def copula_bv_clayton(u, v, theta):
 if (not (theta > 0)):
  raise ValueError('theta needs to be strictly positive')
 return np.power(((np.power(u, (- theta)) + np.power(v, (- theta))) - 1), (- theta))

def copula_bv_clayton ( u , v , theta ) : if ( not ( theta > 0 ) ) : raise ValueError ( 'theta needs to be strictly positive' ) return np . power ( ( ( np . power ( u , ( - theta ) ) + np . power ( v , ( - theta ) ) ) - 1 ) , ( - theta ) )
clayton or cook .