Fortran

Fortran95 is the language of choice to program in MOHID. Although a primitive form of language it proves to be the most efficient and performant in the area of scientific computing. Still widely used in numerical computation. Here's a crash course. Here's a free manual.

Examples

Hello World program

program helloworld

implicit none

write (*,*) "Hello world!"

end program helloworld

Hello world in a module

module modulehelloworld

implicit none

private

public :: showhelloworld

contains

subroutine showhelloworld()
        
        write(*,*) "Hello world!"

end subroutine showhelloworld

end module modulehelloworld

program helloworld

use modulehelloworld, only: showhelloworld

implicit none

call showhelloworld

end program helloworld

Subroutines & functions

Subroutine

program subfunc

implicit none

real :: a,b,c,root1,root2
logical :: realroots
write (*,*) "Hello world!"

write (*,10)
read (*,*) a,b,c

call solvit(a,b,c,root1,root2,realroots)
write (*,20) root1,root2

if (realroots) then
        write(*,*) 'Sorry, there are no real roots'
end if        

10 format('Enter 3 coefficients')
20 format('The roots are ', 2f12.6)
end program subfunc

subroutine solvit(a,b,c,root1,root2,realroots)

!Arguments
real ::a,b,c,root1,root2
logical :: realroots

!Locals
real :: test

test = b**2-4*a*c

if(test>=0.0) then
        root1 = (-b + sqrt(test))/(2.0*a)
        root2 = (-b - sqrt(test))/(2.0*a)
        realroots = .true.
else
        realroots = .false.        
end if

return
end subroutine solvit

Function

program subfunc

implicit none

real :: a,b,c,root1,root2,bigroot
logical :: realroots
write (*,*) "Hello world!"

write (*,10)
read (*,*) a,b,c

!call solvit(a,b,c,root1,root2,realroots)
!write (*,20) root1,root2
write(*,20) bigroot(a,b,c)

if (realroots) then
        write(*,*) 'Sorry, there are no real roots'
end if        

10 format('Enter 3 coefficients')
!20 format('The roots are ', 2f12.6)
20 format('The biggest root is ', f12.6)
end program subfunc

function bigroot(a,b,c)

!Arguments
real :: a,b,c,bigroot

!Local
real :: root1, root2, test

if(test>=0.0) then
        root1 = (-b + sqrt(test))/(2.0*a)
        root2 = (-b - sqrt(test))/(2.0*a)
        if (root1 .gt. root2) then
                bigroot = root1
        else
                bigroot = root2
        end if
else
        bigroot = -9.0e35
end if

return
end function bigroot

Type variables & arrays

Variables

The variable declaration is as such

real            :: x, y
real, parameter :: z
integer         :: m, n
real(8)         :: w
character(len=30) :: frase

Arrays

real, dimension(3) :: vector
real, dimension(3,2) :: matriz3x2
integer, dimension(:)   :: vector-n
integer, dimension(:,:) :: matriz-mxn

!alocação do espaço em memória
allocate(vector-n(21))
allocate(matriz-mxn(4,5))
...
!Limpar a casa no final do programa
deallocate(vector-n)
deallocate(matriz-mxn)

Types

public :: T_Pais
type T_Pais
    character(len=128) :: nome
    character(len=128) :: capital
    integer            :: pop
end type T_Pais

Flow control

If

if (.not. associated(pais)) then
    allocate(pais)
else
    write(*,*) 'The country ', pais%nome, 'is already allocated.'
end if

Do

Loop that increments the counter.

do i=1,10
   write(*,*) 'Couting ',i
end do

Loop that increments the counter by two.

do i=1,21,2
   write(*,*) 'Counting pair ',i-1
end do

Loop that decrements the counter.

do i=20,1,-1
   write(*,*) 'Reverse counting of even ',i*2-1
end do

Samples

Average program

program average
 
  ! Read in some numbers and take the average
  ! As written, if there are no data points, an average of zero is returned
  ! While this may not be desired behavior, it keeps this example simple
 
  implicit none
 
  real, dimension(:), allocatable :: points
  integer                         :: number_of_points
  real                            :: average_points=0., positive_average=0., negative_average=0.
 
  write (*,*) "Input number of points to average:"
  read  (*,*) number_of_points
 
  allocate (points(number_of_points))
 
  write (*,*) "Enter the points to average:"
  read  (*,*) points
 
  ! Take the average by summing points and dividing by number_of_points
  if (number_of_points > 0) average_points = sum(points) / number_of_points
 
  ! Now form average over positive and negative points only
  if (count(points > 0.) > 0) then
     positive_average = sum(points, points > 0.) / count(points > 0.)
  end if
  if (count(points < 0.) > 0) then
     negative_average = sum(points, points < 0.) / count(points < 0.)
  end if
 
  deallocate (points)
 
  ! Print result to terminal
  write (*,'(a,g12.4)') 'Average = ', average_points
  write (*,'(a,g12.4)') 'Average of positive points = ', positive_average
  write (*,'(a,g12.4)') 'Average of negative points = ', negative_average
 
end program average

Other languages

• C/C++
• Perl
• Python
• Ruby