Introduction essential Lahey Fortran 90

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INTRODUCTION

Essential Lahey Fortran 90 is a Programming Language just like C/C++. It is essentially a Compiler that interprets sequences of Fortran language statements and has them executed by the computer. After successful execution, results are output on the screen. Fortran is DOS based and may not come with any text editor for writing the source codes. But this can easily be overcome since all operating systems have some kind of text editor. The procedure for opening a text editor in MS Windows will be explained shortly.

Because of it’s DOS based, Fortran does not easily plot graphs like Matlab. So it is recommended to export output data to other applications (e.g. excel) for graphical manipulation.

GETTING STARTED WITH FORTRAN 90

From Start on MS Windows OS, select Essential Lahey Fortran 90. The window of Figure 1 below appears

Figure 1: Fortran Start-up Window

As the figure shows, Fortran 90 start-up window does nothing but point to the default directory of the system. Fortran 90 does not open any special text editor for you to start inserting your program codes. The Start -up window’s main purpose is to compile your source code once it’s been written. But it provides three useful tips to the novice to get started That is:

- Type elf90 to see all options &switches

- Usage: elf90 filenames [switches]

- To quit, type exit
NOTE: It is recommended that you work on two separate windows:

- An MS-DOS window for editing your source codes (programs)

- The Essential Lahey Fortran 90 Start-up window just for compiling, running, and executing your programs.

OPENING A TEXT EDITOR

- Select Start/Command prompt .

- type edit at the MS-DOS prompt to bring up an MS-DOS window. See procedure on Figure 2.

If done successfully, a DOS - based text editor appears. Insert your program codes and saved the file to the appropriate directory. See saving procedure below.

Figure 2: Opening a text editor in DOS

SAVING A FORTRAN 90 SOURCE CODE FILE

A Fortran 90 file is saved with extension “.f90”. Example: my_first_program.f90

COMPILING A SOURCE CODE

From the Fortran window prompt:

- Locate the source file you want to compile. Use dos commands to do so as follows:

- dir to list the files in the current (default) directory.

- Type the drive name where your source file was saved, e. g. a:\..

- use cd command to move to the directory where you saved the source code. Example: if your source code was saved on a:\ drive under the directory name fortran_directory, type cd fortran_directory. Type dir to list files under fortran_directory and make sure my_first_program.f90 source file is there

- compile the source code. For instance, to compile my_first_program.f90, type:

elf90 my_first_program.f90

RUNNING THE EXECUTABLE FILE

IF my_first_program.f90 compiles correctly, Fortran will create a few other files. Among them, an executable named my_first_program.exe. That is the file you will actually run. To do so, type my_first_program. You may exclude the .exe extension. Follow the procedures as prompted by the program.

DATA TYPES NOTATION

Type	Notation	Example
Integer	INTEGER	INTEGER :: a
Real	REAL	REAL :: a
Character	CHARACTER	CHARACTER :: s
Complex Assignment	COMPLEX	COMPLEX :: b
Complex output	(real_a, imaginary_b)	(a,b)

ARITHMETIC OPERATORS

Operator	Notation	Example
Addition	+	a + b
Subtraction	-	a - b
Multiplication	*	a*b
Division	/	a/b
Exponentiation	**	a**b (a to power of b)

RELATIONAL LOGIC OPERATORS

Operator	Notation	Example
Equal to	= =	a= =b
Not equal to	/=	a/=b
Greater than	>	a>b
Greater than or equal	>=	a>=b
Less than	<	a
Less than or equal	<=	a<=b

COMBINATIONAL LOGIC OPERATORS

Operator Function	Notation	Example
Logical AND	.AND.	a .AND. b
Logical OR	.OR.	a .OR. b
Logical Equivalence	.EQV.	a .EQV. b
Logical Non-equivalence	.NEQV.	a .NEQV. b
Logical NOT	.NOT.	.NOT. a

