 Formation matrix

In statistics and information theory, the expected formation matrix of a likelihood function formula_1 is the matrix inverse of the Fisher information matrix of formula_1, while the observed formation matrix of formula_1 is the inverse of the observed information matrix of formula_1.Currently, no notation for dealing with formation matrices is widely used, but in books and articles by Ole E. Barndorff-Nielsen and Peter McCullagh, the symbol formula_5 is used to denote the element of the i-th line and j-th column of the observed formation matrix.