def calculate_alpha(mu1: float, mu2: float, a: float) -> float:
    """
    Args:
        mu1: mean of the first Gaussian random variable :math:`Y_1`
        mu2: mean of the second Gaussian random variable :math:`Y_2`
        a: this number is calculated using standard deviations and the coefficent of linear correlation

    Note:
        alpha can't be calculated in the case :math:`a=0`.
    """
    return (mu2 - mu1) / a