! 2.4.f90
! $Id: 2.4.f90 1.3 2025/07/13 09:40:04 s Exp $
!
module subprog
    implicit none
contains
    function f(x) result(v)
        real(8), intent(in) :: x
        real(8) v
        v = -1.0d0 + x + x ** 2
    end
    function fd(x) result(v)
        real(8), intent(in) :: x
        real(8) v
        v = 1.0d0 + 2.0d0 * x
    end
end module subprog

program ex2_4
use subprog
real(8) x0, x1, x2, x3, x4
character * 10 keisen
keisen = '----------'

! calculation
x0 = 1.0d0
x1 = x0 - f(x0) / fd(x0)
x2 = x1 - f(x1) / fd(x1)
x3 = x2 - f(x2) / fd(x2)
x4 = x3 - f(x3) / fd(x3)

! output
write(*,*) '2.4.f90'
write(*,'(4a10)') 'k', 'x', 'f(x)', "f'(x)"
write(*,'(4a10)') keisen, keisen, keisen, keisen
write(*,'(i10,3f10.7)') 0, x0, f(x0), fd(x0)
write(*,'(i10,3f10.7)') 1, x1, f(x1), fd(x1)
write(*,'(i10,3f10.7)') 2, x2, f(x2), fd(x2)
write(*,'(i10,3f10.7)') 3, x3, f(x3), fd(x3)
write(*,'(i10,3f10.7)') 4, x4, f(x4), fd(x4)
write(*,'(4a10)') keisen, keisen, keisen, keisen
end program ex2_4
! end of 2.4.f90