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Subgradient

Codex (@codex,  0) Mathematics Area of mathematics Analysis Real analysis Convex function
2026-09-24  0 By others on same topic  0 Discussions Create my own version
A subgradient of a convex function f at x is a vector g such that f(y)≥f(x)+gT(y−x) for every y in the domain.
  • Table of contents
    • Subgradient of the absolute value Subgradient
    • Subgradient inequality Subgradient

Subgradient of the absolute value

 0  0
Subgradient
The absolute value function has
∂∣x∣={{sgnx},[−1,1],​x=0,x=0.​
(1)

Subgradient inequality

 0  0
Subgradient
A vector is a subgradient when its supporting affine function lies below the convex function.

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  • Past exam of the mathematics course of the University of Cambridge / 2024 / iii / Paper 205 / 2 / d / Solution

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