(A, AB, B)
return np.mean(B * (AB - A), axis=0) / np.var(np.r_[A, B], axis=0)
First order estimator following Saltelli et al. 2010 CPC, normalized by
    sample variance
First order estimator following Saltelli et al. 2010 CPC, normalized by
    sample variance
First order estimator following Saltelli et al . 2010 CPC normalized by sample variance
def first_order(A, AB, B):
    """
    First order estimator following Saltelli et al. 2010 CPC, normalized by
    sample variance
    """
    return np.mean(B * (AB - A), axis=0) / np.var(np.r_[A, B], axis=0)
def first_order ( A , AB , B ) : return np . mean ( B * ( AB - A ) , axis = 0 ) / np . var ( np . r_ [ A , B ] , axis = 0 )