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

2 votes

Monotonicity of the sequences of the lower and upper Darboux sums

This is a long comment to @AnthonyQuas's solution. It works out the details of the stochastic dominance as stated by Anthony. Let $F_n(x) = \int_{-\infty}^x \,d\mu^+_n(t)$ be the cumulative distrib …
VictorZurkowski's user avatar
2 votes

Checking $f(x_1,y_1)f(x_2,y_2)-f(x_1,y_2)f(x_2,y_1) \ge 0$

To follow up @igor answer, the equation can be written as: $$ \dfrac{\partial^2 \ln f}{\partial x \partial y} \geq 0. $$ Moreover, the inequality is not only necessary, bu sufficient, since: $$ \ln \ …
VictorZurkowski's user avatar
1 vote
Accepted

Smooth Approximation of Indicator Function of Convex Sets in $\mathbb{R}^n$

Let's pursue Jochen's idea. We assume $A \ne \emptyset.$ Let $$ \varphi(t) = \begin{cases} e^{-\frac{1}{t}} &\text{if $ t>0$}\\ 0 &\text{otherwise.} \end{cases}$$ This func …
VictorZurkowski's user avatar
0 votes

Is the domain of symmetric derivative borel set?

We can majorize $\lambda $ by a non-negative Borel measure $|\lambda|$. Let $\nu = |\lambda| + \mu .$ Since $|\lambda|$ and $\mu$ are absolutly continuos with respect to $\nu$, we can represent $\lam …
VictorZurkowski's user avatar