def split_shape(shape):
	"""Splits a shape into its ringlet shape and frame shape
	E.g., (2,3,-1,4,5) -> (2,3), (4,5)
	"""
	ringlet_shape = []
	for i,dim in enumerate(shape):
		if dim == -1:
			frame_shape = shape[i+1:]
			return ringlet_shape, frame_shape
		ringlet_shape.append(dim)
	raise ValueError("No time dimension (-1) found in shape")