Question

This is almost trivial with the Fortran Magic extnesion.

! pip install fortran-magic &> /dev/null

%load_ext fortranmagic

%%fortran

subroutine fib3(n, a)
    integer, intent(in) :: n
    real, intent(out) :: a

    integer :: i
    real :: b, tmp

    a = 0
    b = 1
    do i = 1, n
        tmp = b
        b = a
        a = a + tmp
    end do
end subroutine

fib3(100)

354224717716315439104.0000

Antoher example from the documentation

%%fortran --link lapack

subroutine solve(A, b, x, n)
    ! solve the matrix equation A*x=b using LAPACK
    implicit none

    real*8, dimension(n,n), intent(in) :: A
    real*8, dimension(n), intent(in) :: b
    real*8, dimension(n), intent(out) :: x

    integer :: pivot(n), ok

    integer, intent(in) :: n
    x = b

    ! find the solution using the LAPACK routine SGESV
    call DGESV(n, 1, A, n, pivot, x, n, ok)

end subroutine

A = np.array([[1, 2.5], [-3, 4]])
b = np.array([1, 2.5])

solve(A, b)

array([-0.1957,  0.4783])