequently, a growing fraction of scientific programs is also written in such higher-level scripting languages. For this reason, foreign function interface, facilities for inter-operation with C were added to Fortran 2003 and enhanced by the ISO/IEC technical specification 29113, which was incorporated into Fortran 2018 to allow more flexible interoperation with other programming languages. Software for NASA probes Voyager 1 and Voyager 2 was originally written in FORTRAN 5, and later ported to FORTRAN 77. , some of the software is still written in Fortran and some has been ported to C.


Portability

Portability (computer science), Portability was a problem in the early days because there was no agreed upon standard—not even IBM's reference manual—and computer companies vied to differentiate their offerings from others by providing incompatible features. Standards have improved portability. The 1966 standard provided a reference
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and semantics, but vendors continued to provide incompatible extensions. Although careful programmers were coming to realize that use of incompatible extensions caused expensive portability problems, and were therefore using programs such as ''The PFORT Verifier,'' it was not until after the 1977 standard, when the National Bureau of Standards (now National Institute of Standards and Technology, NIST) published ''FIPS PUB 69'', that processors purchased by the U.S. Government were required to diagnose extensions of the standard. Rather than offer two processors, essentially every compiler eventually had at least an option to diagnose extensions. Incompatible extensions were not the only portability problem. For numerical calculations, it is important to take account of the characteristics of the arithmetic. This was addressed by Fox et al. in the context of the 1966 standard by the ''PORT'' library. The ideas therein became widely used, and were eventually incorporated into the 1990 standard by way of intrinsic inquiry functions. The widespread (now almost universal) adoption of the IEEE 754-2008, IEEE 754 standard for binary floating-point arithmetic has essentially removed this problem. Access to the computing environment (e.g., the program's command line, environment variables, textual explanation of error conditions) remained a problem until it was addressed by the 2003 standard. Large collections of library software that could be described as being loosely related to engineering and scientific calculations, such as graphics libraries, have been written in C, and therefore access to them presented a portability problem. This has been addressed by incorporation of C interoperability into the 2003 standard. It is now possible (and relatively easy) to write an entirely portable program in Fortran, even without recourse to a preprocessor.


Obsolete variants

Until the Fortran 66 standard was developed, each compiler supported its own variant of Fortran. Some were more divergent from the mainstream than others. The first Fortran compiler set a high standard of efficiency for compiled code. This goal made it difficult to create a compiler so it was usually done by the computer manufacturers to support hardware sales. This left an important niche: compilers that were fast and provided good diagnostics for the programmer (often a student). Examples include Watfor, Watfiv, PUFFT, and on a smaller scale, FORGO, Wits Fortran, and Kingston Fortran 2. Fortran 5 was marketed by Data General Corp in the late 1970s and early 1980s, for the Data General Nova, Nova, Data General Eclipse, Eclipse, and Data General Eclipse MV/8000, MV line of computers. It had an optimizing compiler that was quite good for minicomputers of its time. The language most closely resembles FORTRAN 66. FORTRAN V was distributed by
Control Data Corporation Control may refer to: Basic meanings Economics and business * Control (management) Control is a function of management which helps to check errors in order to take corrective actions. This is done to minimize deviation from standards and ensur ...
in 1968 for the CDC 6600 series. The language was based upon FORTRAN IV. Univac also offered a compiler for the 1100 series known as FORTRAN V. A spinoff of Univac Fortran V was Athena FORTRAN. Specific variants produced by the vendors of high-performance scientific computers (''e.g.,'' Burroughs Corporation, Burroughs,
Control Data Corporation Control may refer to: Basic meanings Economics and business * Control (management) Control is a function of management which helps to check errors in order to take corrective actions. This is done to minimize deviation from standards and ensur ...
(CDC), Cray, Honeywell,
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
, Texas Instruments, and UNIVAC) added extensions to Fortran to take advantage of special hardware features such as CPU cache, instruction cache, CPU pipeline (computing), pipelines, and vector arrays. For example, one of IBM's FORTRAN compilers (''H Extended IUP'') had a level of optimization which reordered the machine code instruction (computer science), instructions to keep multiple internal arithmetic units busy simultaneously. Another example is ''CFD'', a special variant of FORTRAN designed specifically for the ILLIAC IV supercomputer, running at NASA's NASA Ames Research Center, Ames Research Center. IBM Research Labs also developed an extended FORTRAN-based language called ''VECTRAN'' for processing vectors and matrices. Object-Oriented Fortran was an object-oriented extension of Fortran, in which data items can be grouped into objects, which can be instantiated and executed in parallel. It was available for Sun, Iris, Intel iPSC, iPSC, and nCUBE, but is no longer supported. Such machine-specific extensions have either disappeared over time or have had elements incorporated into the main standards. The major remaining extension is OpenMP, which is a cross-platform extension for shared memory programming. One new extension, Coarray Fortran, is intended to support parallel programming. ''FOR TRANSIT'' was the name of a reduced version of the IBM 704 FORTRAN language, which was implemented for the IBM 650, using a translator program developed at Carnegie in the late 1950s. The following comment appears in the IBM Reference Manual (''FOR TRANSIT Automatic Coding System'' C28-4038, Copyright 1957, 1959 by IBM):
The FORTRAN system was designed for a more complex machine than the 650, and consequently some of the 32 statements found in the FORTRAN Programmer's Reference Manual are not acceptable to the FOR TRANSIT system. In addition, certain restrictions to the FORTRAN language have been added. However, none of these restrictions make a source program written for FOR TRANSIT incompatible with the FORTRAN system for the 704.
The permissible statements were: * Arithmetic assignment statements, e.g., a = b * * GO TO (n1, n2, ..., nm), i * IF (a) n1, n2, n3 * * * DO n i = m1, m2 * * * * * * Up to ten subroutines could be used in one program. FOR TRANSIT statements were limited to columns 7 through 56, only. Punched cards were used for input and output on the IBM 650. Three passes were required to translate source code to the "IT" language, then to compile the IT statements into SOAP assembly language, and finally to produce the object program, which could then be loaded into the machine to run the program (using punched cards for data input, and outputting results onto punched cards). Two versions existed for the 650s with a 2000 word memory drum: FOR TRANSIT I (S) and FOR TRANSIT II, the latter for machines equipped with indexing registers and automatic floating-point decimal (Bi-quinary coded decimal, bi-quinary) arithmetic. Appendix A of the manual included wiring diagrams for the IBM 533 card reader/punch plugboard, control panel.


