How can I show that a twice continuously differentiable function with a lipschitz continuous hessian with all eigenvalues≥mu is mu strongly convex?

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How can I show that a twice continuously differentiable function with a lipschitz continuous hessian with all eigenvalues≥mu is mu strongly convex?

Definition 2.2. A function f : R" → R is said to be u-strongly convex if
38
Vx, y E R" :
f (x) + (Vf(x), y – x) + y – x||² < f(y)
(2.4)
Transcribed Image Text:Definition 2.2. A function f : R" → R is said to be u-strongly convex if 38 Vx, y E R" : f (x) + (Vf(x), y – x) + y – x||² < f(y) (2.4)
Definition (Lipschitz continuity)
Suppose that
• X and y open sets
• F: X →Y
• || · ||x and || · ||y are norms
Then
• F is Lipschitz continuous at x E X if 3 y(x) such that
|F(z) - F(x) ||ly < Y(x) ||z-제1x
for all z E X.
• F is Lipschitz continuous throughout/in X if 3 y such that
||F(2) – F(x)||» < l|z – x|| x
for all x and z E X.
Theorem (Taylor approximations for real-valued functions)
Let S be an open subset of R", s E R", and suppose that f : S → R is continuously
differentiable throughout S and g = Vf is Lipschitz continuous at x with Lipschitz
constant y (x) for some appropriate vector norm. It follows that if the segment
[x, x + s] E S, then
\F(x + s) – m“ (x + s)| < (x)|||°,
where
m" (x + s) = f(x) +g(x)*s.
If in addition, f is twice continuously differentiable throughout S and H =
Lipschitz continuous at x, with Lipschitz constant y (x), then
= V²f is
F(x + s) – mº (x + s)| < e (x)||s||°,
where
m° (x + s) = f(x) + 8(x)"s + }s'H(x)s.
Transcribed Image Text:Definition (Lipschitz continuity) Suppose that • X and y open sets • F: X →Y • || · ||x and || · ||y are norms Then • F is Lipschitz continuous at x E X if 3 y(x) such that |F(z) - F(x) ||ly < Y(x) ||z-제1x for all z E X. • F is Lipschitz continuous throughout/in X if 3 y such that ||F(2) – F(x)||» < l|z – x|| x for all x and z E X. Theorem (Taylor approximations for real-valued functions) Let S be an open subset of R", s E R", and suppose that f : S → R is continuously differentiable throughout S and g = Vf is Lipschitz continuous at x with Lipschitz constant y (x) for some appropriate vector norm. It follows that if the segment [x, x + s] E S, then \F(x + s) – m“ (x + s)| < (x)|||°, where m" (x + s) = f(x) +g(x)*s. If in addition, f is twice continuously differentiable throughout S and H = Lipschitz continuous at x, with Lipschitz constant y (x), then = V²f is F(x + s) – mº (x + s)| < e (x)||s||°, where m° (x + s) = f(x) + 8(x)"s + }s'H(x)s.
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