def lcb(fmin, mu, std, kappa=1.96):
    """
    Returns lower confidence bound estimates.
        fmin (float): (not used): Minimum value of the objective function known thus far.
        mu (numpy array):  Mean value of bootstrapped predictions for each y.
        std (numpy array): Standard deviation of bootstrapped predictions for
            each y.
        kappa (float): Controls the variance in the prediction,
            affecting exploration/exploitation.

    Returns:
        vals (numpy array): Acquisition values.
    """
    return mu - kappa * std
