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

14 votes

Which functions have all derivatives everywhere positive?

Well, there are certainly more. If you look at the chain rule then you see that the $n$-th derivative is a linear combinations of products of derivatives of the two functions you compose with positive …
Stefan Waldmann's user avatar
11 votes
3 answers
2k views

Hilbert's 17th Problem for smooth functions

Consider an open subset $U \subseteq \mathbb{R}^n$ and a smooth function $f\colon U \longrightarrow \mathbb{R}$ with $f(x) \ge 0$ for all $x \in U$. It is then known (if I remember correctly: by Mich …
Stefan Waldmann's user avatar
8 votes
Accepted

Is there dual space of the distributions $\mathcal{D}'(R)$?

Well, that depends on what topology you want to put on the space of distributions. The weak$^*$ is probably not really the one you would like to take. Instead, the strong dual might be more useful. Th …
Stefan Waldmann's user avatar
6 votes

analysis over non-Archimedean ordered fields

Well, there seems to be a lot of literature. I have encountered similar questions once when discussing problems in deformation quantization. here the ordered field is simply the field of formal Lauren …
Stefan Waldmann's user avatar