Fortran Subprogramming

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ub programming

Dept. of ChemiCal engineering


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Introduction Complex problems can be easily solved by using

divide-and-conquer strategy.

Problem is divided into a number of simpler sub-problems.

Each of these sub-problems are considered andsolved individually.

The complete solution is then a combination ofsolution to all these subproblems, i.e. subprogramswith the main program.



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Two types of subprogram in FORTRAN:

1. Function subprogram

2. Subroutine subprogram

Subprogram may also be I n te rna l or x te rna l . Usefulprocedures may be collected together as libraries. Suchcollections are called Modu l e s .


ub programming

Main programs (i.e. everything we have seen so far),

external subprograms, and modules are referred to asp rog ram un i ts .


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Internal Subprogram


ub programmingPROGRAM progam_name

IMPLICIT NONE

[declaration statements]

[executable statements]CONTAINS

FUNCTION Name( [argument list] )

[declaration statements][executable statements]

END FUNCTION [Name]

END PROGRAM program_name

General

Syntax of

Internal

function


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Function Subprogram


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Function heading is a FUNCTION statement of the

form:

Name of the functionMay be any legal FORTRAN

identifier

List of identifiers separated bycommas used to pass

information to the function

subprogram

FUNCTION name (formal-argument-list)

Heading Part


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Function Subprogram


ub programmingSpecification Part

Specification part of a function subprogram has thesame form as the specification part of a FORTRANmain program.

It must include a specification of the type of thefunction.


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Function Subprogram


ub programmingExecution part

The execution part of a function subprogram

has the same form as the execution part of aFORTRAN program.

It must include at least one statement that

assigns a value to the identifier that names theexpression.

name = expression


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ub programming

PROGRAM Factorial

IMPLICIT NONE

INTEGER I

DO I = 1, 10PRINT*, I, Fact(I)

END DO

CONTAINS

FUNCTION Fact( N )

INTEGER Fact, N,J, Temp

Temp = 1

DO J = 2, N

Temp = J * Temp

END DO

Fact = Temp

END FUNCTION

END PROGRAM Factorial

Problem:Write a program that will show the 1 to 10 in firstcolumn and their factorials in 2nd column.

RUN
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ub programmingPROGRAM Newt on

! Sol ves f ( x) = 0 by Newt on' s methodI MPLI CI T NONEI NTEGER : : I t s = 0 ! i t er at i on count erI NTEGER : : MaxI t s = 20 ! maxi mum i t erat i onsLOGI CAL : : Conver ged = . f al se. ! conver gence f l agREAL : : Eps = 1e- 6 ! maxi mum err orREAL : : X = 2 ! st art i ng guessDO WHI LE ( . NOT. Converged . AND. I t s < MaxI t s)

X = X- F(X) / DF(X)PRI NT*, X, F(X)I t s = I t s + 1Conver ged = ABS( F( X) )


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ub programmingSummary of Internal function

Internal function are placed between a CONTAINS statement

and END statement of main program.

Internal function looks like the main program except the

header and end statement.

Internal function may not contain other subprogram.

Internal function has access of its host program. So the

variable declared in the host program is GLOBAL.


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ub programmingSubroutine

Subroutine subprograms differ from function subprograms

in the following respects:

Functions are designed to return one value.Subroutines often return more than one value, or

they may return no value at all.

Functions return values via function names;

subroutines return values via arguments.

A function is referenced by using its name in an

expression; subroutine is referenced by a CALL

statement


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ub programmingSubroutine Subprogram

Syntax of subroutine subprograms

Subroutine heading

Specification part

Execution part


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ub programmingSubroutine Subprogram

Subroutine heading is a SUBROUTINE statement of the

form:

SUBROUTINE name (argument list)

A subroutine is referenced by a CALL statement of theform:

CALL name (argument list)


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PROGRAM SWAPPING

IMPLICIT NONE

REAL A, BREAD*, A, B

CALL SWOP( A, B )

PRINT*, A, B

CONTAINS

SUBROUTINE SWOP( X, Y )

REAL Temp, X, YTemp = X

X = Y

Y = Temp

END SUBROUTINE

END PROGRAM SWAPPING

Example: Write a program that will take two numbers from theuser and give the result after exchanging their position.

RUN
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ub programmingCLASS ASSIGNMENT

Write a computer program that reads appropriate

dimensions for different geometrical shapes (triangle,parallelogram, circle, trapezoid) and calculates their

areas.

Use sub programming (function and subroutine) to

solve the problem.

Documents

Fortran Subprogramming