False-negatives
    
    Parameters:
    -----------
    y : vector, shape (n_samples,)
    The target labels.

    y_pred : vector, shape (n_samples,)
    The predicted labels.
    
    Returns:
    --------
    fn : integer, the number of false-negatives

def false_negatives(y, y_pred):
    """False-negatives
    
    Parameters:
    -----------
    y : vector, shape (n_samples,)
    The target labels.

    y_pred : vector, shape (n_samples,)
    The predicted labels.
    
    Returns:
    --------
    fn : integer, the number of false-negatives
    
    """

    y, y_pred = convert_assert(y, y_pred)
    assert_binary_problem(y)

    return np.count_nonzero(y_pred[y == 1] == 0)