(In reply to

re: Analytical solution (spoiler) by Charlie)

Oops. sorry, misread it. Let's try again:

(1) a + b = ab

(2) solving for b, we get b = a/(a-1)

Then ab = a*a/(a-1)

(3) Let c = (a+1)

Then ab = (c+1)*(c+1)/c = c + 2 + 1/c

Derivative (with respect to c) = 1 - 1/(c*c)

Setting this equal to 0 and solving gives c = 1

So, local minimum occurs when ab = 1 + 2 + 1/1 = 4