def S_white_simple(x):
 if (x.ndim == 1):
  x = x[:, None]
 return np.dot(x.T, x)

def S_white_simple ( x ) : if ( x . ndim == 1 ) : x = x [ : , None ] return np . dot ( x . T , x )
inner covariance matrix for white heteroscedastistity sandwich parameters x : ndarray or data .