SOME COMMON FORTRAN IN-BEDDED FUNCTIONS

Function	Notation & Argument	Comment
Square Root	SQRT(x)	Square root of x
Absolute Value	ABS(x)	Absolute value of x
Sine Value	SIN(x)	Sine of x
Cosine Value	COS(x)	Cosine of x
Tangent Value	TAN(x)	Tangent of x
Arc Sine Value	ASIN(x)	Inverse sine of x
Arc Cosine Value	ACOS(x)	Inverse cosine of x
Arc tangent	ATAN(x)	Inverse Tangent of x
Exponential e^x	EXP(x)	e to the x power
Base e logarithm	LOG(x)	Natural log of x
Base 10 logarithm	LOG10(x)	Base 10 log of x
Modulo	MOD(a,b)	Remainder of a/b
Maximum	MAX(a,b)	Returns max of a, b
Minimum	MIN(a,b)	Returns min of a, b

BASIC FORTRAN PROGRAMMING STRUCTURE

The basic Fortran Programming structure will be illustrated with a simple example.

EXAMPLE 1:

Write a program that prompts the user to enter two integers to standard input (keyboard). The program then multiplies the two integers and displays the result to standard output (screen).
Program source code:

PROGRAM mul

IMPLICIT NONE

INTEGER :: i, j, k

WRITE (*,*) 'This program multiplies two integers'

WRITE (*,*) 'Enter the integers: '

READ (*,*) i, j
k = i*j ! Take the product of the two numbers
WRITE (*, *) 'Result =',k ! Output result to screen

STOP

END PROGRAM mul
The source code starts with PROGRAM mul and ends with STOP then END PROGRAM mul. mul is the name of the program. All Fortran programs follow this basic structure. IMPLICIT NONE is used to turn off default typing in Fortran. Must be used to prevent errors in a program where variables types must explicitly be declared.

Note also that comments are preceded by “!”

COMPILING mul.f90 source code

The procedure below compiles mul.f90 source code:

Z:\FORTRAN>elf90 mul.f90
The line above indicates that mul.f90 was saved in z:\ drive under a directory created by the user, and named FORTRAN.

elf90 mul.f90 is the command that compiles the source code.

Note that Z:\FORTRAN directory was set in the Fortran window before compiling the program. See section “Compiling a Source Code” for details.

RUNNING A PROGRAM

The procedure below runs mul.f90 source code if it was compiled successfully:

Z:\FORTRAN> mul
PROGRAM OUTPUT
This program multiplies two integers

Enter the integers: -57 13
Result = -741
Program completed

Press Enter to Continue.

MORE PROGRAMMING EXAMPLES

EXAMPLE 2: SQRT COMPUTATION

Compute the square root of the product of two real numbers. If one of the input numbers is negative, the program must announce that the result will be a complex number.
The program uses IF statement as well as logical .AND., .OR. statements. If one of the input numbers is negative, the program announces that the result will be a complex number.

NOTE: Fortran does not compute the square root of a negative number to obtain a complex number. For this reason, the program switches to a slightly different computation method (i.e. multiplying the arguments of SQRT by -1)

See program code on next page
PROGRAM ff
! Purpose: Compute the square root of the product of two real numbers
IMPLICIT NONE

REAL :: x, y

REAL :: z ! Square Root of product(x,y)
WRITE (*,*) 'Please enter the two real values: '

READ (*,*) x, y
IF (((x < 0) .AND. (y>0)).OR. ((y<0) .AND. (x>0))) THEN

WRITE (*,*) 'The product is negative ==> Complex Answer'

z = SQRT(-x*y)

WRITE (*,*) 'Result =',z,'j'

END IF

! Multiply the two integers and

z = SQRT(x*y) ! take the square root of the product
WRITE (*, *) 'Result =',z ! Output result to screenWS

STOP

END PROGRAM ff

EXAMPLES OF SQRT RESULTS OUTPUT

a)

Please enter the two real values: 12.33 -4.7
The product is negative ==> Complex Answer

Result = 7.61256 j
SQRT argument negative (see "SQRT Function" in the Essential Lahey Fortran 90

Reference).

Error occurred at line 18 of file ff.f90.

