1. Fortran Tutorial Fortran 77 7-72 spaces for code qqqqqqCODE
program progname !
! Comments are preceded by
! “!” or “C”
implicit none C
C Data initialization to
C follow…
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.

2. 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

3. Fortran Tutorial ! ! Conditional statements if (i == 3) statement
if (x >= 0.0E0 ) then
statement
endif
if ( a > x .and. b < y ) then
if ( c == 0.0E0 ) then
else if ( c > 0.0E0 ) then
else
if (some_flag) then ...
if (.not.another_flag) then ...
if (name == ‘PRESS’ ) then ...
F F 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

4. Fortran Tutorial ! ! Loop statements do i=1,3 statement enddo
do i=1,n-1
do j=i+1,n
do i=1,10
if (force(i) > 10.0E0) exit do
if (condition) break
do i=1,10
statement
if (condition) goto 10
enddo
10 continue

5. Fortran Tutorial ! ! Loop statements (continued)
do i=1,n, ! Increment by 3
statement
enddo
! While loop...
i = 0
do while (i<n)
i = i + 1

6. Fortran Tutorial Fortran 77 Continuation symbol at space #5 !
! 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 = 3.45E ! Equals 3
i = -2.76E ! 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

7. Fortran Tutorial End of program Begin the subroutine!
! 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

8. 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 !

9. Fortran Tutorial in integer n spaces long. !
fn.d floating point n spaces long, d spaces
after the decimal place.
an character string n spaces long.
en.d exponential n spaces long, d spaces
after the decimal point. (n>=d+7)
esn.d scientific n spaces long, d spaces
ln logical n spaces long.
x space.
t tab. !
! 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 =
data set alpha: iter = 1, force = –2.9
data set alpha: iter = 2, force = –4.3
data set alpha: iter = 3, force =
data set alpha: iter = 4, force =
data set alpha: iter = 5, force = **** –0.2

10. Fortran Tutorial Status clause (possible values)!
! 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’

11. Fortran Tutorial Run the program
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 –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”)