Fortran Tutorial
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Fortran Tutorial. Fortran 77. program progname ! ! Comments are preceded by ! “!” or “C” ! implicit none C C Data initialization to C follow… C integer :: i,j,k,n,m real :: x,y,z ! integer, dimension(3) :: larray

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Fortran Tutorial

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Fortran tutorial

Fortran Tutorial

Fortran 77

program progname

!

! Comments are preceded by

! “!” or “C”

!

implicit none

C

C Data initialization to

C follow…

C

integer :: i,j,k,n,m

real :: x,y,z

!

integer, dimension(3) :: larray

real, dimension(3) :: rvec,forces

!

real, dimension(0:3,8) :: tensor

!

character(len=6) :: name ! Comment.

!

logical :: some_flag,another_flag

!

complex :: phase,factor

!

real, parameter :: four = 4.0E0

!

! =====================================

! Beyond this point expressions are

! allowed.

7-72 spaces for code

qqqqqqCODE

Must leave six spaces for “statement label”.

Single precision (kind=4)

Double precision (kind=8)

Comments can be added at the end of a line.


Fortran tutorial

Fortran Tutorial

!

! Data initiation continued...

!

x = 1.50E0

y = 10.0E0

!

rvec(1) = 0.100E0

rvec(2) = 0.000E0

rvec(3) = 0.750E0

!

forces(1:3) = 0.00E0

!

phase = (2.0E0,1.25E0)

!

tensor(0,:) = 0.0E0

tensor(1:3,:) = 3.0E0

!

name = ‘PRESS’

some_flag = .true.

another_flag = .false.

!

do i=1,3

forces(i) = 0.0E0

enddo

do i=1,3

do j=1,3

tensor(i,j) = 3.0E0

enddo

enddo


Fortran tutorial

Fortran Tutorial

!

! Conditional statements

!

if (i == 3) statement

if (i > 4 ) statement

if (i <= 2 ) statement

!

if (x >= 0.0E0 ) then

statement

statement

statement

endif

!

if ( a > x .and. b < y ) then

if ( c == 0.0E0 ) then

statement

statement

else if ( c > 0.0E0 ) then

statement

statement

else

statement

statement

endif

endif

!

if (some_flag) then ...

if (.not.another_flag) then ...

!

if (name == ‘PRESS’ ) then ...

!

F90 F77 Operation

== .eq. Equal to

/= .ne. Not equal to

> .gt. Greater than

>= .ge. Greater or equal to

< .lt. Less than

<= .le. Less than or equal to


Fortran tutorial

Fortran Tutorial

!

! Loop statements

!

do i=1,3

statement

statement

enddo

!

do i=1,n-1

do j=i+1,n

statement

statement

statement

enddo

enddo

!

do i=1,10

statement

if (force(i) > 10.0E0) exit

statement

enddo

!

do

statement

statement

if (condition) break

enddo

!

do i=1,10

statement

if (condition) goto 10

statement

enddo

10 continue


Fortran tutorial

Fortran Tutorial

!

! Loop statements (continued)

!

do i=1,n,3 ! Increment by 3

statement

statement

enddo

!

! While loop...

!

i = 0

do while (i<n)

statement

statement

i = i + 1

enddo

!


Fortran tutorial

Fortran Tutorial

!

! Expressions

!

x = a * b / c

!

x = a**3 * b + c/d

!

x = exp( sqrt( x**2 + y**2 + &

z**2) )

!

! Complex variables...

!

phase = (1.0E0,1.0E0) ! Equals 1+i

!

phase = cmplx(a,b) ! Equals a+ib

!

c = conjg(phase) ! Equals a-ib

!

a = real(phase)

b = aimag(phase)

!

! Floating points & integers...

!

i = 3.45E0 ! Equals 3

i = -2.76E0 ! Equals –3

!

! Good practice ...

!

i = int( real(j)*force(k)/2.0E0 )

!

Fortran 77

x = exp( sqrt( x**2 + y**2 +

& z**2) )

Continuation symbol at space #5


Fortran tutorial

Fortran Tutorial

!

