Jk. Chung et al., ON A FUNCTIONAL-EQUATION CONNECTED WITH RAO QUADRATIC ENTROPY, Proceedings of the American Mathematical Society, 120(3), 1994, pp. 843-848
We determine the general solution of the functional equation f(x+y/2)f(x-y/2) = 2f(x/2)+2f(y/2) + lambdaf(x)f(y), for f : [-1, 1] --> R. Th
is equation was used by Lau in order to characterize Rao's quadratic e
ntropies. The general solution is obtained here as a special case of a
mom general result for f mapping a neighborhood of 0 in a linear topo
logical space into a field.