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Fortran

Fortran. General: Mathematical computations (engineering, computational biology) FORmula TRANslation  FORTRAN Started in 1950's at IBM Fortran 66 Fortran 77  this class Fortran 90 (95) Why: dominant programming language used in engineering applications

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Fortran

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  1. Fortran • General: • Mathematical computations (engineering, computational biology) • FORmula TRANslation  FORTRAN • Started in 1950's at IBM • Fortran 66 • Fortran 77  this class • Fortran 90 (95) • Why: • dominant programming language used in engineering applications • ( > 50 % engineering applications)

  2. Layout 1234567890123456789012345678901234567890123456789012 ... 34567890 Column 1 marked C for comment line 73-80 Sequence number 1-5 statement number 6 continuation 7-72 main text

  3. Fortran 77 is not a free-format language, • strict set of rules for source code • column position rules: • Col. 1 : Blank, or a "c" or "*" for comments • Col. 2-5 : Statement label (optional) • Col. 6 : Continuation of previous line (optional) • Col. 7-72 : Statements • Col. 73-80: Sequence number (optional, rarely used today)

  4. No difference between upper or lower cases No reserved keyword Integer Real Complex (1.0,2.2), (1.0e0,0.22e1) Logical .true. , .false. Character ‘a’, ‘123’ Double precision: 3.14159265d0 Variable names

  5. Variable names generally consist of 1-6 characters • chosen from the letters a-z and the digits 0-9 • The first character must be a letter • Case insensitive (upper case, lower case)

  6. integer sum, id, SSN integer*2 short real temp, height double precision temp, height, long complex curr,volt logical done, error character*20 name, names(20) Extra caution: I-N rule

  7. Any names start with I,J,K,L,M,N (i,j,k,l,m,n) To overrule IMPLICIT NONE To add additional implicit variable type IMPLICIT COMPLEX C,X Default integer variable names

  8. A general Fortran program: • a main program (or driver) and • several subprograms (or procedures or subroutines). • program name • declarations • statements • stop • end • subprograms …..

  9. --------------------------------------------------------- program circle real r, area c This program reads a real number r and prints c the area of a circle with radius r. write (*,*) 'Give radius r:' read (*,*) r area = 3.14159*r*r write (*,*) 'Area = ', area stop end

  10. Constant: • parameter (name = constant, ... , name = constant) • parameter (pi=3.14159,c=3.e8) • The "variable" defined in the parameter statement is not a variable but rather a constant whose value can never change • A "variable" can appear in at most one parameter statement • The parameter statement(s) must come before the first executable statement

  11. DATA x,y,z/1.0,2.2,3.e0/ placed before executable statements data

  12. Arithmetic Expressions operand operator operand ** {exponentiation} *,/ {multiplication, division} +,- {addition, subtraction} caution for division integer/integer  perform integer division 5/3  1 5.0/3.0  1.66667 5.0/3  1.66667

  13. Logical expressions Logical expressions can only have the value .TRUE. or .FALSE.. A logical expression can be formed by comparing arithmetic expressions using the following relational operators: meaning .LT. < .LE. <= .GT. > .GE. >= .EQ. = .NE. !=

  14. Assignment The assignment has the form variable_name = expression Evaluate the right hand side and assign the resulting value to the variable on the left. For example, area = pi * r**2

  15. Type conversion different data types occur in the same expression  type conversion implicitly: real x x = x + 1 explicitly: int (variable) int(2.3)  2 real … real(2) 2.0 dble … ichar … char …

  16. key-board input / screen output read (*,*) list-of-variables write(*,*) list-of-variables integer m, n real x, y read(*,*) m, n ! -1 100 read(*,*) x, y ! -1.0 1e+2 write(*,*) m,n write(*,*) x,y

  17. Format statement write(*, label) list-of-variables label format format-code Eg. format(1x,i3,1x,f5.2) A - text string D - double precision numbers E - real numbers, exponent notation F - real numbers, fixed point format I - integer X - horizontal skip (space) / - vertical skip (newline)

