# What is the second derivative of a convex function?

## What is the second derivative of a convex function?

What are Convex and Concave Functions? The second derivative of the function depicts how the function is curved, unlike the first derivative which tells us about the slope of the tangent function. A function that has an increasing first derivative bends upwards and is known as a convex function.

Are convex functions monotone?

A differentiable function of one variable is convex on an interval if and only if its derivative is monotonically non-decreasing on that interval.

Is a convex function strictly increasing?

If f is strictly convex, then the first inequality is strict (it’s <). If g is strictly increasing, then that strict inequality is preserved, so h is strictly convex as well. f(tx + (1 − t)y) = A(tx + (1 − t)y) + b = t(Ax + b) + (1 − t)(Ay + b) = tf(x) + (1 − t)f(y).

### Is the second derivative of a convex function positive?

For a twice-differentiable function f, if the second derivative, f ”(x), is positive (or, if the acceleration is positive), then the graph is convex (or concave upward); if the second derivative is negative, then the graph is concave (or concave downward).

Is ex concave or convex?

Example: The graph of ex is always concave up because the second derivative of ex is ex, which is positive for all real numbers. The roots and thus the inflection points are x=0 and x=35. For any value greater than 35, the value of 0″>f′′(x)>0 and thus the graph is convex.

How do you tell if a function is concave or convex?

To find out if it is concave or convex, look at the second derivative. If the result is positive, it is convex. If it is negative, then it is concave.

#### Which is the best description of a convex function?

Here are some of the topics that we will touch upon: \Convex, concave, strictly convex, and strongly convex functions \First and second order characterizations of convex functions \Optimality conditions for convex problems 1 Theory of convex functions 1.1 De\\fnition

Which is the second order characterization of a convex function?

Second order su\cient condition: r2f(x) ˜0; 8×2 )fstrictly convex on : The converse is not true though (why?). First order characterization: A function fis strictly convex on \nif and only if f(y) >f(x) + rfT(x)(y x);8x;y2 ;x6=y: 8 There are similar characterizations for strongly convex functions.

When is a convex function f Rn Ris convex?

A function f: Rn!Ris convex if and only if the function g: R!Rgiven by g(t) = f(x+ ty) is convex (as a univariate function) for all xin domain of f and all y2Rn. (The domain of ghere is all tfor which x+ tyis in the domain of f.)

## Which is an important player in convex optimization?

In this lecture, we shift our focus to the other important player in convex optimization, namely, convex functions.