Fortran-based languages

Prior to FORTRAN 77, a number of preprocessors were commonly used to provide a friendlier language, with the advantage that the preprocessed code could be compiled on any machine with a standard FORTRAN compiler. These preprocessors would typically support
structured programming Structured programming is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with impl ...
, variable names longer than six characters, additional data types, conditional compilation, and even Macro (computer science), macro capabilities. Popular preprocessors included FLECS, iftran, Mortran, MORTRAN, SFtran, S-Fortran, Ratfor, and Ratfiv. Ratfor and Ratfiv, for example, implemented a C-like language, outputting preprocessed code in standard FORTRAN 66. Despite advances in the Fortran language, preprocessors continue to be used for conditional compilation and macro substitution. One of the earliest versions of FORTRAN, introduced in the '60s, was popularly used in colleges and universities. Developed, supported, and distributed by the University of Waterloo, WATFIV, WATFOR was based largely on FORTRAN IV. A student using WATFOR could submit their batch FORTRAN job and, if there were no syntax errors, the program would move straight to execution. This simplification allowed students to concentrate on their program's syntax and semantics, or execution logic flow, rather than dealing with submission Job Control Language (JCL), the compile/link-edit/execution successive process(es), or other complexities of the mainframe/minicomputer environment. A down side to this simplified environment was that WATFOR was not a good choice for programmers needing the expanded abilities of their host processor(s), e.g., WATFOR typically had very limited access to I/O devices. WATFOR was succeeded by
WATFIV WATFIV, or WATerloo FORTRAN IV, developed at the University of Waterloo The University of Waterloo (commonly referred to as Waterloo, UW, or UWaterloo) is a public university, public research university with a main campus in Waterloo, Ontario, C ...
and its later versions. (line programming) LRLTRAN was developed at the Lawrence Radiation Laboratory to provide support for vector arithmetic and dynamic storage, among other extensions to support systems programming. The distribution included the LTSS operating system. The Fortran-95 Standard includes an optional ''Part 3'' which defines an optional conditional compilation capability. This capability is often referred to as "CoCo". Many Fortran compilers have integrated subsets of the C preprocessor into their systems. SIMSCRIPT is an application specific Fortran preprocessor for modeling and simulating large discrete systems. The F (programming language), F programming language was designed to be a clean subset of Fortran 95 that attempted to remove the redundant, unstructured, and deprecated features of Fortran, such as the statement. F retains the array features added in Fortran 90, and removes control statements that were made obsolete by structured programming constructs added to both FORTRAN 77 and Fortran 90. F is described by its creators as "a compiled, structured, array programming language especially well suited to education and scientific computing". Essential Lahey Fortran 90 (ELF90) was a similar subset. Lahey and Fujitsu teamed up to create Fortran for the Microsoft .NET Framework. Silverfrost FTN95 is also capable of creating .NET code.


