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Real-valued functions of real variable, analytic properties of functions and sequences, limits, continuity, smoothness of these.

3 votes
2 answers
384 views

On the regularity of certain continuous algebraic functions

Let $\mathcal{C}$ be the class of continuous functions that— map $[0, 1]$ to $[0, 1]$, and equal neither 0 nor 1 on the open interval $(0, 1)$. A function $f(x)$ is algebraic over the rational numbe …
Peter O.'s user avatar
  • 697
3 votes
1 answer
227 views

Explicit bounds on the difference between Bernstein polynomials

Let $f:[0,1]\to [0,1]$ be continuous. Let— $$B_n(f)(x)=\sum_{k=0}^n f(k/n) {n \choose k} x^k (1-x)^{n-k},$$ be the Bernstein polynomial of $f$ of degree $n$. This question relates to the difference b …
Peter O.'s user avatar
  • 697
3 votes

Explicit and fast error bounds for polynomial approximation

After analyzing the proof of Güntürk and Li (2021), Theorem 2.4, I believe I found explicit error bounds for the Micchelli–Felbecker polynomials (iterated Bernstein polynomials) when $f(x)$ has a giv …
Peter O.'s user avatar
  • 697
6 votes
0 answers
403 views

Using the Lorentz operators to build polynomials that converge to a continuous function

Questions Let $f(\lambda):[0,1]\to (0,1)$ have a $\beta-\lfloor\beta\rfloor$)-Hölder continuous $\lfloor\beta\rfloor$-th derivative, where $\beta>0$. Find explicit bounds, with no hidden constants, o …
Peter O.'s user avatar
  • 697
17 votes
2 answers
2k views

Explicit and fast error bounds for polynomial approximation

Main Question This question is about finding explicit, calculable, and fast error bounds when approximating continuous functions with polynomials to a user-specified error tolerance. EDIT (Apr. 23): …
Peter O.'s user avatar
  • 697
4 votes
1 answer
624 views

Explicit and fast error bounds for approximating continuous functions

Main Question This question is about finding explicit, calculable, and fast error bounds (no hidden constants) when approximating continuous functions with polynomials or simpler functions to a user-s …
Peter O.'s user avatar
  • 697
2 votes

Explicit and fast error bounds for approximating continuous functions

Here are some results on certain polynomials. Tachev (2022)[^4] has published an error bound that relates to the polynomial— $$L_{2,n/2} = 2B_n(f) - B_{n/2}(f).$$ Their Theorem 2 describes the bound p …
Peter O.'s user avatar
  • 697
8 votes
0 answers
515 views

Concave and other bounded functions: Series representation and converging polynomials

Main Question Suppose $f:[0,1]\to[0,1]$ is continuous, polynomially bounded, and belongs to a large class of functions (for example, the $k$-th derivative, $k\ge 0$, is continuous, Lipschitz continuou …
Peter O.'s user avatar
  • 697