def getPreviousTimeStep(cycle, node, burnSteps):
    """Return the time step before the specified time step"""
    if (cycle, node) == (0, 0):
        raise ValueError("There is not Time step before (0, 0)")
    if node != 0:
        return (cycle, node - 1)
    else:
        # index starts at zero, so the last node in a cycle is equal to the number of
        # burn steps.
        return (cycle - 1, burnSteps)