ComputeLightTravelTime - function to compute light travel time between
	two GW detectors at positions Det1Pos and Det2Pos.

	Det1Pos - (3,) array. Position vector of detector 1.
	Det2Pos - (3,) array. Position vector of detector 2.

	Returns travelTime - Light travel time between two GW detectors at
			     positions Det1Pos and Det2Pos [s].

        Sarah Gossan 2012. Adapted from TimeDelay.c, written by Jolien
	Creighton, David Chin, Steven Fairhurst, Kipp Cannon, Alexander Dietz, 
	Drew Keppel 2007.

def ComputeLightTravelTime(Det1Pos, Det2Pos):
    """ ComputeLightTravelTime - function to compute light travel time between
	two GW detectors at positions Det1Pos and Det2Pos.

	Det1Pos - (3,) array. Position vector of detector 1.
	Det2Pos - (3,) array. Position vector of detector 2.

	Returns travelTime - Light travel time between two GW detectors at
			     positions Det1Pos and Det2Pos [s].

        Sarah Gossan 2012. Adapted from TimeDelay.c, written by Jolien
	Creighton, David Chin, Steven Fairhurst, Kipp Cannon, Alexander Dietz, 
	Drew Keppel 2007."""

    # Get relative position vector
    Det21Pos = Det2Pos - Det1Pos
  
    # Dot difference vector into itself to get magnitude of detector separation
    dist = np.sqrt(np.dot(Det21Pos,Det21Pos))

    # Normalise with speed of light
    travelTime = dist/c

    return travelTime