Math 2.0

Approximations and expansions Definition

Bernstein polynomial

Definition

Let f ⁣:[0,1]→ℝf \colon [0, 1] \to \mathbb{R} be a function and let n≥1n \ge 1 be an integer. The nn-th Bernstein polynomial of ff is Bn(f)(x)=∑k=0nf(kn)(nk)xk(1−x)n−k.B_n(f)(x) = \sum_{k=0}^{n} f\Big( \frac{k}{n} \Big) \binom{n}{k} x^k (1 - x)^{n-k}. The polynomials bk,n(x)=(nk)xk(1−x)n−kb_{k,n}(x) = \binom{n}{k} x^k (1 - x)^{n-k} are the Bernstein basis polynomials.

Remarks

If ff is continuous, then Bn(f)→fB_n(f) \to f uniformly on [0,1][0, 1]. This proves the Weierstrass approximation theorem. The basis polynomials are nonnegative on [0,1][0, 1], and they sum to 11 by the binomial theorem. Sergei Bernstein gave this proof in 1912, with an argument from probability. Mathlib defines the basis polynomials as bernsteinPolynomial.

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Further reading

  1. Web https://en.wikipedia.org/wiki/Bernstein_polynomial, Definition
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