Program completed
Note the error message in the result although the argument of SQRT() was made positive.
b)

Please enter the two real values: -8.67 -13
Result = 10.6165
Program completed

Press Enter to Continue.
c)

Please enter the two real values: 98 33.49
Result = 57.2889
Program completed

Press Enter to Continue.

EXAMPLE 3: SINGLE PHASE POWER COMPUTATION

Compute the current, real, reactive, apparent power, and the power factor supplied to the load of the single phase circuit below.

Vs_SZ = R+jX (Z_Z)

Source Code:

PROGRAM power
! Purpose: Compute the current, real, reactive, apparent power, and

! the power factor of supplied to a load.
IMPLICIT NONE
! Declare input parameters
REAL :: Vsource, Theta_source, Theta_sc ! Voltage and angle of source

COMPLEX :: Z_load ! To be input in the form (R,X) --> R+jX
! Declare Output values
REAL :: I_current, Z, PF, Preal, Preactive, Papparent

REAL :: Theta, Theta_z, Theta_i
! Initialize input parameters
WRITE (*,*) 'Please input the source voltage '

WRITE (*,*) 'and angle (in degrees) respectively.'

WRITE (*,*) '(Example: 250 0) '

READ (*,*) Vsource, Theta_source
WRITE (*, *) 'Input complex components of load Z of the form'

WRITE (*,*) 'Z = R+jX (input example: 1200, 75) '

READ (*,*) Z_load
! Compute output results
Theta_sc = Theta_source*3.141593/180 !Degrees to radians

Theta_z = ATAN(AIMAG(Z_load)/REAL(Z_load)) ! Angle due to load

Theta_i = Theta_sc - Theta_z ! Current angle

Theta = Theta_sc - Theta_i ! p.f. angle

PF = COS(Theta) ! Power Factor

Z = ABS(Z_load) ! Load Magnitude

I_current = Vsource/Z ! Current Magnitude

Preal = Vsource*I_current*PF ! Real Power

Preactive = Vsource*I_current*SIN(Theta) ! Reactive Power

Papparent = Vsource*I_current ! Apparent Power
! Output computed results
WRITE (*,*) 'Load Current: ', I_current,'Amps'

WRITE (*,*) 'Real Power: ', Preal,'Watts'

WRITE (*,*) 'Reactive Power: ', Preactive,'Vars'

WRITE (*,*) 'Apparent Power: ', Papparent,'VA'

WRITE (*,*) 'Power factor: ', PF

WRITE (*,*) 'At an angle of: ', Theta*180/3.141593,'degrees'
STOP

END PROGRAM power
REMARK: Note the computation of Theta_z in the program. AIMAG(Z_load) is the imaginary part of Z_load REAL(Z_load), the real part.

POWER COMPUTATION OUTPUT EXAMPLE

Z:\FORTRAN>power
Please input the source voltage

and angle (in degrees) respectively.

(Example: 250 0) 450 30
Input complex components of load Z of the form

Z = R+jX (input example: 1200, 75) 2100, 173
Load Current: 0.213562 Amps

Real Power: 95.7786 Watts

Reactive Power: 7.89033 Vars

Apparent Power: 96.1030 VA

Power factor: 0.996624

At an angle of: 4.70945 degrees
Program completed

Press Enter to Continue.

EXAMPLE 4: DELTA-TO-Y Y-TO-DELTA IMPEDANCES CONVERSION

Zab

a b a b

Za Zb
Zca Zbc

Zc

c
c

 - Y Y - 

Source code:
PROGRAM convert
IMPLICIT NONE
REAL :: Zab, Zbc, Zca ! Impedances in a Delta Connection

REAL :: Za, Zb, Zc ! Inpedance in a Y Connection

CHARACTER (len=1) :: num ! Selection identifier
WRITE (*,*) 'Convert Three-phase impedances:'

WRITE (*,*) 'Delta to Y equivalent impedances and vice versa.'

WRITE (*,*) ' '

DO

WRITE (*,*) 'Press 1 to convert from Delta to Y'

WRITE (*,*) 'Press 2 to convert from Y to Delta: '

WRITE (*,*) 'Press ANY OTHER KEY to quit.'

