1! { dg-do compile }
2!
3! PR fortran/48800
4!
5! Contributed by Daniel Carrera
6!
7     pure function runge_kutta_step(t, r_, dr, h) result(res)
8         real, intent(in) :: t, r_(:), h
9         real, dimension(:), allocatable :: k1, k2, k3, k4, res
10         integer :: N
11
12         interface
13             pure function dr(t, r_)  ! { dg-error "cannot have a deferred shape" }
14                 real, intent(in) :: t, r_(:)
15                 real :: dr(:)
16             end function
17         end interface
18
19         N = size(r_)
20         allocate(k1(N),k2(N),k3(N),k4(N),res(N))
21
22         k1 = dr(t, r_)
23         k2 = dr(t + h/2, r_ + k1*h/2)
24         k3 = dr(t + h/2, r_ + k2*h/2)
25         k4 = dr(t + h  , r_ + k3*h)
26
27         res = r_ + (k1 + 2*k2 + 2*k3 + k4) * h/6
28     end function
29