  18. x = 0.025 write(*,100) 'x=', x 100 format (A,F) write(*,110) 'x=', x 110 format (A,F5.3) write(*,120) 'x=', x 120 format (A,E) write(*,130) 'x=', x 130 format (A,E8.1) write (*,999) x 999 format ('The answer is x = ', F8.3) Output: x= 0.0250000 x=0.025 x= 0.2500000E-01 x= 0.3E-01 The answer is x= 0.250

  19. FILE I/O • open statement (no need to specific read/write at open) • open(unit=15,file=‘input1.dat’,status=‘old’) • open(unit=16,file=‘output.dat’,status=‘new’) • open(11,file=‘newinput.dat’) • open(12,file=‘newoutput.dat’)

  20. Write statement: • write(unit number,label) variable list • open(11,file=‘output.dat’,status=‘new’) • write(11,130) 'x=', x • 130 format (A,E8.1) • output.dat • x= 0.3E-01

  21. Read statement: • read (unit number, label) variable list • open(10,file=‘input.dat’,status=‘old’) • read(10,*) x,y • input.dat • 10.0 20.0

  22. Source code format • Data type • Simple I/O • Control statement • if • block if • if-else • if-else if • do • go to

  23. logical expression executable statement • if (logical expression) executable statement • logical expression = .true. executes statement • logical expression = .false. do not execute statement false true

  24. if (x .LT. 0) x = -x ! Find the absolute value of x if (weight.gt.20) count=count+1 program checknumber write(*,*) ‘input number’ read(*,*) n If (n.lt.0) write(*,*) ‘negative number’ If(n.eq.0) write(*,*) ‘value equal to 0’ If(n.gt.0) write(*,*) ‘positive output’ stop end

  25. if (logical expression) then statements endif if ( grade.gt.1.67) then sumh=sumh+hour sumg=sumg+grade course=course+1 endif gpa=sumg/sumh statements

  26. If (logical expression ) then statement 1 statement 2 … statement m … else statement a statement b statement c … endif statement group a statement group b

  27. logical expression false true statement group B statement group A

  28. numpos=0 numneg=0 assign x value … If (x.gt.0) then y=sqrt(x)*sin(x) sum=sum+x numpos=numpos+1 else y=log(abs(x)) sum=sum+abs(x) numneg=numneg+1 endif

  29. if (logical expression) then statements else if (logical expression) then statements else if (logical expression) then statements : : else statements endif block 1 block 2 block 3

  30. T block 1 condition 1 T block 2 condition 2 T condition 3 block 3 T block n condition n else block F

  31. Multiprocessor parallel program computer node selection C multiway selection if(myrank.eq.0) then write(*,*) ‘start job on node 0’ … else if(myrank.eq.1) then write(*,*) ‘start job on node 1’ … else if(myrank.eq.2) then write(*,*) ‘start job on node 2’ … else if(myrank.eq.n-2) then write(*,*) ‘start job on node n-2’ else write(*,*) ‘start job on node n-1’ endif

  32. Nested if if (x .GT. 0) then if (x .GE. y) then write(*,*) 'x is positive and x >= y' else write(*,*) 'x is positive but x < y' endif elseif (x .LT. 0) then write(*,*) 'x is negative' else write(*,*) 'x is zero' endif

  33. do label var = expr1, expr2, expr3 statements label continue var: integer exp1: initial value of var exp2: terminating bound exp3: increment step do var = expr1, expr2, expr3 statements enddo popular exp3: default is 1

  34. integer i, n, sum sum = 0 do 10 i = 1, n !do i=1,n sum = sum + i write(*,*) 'i =', i write(*,*) 'sum =', sum 10 continue !enddo integer i do 20 i = 10, 1, -2 write(*,*) 'i =', i 20 continue

  35. Nested loop do index1=1,nmax do index2=1,mmax statements enddo !enddo for index2 enddo !enddo for index1 Typically used in the multiple dimension array manipulation

  36. while (logical expr) do statements enddo i = 1 sum=0 while (i.lt.100) do sum = sum + i i = i+2 enddo

  37. go to n unconditional branch Better to use in do/while loop … do i=1,200 sum=sum+i if(sum.gt.100) goto 20 enddo 20 write(*,*) sum …

  38. n CONTINUE Used to serve as the end of a DO loop n is the statement Example do 9 I=1,100,2 do 8 j=1,4 … 8 continue ... 9 continue CONTINUE

