gcc/testsuite/gfortran.dg/import9.f90

   1 ! { dg-do compile }
   2 !
   3 ! PR fortran/48821
   4 !
   5 ! Contributed by Daniel Carrera
   6 !
   7
   8 contains
   9      pure subroutine rk4_vec(t, Y, dY, h)
  10          real, intent(inout) :: t, Y(:)
  11          real, intent(in) :: h
  12          real, dimension(size(Y)) :: k1, k2, k3, k4
  13
  14          interface
  15              pure function dY(t0, y0)
  16                  import :: Y
  17                  real, intent(in) :: t0, y0(size(Y))
  18                  real :: dY(size(y0))
  19              end function
  20          end interface
  21
  22          k1 = dY(t, Y)
  23          k2 = dY(t + h/2, Y + k1*h/2)
  24          k3 = dY(t + h/2, Y + k2*h/2)
  25          k4 = dY(t + h  , Y + k3*h)
  26
  27          Y = Y + (k1 + 2*k2 + 2*k3 + k4) * h/6
  28          t = t + h
  29      end subroutine
  30 end