Total derivative in finite dimensions
Differentiability means a linear approximation with smaller-order error.
Key knowledge
For f:U⊂Rⁿ→Rᵐ with U open, f is differentiable at a if a linear map B satisfies ‖f(a+h)−f(a)−Bh‖/‖h‖→0 as h→0. This B is the total derivative Df(a).
Values and equations
limₕ→₀ ‖f(a+h)−f(a)−Df(a)h‖/‖h‖ = 0
- f
- Map from an open subset of Rⁿ to Rᵐ
- Df(a)
- Linear derivative
- h
- Nonzero increment approaching zero
Conditions and scope
- a is an interior point and h≠0 in the limit.
- Existence of all partial or directional derivatives alone is insufficient.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Definition 2.3 and Theorem 2.4: total derivative as a linear approximation; directional derivatives alone insufficient.
2026-10-10 · Finite-dimensional total derivative, Definition 2.3.
Entry details
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- math-multivariable-differentiation
- Revision
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- Structured reference record
- University reference