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Jul
22
comment Fundamental Theorem of Linear Programming
@reuns let's say i got to make a living...
Jul
22
asked Fundamental Theorem of Linear Programming
Jul
16
asked IMO 2015 problem 2
Jul
10
awarded  Popular Question
Jul
10
comment Please show $\int_0^\infty x^{2n} e^{-x^2}\mathrm dx=\frac{(2n)!}{2^{2n}n!}\frac{\sqrt{\pi}}{2}$ without gamma function?
@Sidd yes of course, how silly i were.
Jun
5
asked Please recommend a book/article for Newton-Raphson method
May
18
accepted Why a form is positive only if its matrix in some ordered basis is a positive matrix?
May
18
answered Why a form is positive only if its matrix in some ordered basis is a positive matrix?
May
12
comment What's the maximum speed of snake so that the frog can escape?
@Vim I read Chinese. But the link is about another different problem.
May
12
asked What's the maximum speed of snake so that the frog can escape?
May
11
comment $N^2 = T^*T$, $N$ is non-negative, and $T$ is invertible, how to prove $N$ is also invertible?
thank you, this is correct, i chose the other as the answer as that is what the author use .
May
11
accepted $N^2 = T^*T$, $N$ is non-negative, and $T$ is invertible, how to prove $N$ is also invertible?
May
11
comment $N^2 = T^*T$, $N$ is non-negative, and $T$ is invertible, how to prove $N$ is also invertible?
@Daniel agree with the determinant approach.
May
11
comment $N^2 = T^*T$, $N$ is non-negative, and $T$ is invertible, how to prove $N$ is also invertible?
@aGer sorry i'm stupid. why $\langle N\alpha, N\alpha \rangle - \langle T\alpha, T\alpha \rangle = 0$ leads to that $N$ is invertible?
May
11
asked $N^2 = T^*T$, $N$ is non-negative, and $T$ is invertible, how to prove $N$ is also invertible?
May
5
awarded  Popular Question
May
5
comment How many stones are white?
But why not $105 * \frac{1}{2} - 5 = 47.5$?
May
5
comment Why a form is positive only if its matrix in some ordered basis is a positive matrix?
Could you pls answer the question directly -- that do you think (2) or (4) hold or not?
May
5
comment Why a form is positive only if its matrix in some ordered basis is a positive matrix?
are you sure? Let $B = \begin{bmatrix} 1+i/10 & i/5 \\ -i/5 & 1-i/10 \\ \end{bmatrix}$, is $B$ Hermitian? $B^* = \begin{bmatrix} 1-i/10 & i/5 \\ -i/5 & 1+i/10 \\ \end{bmatrix}$, apparently $B^* \ne B$.
May
4
asked How many stones are white?