nderivatives

Nderivatives, in mathematical usage, refers to the nth derivatives of a function. They generalize the concept of a first derivative to higher orders and describe the successive rates of change of a function’s rate of change. The nth derivative of a function f is commonly denoted f^(n)(x) or d^n f/dx^n. Existence requires that f be differentiable up to order n on the interval of interest.

For a basic example, if f(x) = x^m with m a nonnegative integer, then f^(n)(x) = m(m−1)…(m−n+1) x^{m−n} for n ≤ m, and f^(n)(x) = 0 for n > m. Polynomials of degree d have all derivatives of order greater than d equal to zero.

Key properties of nderivatives include linearity: (a f + b g)^(n) = a f^(n) + b g^(n). The nth derivative of a product satisfies the generalized Leibniz rule: (f g)^(n) = sum_{k=0}^n binomial(n, k) f^(k) g^(n−k). Derivatives of compositions are governed by Faà di Bruno's formula, a combinatorial extension of the chain rule.

In several variables, first derivatives form the gradient, second derivatives form the Hessian, and higher-order derivatives are symmetric tensors of order n, with mixed partial derivatives commuting under suitable regularity (Clairaut’s theorem).

Applications of nderivatives include Taylor series expansions, physics and engineering modeling, and numerical analysis, where derivatives are approximated by finite difference methods. The study of higher-order derivatives connects to topics such as differential equations, approximation theory, and differential geometry.