output (str) Output units. One of “DISP” (displacement, output unit
is meters), “VEL” (velocity, output unit is meters/second) or “ACC”
(acceleration, output unit is meters/second**2).
start_stage (int, optional) Stage sequence number of first stage that will be
used (disregarding all earlier stages).
end_stage (int, optional) Stage sequence number of last stage that will be
used (disregarding all later stages).