Function 5(6) with a p-dimensional vector 19 is maximised at g if am) 0'6}- =0forj=1,...,pand a. All the elements of the observed information matrix JG), 3/) are positive. '13- All the elements of the observed information matrix J (, y) are negative. 0- The observed information matrix Kg, y) is negative definite. d- The observed information matrix J (, y) is positive definite