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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
Sep
10
awarded  Popular Question
Jul
15
revised Expected value and the standard simple regression model
typo in the title
Jul
15
suggested approved edit on Expected value and the standard simple regression model
Jul
15
comment What are the general steps to turn a PDE into a dynamical system $\dot x(t)= Ax(t) + Bu(t)$
Check textbooks on control theory. The wiki page may also help: en.wikipedia.org/wiki/State-space_representation
May
17
awarded  Yearling
Apr
24
revised Calculating $a_n$ in $\sum_{n=1}^\infty a_n \sin(\frac{n \pi}{2})=T_0$
() -> \left(\right)
Apr
24
suggested approved edit on Calculating $a_n$ in $\sum_{n=1}^\infty a_n \sin(\frac{n \pi}{2})=T_0$
Apr
10
comment How many distinct elements are there in $C=\{zw\mid z∈A$,$w∈B\}, z^{24}=1$ and $w^{54}=1$.
But this is anyway an algebra problem.
Apr
8
revised Why are additional constraint and penalty term equivalent in ridge regression?
deleted 8 characters in body
Apr
7
revised Why are additional constraint and penalty term equivalent in ridge regression?
added 748 characters in body
Apr
7
revised The positive-definite-ness of RBF kernel
deleted 5 characters in body
Apr
6
revised Why are additional constraint and penalty term equivalent in ridge regression?
added 17 characters in body
Apr
6
answered Why are additional constraint and penalty term equivalent in ridge regression?