Alphabeta Math

Convexity: Examples and Counterexamples

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1 · Prerequisites
2 · Logical flowchart

3 · Items

Example

The absolute-value function is convex

Example

Finite Jensen for x↦ x² gives that the square of a weighted mean is at most the weighted mean of the squares

Counterexample

Assuming Choice, a Hamel coefficient map is midpoint convex but discontinuous and therefore not convex

Example

x↦ x³ changes from concave to convex at zero and has an inflection point there

Sources