Code examples

The following program illustrates dynamic memory allocation and array-based operations, two features introduced with Fortran 90. Particularly noteworthy is the absence of loops and / statements in manipulating the array; mathematical operations are applied to the array as a whole. Also apparent is the use of descriptive variable names and general code formatting that conform with contemporary programming style. This example computes an average over data entered interactively. program average ! Read in some numbers and take the average ! As written, if there are no data points, an average of zero is returned ! While this may not be desired behavior, it keeps this example simple implicit none real, dimension(:), allocatable :: points integer :: number_of_points real :: average_points, positive_average, negative_average average_points = 0.0 positive_average = 0.0 negative_average = 0.0 write (*,*) "Input number of points to average:" read (*,*) number_of_points allocate (points(number_of_points)) write (*,*) "Enter the points to average:" read (*,*) points ! Take the average by summing points and dividing by number_of_points if (number_of_points > 0) average_points = sum(points) / number_of_points ! Now form average over positive and negative points only if (count(points > 0.) > 0) positive_average = sum(points, points > 0.) / count(points > 0.) if (count(points < 0.) > 0) negative_average = sum(points, points < 0.) / count(points < 0.) ! Print result to terminal write (*,'(a,g12.4)') 'Average = ', average_points write (*,'(a,g12.4)') 'Average of positive points = ', positive_average write (*,'(a,g12.4)') 'Average of negative points = ', negative_average end program average


Humor

During the same FORTRAN standards committee meeting at which the name "FORTRAN 77" was chosen, a satirical technical proposal was incorporated into the official distribution bearing the title "Letter O considered harmful, Considered Harmful". This proposal purported to address the confusion that sometimes arises between the letter "O" and the numeral zero, by eliminating the letter from allowable variable names. However, the method proposed was to eliminate the letter from the character set entirely (thereby retaining 48 as the number of lexical characters, which the colon had increased to 49). This was considered beneficial in that it would promote structured programming, by making it impossible to use the notorious statement as before. (Troublesome statements would also be eliminated.) It was noted that this "might invalidate some existing programs" but that most of these "probably were non-conforming, anyway". When X3J3 debated whether the minimum trip count for a DO loop should be zero or one in Fortran 77, Loren Meissner suggested a minimum trip count of two—reasoning ''(tongue-in-cheek)'' that if it was less than two then there would be no reason for a loop! When assumed-length arrays were being added, there was a dispute as to the appropriate character to separate upper and lower bounds. In a comment examining these arguments, Dr. Walt Brainerd penned an article entitled "Astronomy vs. Gastroenterology" because some proponents had suggested using the star or asterisk ("*"), while others favored the colon (":"). Variable names beginning with the letters I–N have a default type of integer, while variables starting with any other letters defaulted to real, although programmers could override the defaults with an explicit declaration. This led to the joke: "In FORTRAN, GOD is REAL (unless declared INTEGER)."


See also

* f2c * FORMAC (programming language), FORMAC * List of compilers#Fortran compilers, List of Fortran compilers * List of numerical libraries#Fortran, List of Fortran numerical libraries * List of programming languages * Matrix representation * Row-major order * Spaghetti code


References


Further reading

;Language standards * Informally known as FORTRAN 66. * Also known as
ISO The International Organization for Standardization (ISO ) is an international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task w ...
1539–1980, informally known as FORTRAN 77. * Informally known as Fortran 90. * Informally known as Fortran 95. There are a further two parts to this standard. Part 1 has been formally adopted by ANSI. * Informally known as Fortran 2003. * Informally known as Fortran 2008. ;Related standards * * ;Other reference material * * * * * ;Books * * * * * * * * * * * * * * * * * * * * * ;Articles * * * * * *


External links


ISO/IEC JTC1/SC22/WG5
the official home of Fortran standards
Fortran Standards Documents
GFortran standards
fortran-lang.org
(2020).
History of FORTRAN and Fortran II
Computer History Museum * Valmer Norrod, et al.
''A self-study course in FORTRAN programing—Volume I—textbook''
Computer Science Corporation El Segundo, California (April 1970). NASA (N70-25287). * Valmer Norrod, Sheldom Blecher, and Martha Horton
''A self-study course in FORTRAN programing—Volume II—workbook''
NASA CR-1478 (April 1970), NASA (N70-25288). {{Authority control Fortran, Fortran programming language family, American inventions Array programming languages Computer standards Numerical programming languages Object-oriented programming languages Procedural programming languages High-level programming languages IBM software Programming languages created in 1957 Programming languages with an ISO standard Statically typed programming languages Unix programming tools