def euler(initial, tendency, h=1):
    """Integrate forward in time using Euler's method of numerical integration.
    initial + h*tendency

    Arguments
    ---------
    initial :  float
        The initial state.
    tendency : float
        The rate of change in the initial state.

    Keyword arguments
    -----------------
    h = 1 : float
        The timestep duration.
    """
    return initial + h*tendency