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! { dg-do compile }
!
! PR fortran/48800
!
! Contributed by Daniel Carrera
!
pure function runge_kutta_step(t, r_, dr, h) result(res)
real, intent(in) :: t, r_(:), h
real, dimension(:), allocatable :: k1, k2, k3, k4, res
integer :: N
interface
pure function dr(t, r_) ! { dg-error "cannot have a deferred shape" }
real, intent(in) :: t, r_(:)
real :: dr(:)
end function
end interface
N = size(r_)
allocate(k1(N),k2(N),k3(N),k4(N),res(N))
k1 = dr(t, r_)
k2 = dr(t + h/2, r_ + k1*h/2)
k3 = dr(t + h/2, r_ + k2*h/2)
k4 = dr(t + h , r_ + k3*h)
res = r_ + (k1 + 2*k2 + 2*k3 + k4) * h/6
end function
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