  39. Control statement • if • block if • if-else • if-else if • do • go to • Arrays • Subprograms • Function • Subroutine

  40. One dimensional Array real a1,a2,a3,…a20 real a(20) default, index starts from 1 to 20 a(1) a(2) a(17) a(18) a(19) a(20)

  41. real var(lowerbound:upperbound) • lowerbound < upperbound • bounds must be integer numbers real b(0:19), weird(-162:237) Number of element 20 400 real a(-5:10) a(-5),a(-4),…a(0),a(1),…a(10) a(-5) a(-4) a(7) a(8) a(9) a(10)

  42. 100 real temp(-100:100) open(1,file=‘temp.dat’,status=‘old’) do i=-100,100 read(1,*) temp(i) enddo stop end temp.dat 20 22 . . . 29 Read (1,*)(temp(j), j=-100,100) -100 Temp.dat 20 22 … 29

  43. Two dimensional array --> no pointer real image(200,300),coord(-200:20,-40:200) Fortran stores array by column! data statement data list of variable names /list of values/ data a,b,c/2.3,2.1,1.5/ real a(2,3) data a/1.0,2.0,3.0,4.0,5.0,6.0/ 1 3 5 2 4 6

  44. 3.4 23.1 4.0 11.2 3.4 2.1 10.9 3.1 1.7 1.5 12.1 8.8 7.1 43.2 12.1 23.0 12.1 21.6 32.7 75.2 43.2 3.2 5.5 6.70 real y(4,6) read(*,*) y write(*,*) y stop end Input line: 3.4 10.9 7.1 32.7 23.1 … 2.1 8.8 21.6 6.7 Output : 3.4 10.9 7.1 32.7 23.1 3.1 43.2 75.2 4.0 1.7 12.1 43.2 11.2 1.5 23.0 3.2 3.4 12.1 12.1 5.5 2.1 8.8 21.6 6.7

  45. real y(4,6) do i=1,4 read(*,*) ( y(i,j) , j=1,6) enddo do i=1,4 write(*,*) (y(i,j),j=1,6) enddo stop end inputline: 3.4 23.1 4.0 11.2 3.4 2.1 10.9 3.1 1.7 1.5 12.1 8.8 7.1 43.2 12.1 23.0 12.1 21.6 32.7 75.2 43.2 3.2 5.5 6.70 Output: same as inputline

  46. real y(4,6) read(*,*) (( y(i,j) , j=1,6),i=1,4) write(*,2) (( y(i,j) , j=1,6),i=1,4) format(1x,6f7.1) stop end 2 Intputline: 3.4 23.1 4.0 11.2 3.4 2.1 10.9 3.1 1.7 1.5 12.1 8.8 7.1 43.2 12.1 23.0 12.1 21.6 32.7 75.2 43.2 3.2 5.5 6.70 3.4 23.1 4.0 11.2 3.4 2.1 10.9 3.1 1.7 1.5 12.1 8.8 7.1 43.2 12.1 23.0 12.1 21.6 32.7 75.2 43.2 3.2 5.5 6.70 Outputline:

  47. three dimensional array and multiple dimensional array real a(10,20,30), ab(10,20,30,40) A(j,k,m) j varies most rapidly, k next, m most slowly A(1,1,1), A(2,1,1),…,A(10,1,1) A(1,2,1), A(2,2,1),... real temp(10,10,10) temp(5,5,5)= 21.4 temp(1,2,3)= 20.0 1 2 3 4 5 6 7 8 9 10

  48. Subprogram: • Function • One return value • Subroutine • May have multiple return values

  49. type function name (list-of-variables) declarations statements name=… return end • Functions have a type. This type must also be declared in the calling program. • The return value should be stored in a variable with the same name as the function. • Functions are terminated by the return statement instead of stop • type – integer, complex, real, …

  50. C This is the function function sum(w) real w(3,4) sum=0 do j=1,3 do i=1,4 sum=sum+w(i,j) enddo enddo return end C This is the main program dimension w(3,4) read(*,*) w write(*,*) ‘sum is ‘, sum(w) stop end Inputline: 3.2 1.2 5.4 3.2 9.0 6.5 2.1 12.2 32.1 45.3 1.2 1.2 Output: sum is 122.50

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