3 Strongly Convex Functions on Inner Pro-
duct Spaces
Here we state and prove our main results, those are similar to the case on real
intervals but now on inner product spaces. First we recall some facts about
derivatives on normed spaces; let X and Y be normed spaces, g : U ⊆ X → Y
a function and U an open subset. Then g is said to be differentiable at x0 ∈ U
if there exists a linear transformation S : X → Y such that, for h ∈ X small
enough,
g(x0 + h) = g(x0) + S(h) + ||h||ǫ(x0, h),
where ǫ(x0, h) ∈ Y and goes to zero as ||h|| → 0. This linear transformation
is called the derivative and is denoted by g
′
(x0). It is worth to notice that we