! Subroutines...

!

call myroutine(a,b,3,x,y,z,flag)

!

stop

end

! -----------------------------------

subroutine myroutine(a,b,k,x,y,z,root)

!

implicit none

real :: a,b,x,y,z

integer :: k

logical :: root

!

integer :: i

!

a = (x**2+y**2+z**2)

do i=1,k

a = a + b**I

enddo

!

if (root) a = sqrt(a)

!

return

end subroutine

!--------------------------------------

End of program

Begin the subroutine

Return control back to calling program or routine

End the routine


Fortran tutorial

Fortran Tutorial

!

! User functions...

!

integer :: n,x,factorial

.

.

x = factorial(n)

.

stop

end

! -----------------------------------

function factorial(n)

!

implicit none

integer :: factorial,n

!

integer :: i

!

if (i<0) return(0)

if (i=0) return(1)

!

factorial = 1

do i=1,n

factorial = factorial * i

enddo

!

return

end function

!--------------------------------------


Fortran tutorial

Fortran Tutorial

ininteger n spaces long.

fn.dfloating point n spaces long, d spaces

after the decimal place.

ancharacter string n spaces long.

en.d exponential n spaces long, d spaces

after the decimal point. (n>=d+7)

esn.dscientific n spaces long, d spaces

after the decimal point. (n>=d+7)

lnlogical n spaces long.

xspace.

ttab.

!

! Output...

!

! Free format ->

!

write(*,*) ‘This is a tutorial.’

write(*,*) ‘The answer is ‘,i

!

! Fixed format ->

!

write(*,100) i

100 format(‘This is a tutorial.’,/, &

‘The answer is ‘,i3)

!

write(*,200) (force(i),I=1,3)

200 format(/,’Particle force = ‘,3f4.1)

!

name = ‘alpha’

do i=1,n

write(*,300) name,i,x,y,z

enddo

300 format(‘ data set ‘,a5,’: iter = ‘, &

i3,’, force = ‘,3(x,f4.1))

!

Particle force = 1.0 0.4 1.8

data set alpha: iter = 1, force = 10.1 1.2 –2.9

data set alpha: iter = 2, force = 1.4 0.1 –4.3

data set alpha: iter = 3, force = 2.3 0.3 2.5

data set alpha: iter = 4, force = -2.1 1.2 2.8

data set alpha: iter = 5, force = -3.9 **** –0.2


Fortran tutorial

Fortran Tutorial

!

! External files...

!

open(unit=6,file=‘myfile’, &

form=‘formatted’,status=‘old’)

!

! File with I/O unit=6 is now open.

!

! Unformatted read--->

!

read(6,*) a,b,c ! These are

read(6,*) x,y,z ! on separate

read(6,*) (force(i),i=1,3) ! lines.

!

! Formatted read--->

!

read(6,100) i,j,name

100 format(2x,i3,x,i3,3x,a6)

!

close(unit=6) ! Close file.

!

! --------------------------------------

! Write to files...

!

open(unit=7,file=‘output’, &

form=‘formatted’,status=‘new’)

!

write(7,200) name,x,y,z

200 format(2x,a6,’ data -> ‘,3(2x,f5.2))

!

close(unit=7)

!

Status clause (possible values)

‘old’,’new’,’unknown’,

‘scratch’,’replace’

form clause (possible values)

‘formatted’,

‘unformatted’


Fortran tutorial

Fortran Tutorial

COMPILING...

-> f90 –o executable program.f

Linking many files

-> f90 –c code1.f

-> f90 –c code2.f

-> f90 –o executable code1.o code2.o program.f

Example:

-> f90 –c code1.f

-> f90 –c code2.f

-> f90 –o prog.x code1.o code2.o program.f

-> prog.x

To run in “background”

-> prog.x &

->

Check the status of a run

-> ps –a

Kill a run

-> kill –9 6445

Run the program

Code will run in background and allow you use other commands.

Include process ID (from”ps –a”)


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