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Getting Started With Essential Lahey Fortran 90 ECST Computer Link College of Engineering, Computer Science, and Technology California State University, Los Angeles Update: 9/12/2012 Author: OSO 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 2 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<b 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 3 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 ex 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 “!” 4 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 5 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. 6 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. I + VsS Z = R+jX (ZZ) - 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 7 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. 8 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 (*,*) ' ' 9 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 10 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. 11 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 12

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