WRITE (*,*) 'Choice: '

READ (*,*) num
SELECT CASE (num)
CASE ('1')

WRITE (*,*) 'Enter the values of Zab, Zbc, Zca: '

READ (*,*) Zab, Zbc, Zca
Za = (Zab*Zca)/(Zab+Zbc+Zca)

Zb = (Zbc*Zab)/(Zab+Zbc+Zca)

Zc= (Zbc*Zca)/(Zab+Zbc+Zca)
WRITE (*,*) 'Y-connection equivalent impedances:'

WRITE (*,*) 'Za =',Za

WRITE (*,*) 'Zb =',Zb

WRITE (*,*) 'Zc =',Zc

WRITE (*,*) ' '

CASE ('2')
WRITE (*,*) 'Enter the values of Za, Zb, Zc: '

READ (*,*) Za, Zb, Zc
Zab = (Za*Zb + Zb*Zc + Zc*Za)/Zc

Zbc = (Za*Zb + Zb*Zc + Zc*Za)/Za

Zbc = (Za*Zb + Zb*Zc + Zc*Za)/Za

Zca = (Za*Zb + Zb*Zc + Zc*Za)/Zb

WRITE (*,*) 'Delta-connection equivalent impedances:'

WRITE (*,*) 'Zab =',Zab

WRITE (*,*) 'Zbc =',Zbc

WRITE (*,*) 'Zca =',Zca

WRITE (*,*) ' '
CASE DEFAULT

WRITE (*,*) 'You have chosen to quit. Good bye...'

EXIT

END SELECT

END DO

STOP

END PROGRAM convert

A CONVERSION COMPUTATION EXAMPLE

Z:\FORTRAN>convert
Convert Three-phase impedances:

Delta to Y equivalent impedances and vice versa.
Press 1 to convert from Delta to Y

Press 2 to convert from Y to Delta:

Press ANY OTHER KEY to quit.

Choice: 1
Enter the values of Zab, Zbc, Zca: 200 350 80
Y-connection equivalent impedances:

Za = 25.3968 ohms

Zb = 111.111 ohms

Zc = 44.4444 ohms
Press 1 to convert from Delta to Y

Press 2 to convert from Y to Delta:

Press ANY OTHER KEY to quit.

Choice: 2
Enter the values of Za, Zb, Zc: 250 250 250
Delta-connection equivalent impedances:

Zab = 750.000 ohms

Zbc = 750.000 ohms

Zca = 750.000 ohms

Press 1 to convert from Delta to Y

Press 2 to convert from Y to Delta:

Press ANY OTHER KEY to quit.

Choice: k
You have chosen to quit. Good bye...
Program completed

Press Enter to Continue.

TABLE OF CONTENTS

INTRODUCTION 1

GETTING STARTED WITH FORTRAN 90 1

OPENING A TEXT EDITOR 2

SAVING A FORTRAN 90 SOURCE CODE FILE 2

COMPILING A SOURCE CODE 2

RUNNING THE EXECUTABLE FILE 3

DATA TYPES NOTATION 3

ARITHMETIC OPERATORS 3

RELATIONAL LOGIC OPERATORS 3

COMBINATIONAL LOGIC OPERATORS 3

SOME COMMON FORTRAN IN-BEDDED FUNCTIONS 4

BASIC FORTRAN PROGRAMMING STRUCTURE 4

EXAMPLE 1: 4

COMPILING mul.f90 source code 5

RUNNING A PROGRAM 5

EXAMPLE 2: SQRT COMPUTATION 5

EXAMPLES OF SQRT RESULTS OUTPUT 6

EXAMPLE 3: SINGLE PHASE POWER COMPUTATION 7

POWER COMPUTATION OUTPUT EXAMPLE 8

EXAMPLE 4: DELTA-TO-Y Y-TO-DELTA IMPEDANCES CONVERSION 9

A CONVERSION COMPUTATION EXAMPLE 10

TABLE OF FIGURES

Figure 1: Fortran Start-up Window 1

Figure 2: Opening a text editor in DOS 2