数学附录 9凹函数: Assume that a real- valued function f is defined on a convex set Xc f is said to be concave if for any xand x in X, and any real number nE(0, 1), it holds that (1-)f(x)+^f(x”)≤f(1-)x+x”) f is said to be strictly concave if the sign "<"in the above inequality is replaced by“<”数学附录 • 9 凹函数： Assume that a real-valued function f is defined on a convex set Xn . f is said to be concave if for any x’ and x” in X, and any real number (0, 1), it holds that (1-)f(x’)+f(x”)  f((1-)x’+x”) • f is said to be strictly concave if the sign “” in the above inequality is replaced by “<