!
!       project "gravity field"
!
!-----------------------------------------------------------------------
module realfield
  implicit none

!-----------------------------------------------------------------------
!      definition of structures
!
type massbody
  real                  :: posx, posy
  real                  :: mass          = 1.0
  integer               :: serial        = 666
end type

!-----------------------------------------------------------------------
contains
!-----------------------------------------------------------------------

function compute_gravity(fx, fy, body)
  real, intent(in)              :: fx, fy
  type(massbody), intent(in)    :: body
  real                          :: compute_gravity
  real                          :: rx, ry, dist

  rx = fx - body%posx
  ry = fy - body%posy
  dist = sqrt( (rx*rx) + (ry*ry) )
  if (dist .LT. 4.50) then
    write (0, *) "dist too small ", dist
    compute_gravity = 0e0
  endif
  compute_gravity = body%mass / (dist ** 2)

end function

!-----------------------------------------------------------------------
!-----------------------------------------------------------------------

end module