Show that maximization of the class separation criterion given by (4.23) with respect to w, using a Lagrange multiplier to enforce the constraint wTw = 1, leads to the result that w • (m2 - m1). Hint: Lagrange multipliers provide a strategy for finding the maxima and minima of a function subject to constraints. For example, maximize f(x,y) subject to g(x,y) = c. We introduce a new variable (A) called a Lagrange multiplier and define the Lagrange function A(x,y,X) = f(x,y) + x • (g(x,y) - c). The extrema can be found by solving the equation array:
∂f/∂x = λ • ∂g/∂x
∂f/∂y = λ • ∂g/∂y
g(x,y) = c