## ABSTRACT

If A is a matrix with elements that are differentiable functions of the scalar variable x, and has an inverse matrix A−1 for any x, then the derivative of the inverse matrix is given by

dx dx

= − A A

A A

(17.17)

Equation 17.17 is obtained by differentiating the identify AA−1 = I, where I is the identity matrix. Fröberg (1965, p. 71).