Mehrstellenverfahren for the Poisson equation

high_order_poisson_solver.f90

! See link below for details:
! https://scicomp.stackexchange.com/questions/6854/mehrstellenverfahren-for-poisson
!
program poisson_higher_order

    implicit none

    integer, parameter :: wp = kind(1.0d0)
    real(wp), parameter :: pi = 4._wp*atan(0._wp)

contains

    pure real(wp) function f(x)
        real(wp), intent(in) :: x

        f = sin(2._wp*pi*x)
    end function

end program