| ! { 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 |
