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Jan
29
comment Why is a vector function not smooth if $r'=0$
It's like you walk, stop, and (probably turn and) walk again. There will a singularity in the route.
Jan
17
comment Laplace, Legendre, Fourier, Hankel, Mellin, Hilbert, Borel, Z…: unified treatment of transforms?
@Startwearingpurple Can separable Hilbert space have uncountable orthonormal basis?
Jan
15
revised Different versions of Mercer's theorem
deleted 1 character in body
Jan
15
asked Different versions of Mercer's theorem
Jan
12
revised Continuity of a Linear function
For grammar mistakes
Jan
12
comment When do matrices have positive eigenvectors?
What's a positive eigenvector?
Jan
12
suggested approved edit on Continuity of a Linear function
Jan
12
revised When do matrices have positive eigenvectors?
For grammar mistakes
Jan
12
suggested approved edit on When do matrices have positive eigenvectors?
Jan
11
revised About sequential weak closure in $\ell^2$
Texified the title; <> t0 langle/rangle
Jan
11
comment Prove that $(a-b)^n\mid (a^n-b^n) \iff n=1$ under given conditions
Why is it the hardest?
Jan
11
suggested approved edit on About sequential weak closure in $\ell^2$
Jan
11
comment Find the sum $\sum_{k=2}^n \frac{n!}{(n-k)!(k-2)!}.$
$LHS=\frac{n!}{(n-2)!}\sum_{k=0}^{n-2}\frac{(n-2)!}{(n-2-k)!k!}=n(n-1)2^{n-2}$
Jan
7
comment Show that $rank(A) \ngeq \frac{[tr(A)]^2 }{tr(A^2)}$
Does >/= mean <?
Jan
6
answered $E(X\mid X+Y)$, where $X$ and $Y$ are independent $U(0,1)$.
Dec
7
awarded  Announcer
Dec
3
awarded  Nice Question
Oct
2
comment Every convex function is continuous
@RFZ any $t<u_1<b$ and $a<u_2<s$ are OK.
Oct
2
comment Every convex function is continuous
There is $u_1$ such that $f(t)-f(s)\le\frac{f(u_1)-f(t)}{u_1-t}(t-s)=L_1(t-s)$. Similarly there is $u_2$ such that $f(t)-f(s)\ge\frac{f(t)-f(u_2)}{t-u_2}(t-s)=L_2(t-s)$. So $|f(t)-f(s)|\le L|t-s|$ for some $L$.
Sep
30
revised Similarity between $I+N$ and $e^N$ when $N$ is nilpotent
less verbose