하방미분

Also known as subdifferential, subgradient

right|thumb|A convex function (blue) and "subtangent lines" at x_0 (red). In mathematics, the subderivative (or subgradient) generalizes the derivative to convex functions which are not necessarily differentiable. The set of subderivatives at a point is called the subdifferential at that point. Subderivatives arise in convex analysis, the study of convex functions, often in connection to convex optimization.