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 Yearling
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May
5
answered Find density function of $X + Y$ , where $X, Y$ random variables.
May
5
comment Problem with the Birthday Problem
your approach if fundamentally wrong.
May
2
reviewed Approve Why is $z^4-1-i=0$ a polynomial equation which does not have real coefficients?(complex-number)
May
2
reviewed Approve Orthogonal complement of orthogonal complement
Apr
30
comment Joint density function N
joint density says that they are..
Apr
30
comment Joint density function N
$X_i$ are Gaussian distributed, because they are jointly Gaussian distributed. Then fullstop. One needs to know if $X_i$ are independent or not.
Apr
30
comment Joint density function N
First of all what is the distribution of $Y$?
Apr
27
comment Is the axiom of choice really all that important?
populist question.
Apr
27
reviewed Approve Eigenvalues and eigenvectors for orthogonal projection
Apr
27
reviewed Reject Diagonalization and $T(f(t))=f(t+1)$
Apr
26
comment A short question about the convexity of a function
okay it seems above, it is not guaranteed to be greater than zero because $f^{''}(x)>0$, $r^{'}(f(x))<0$, and $r^{''}(f(x))>0$ and $f^{'}(x)^2>0$.
Apr
26
comment A short question about the convexity of a function
Yes but concave or convex? I did this: $h=r(f(x))$ for $r=g^{-1}$ and $f=1-g$. Then $h^{''}(x)=r^{''}(f(x))f^{'}(x)^2+r^{'}(f(x))f^{''}(x)>0$, so $h$ is convex. Is what I did actually trivial? cannot $f(x)$ change the function from convex to concave?
Apr
26
comment A short question about the convexity of a function
Jack, sorry it is probably a bit late but I am trying understand the conclusion of your answer and I am confused in the last parts. Until $(1)$, everything is okay. First, why should $(1)$ imply that if $h(x)$ in a small neighborhood of $1$ is convex, then $h(x)$ is convex on $[0,1]$? I understood $h(x)$ around $1$ is the same with $g$ around $0$. Then $g$ is concave around $0$, so $f=1-g$ is convex, which is fine. Then, $h=g^{-1}(f)$ is convex but how? Is it true that decreasing function of a convex function is convex? Could you please help me understand these two points? thanks in advance.
Apr
26
reviewed Approve mensuration-Surfaces area and volumes
Apr
26
revised Is the given binomial sum almost everywhere negative as $K\to\infty$?
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Apr
25
awarded  Yearling
Apr
23
comment Random variable with infinite expectation
@did just a suggestion. I mean it is the choice of OP but there may be also other people who can appreciate other answers too, I would personally)
Apr
23
comment Random variable with infinite expectation
@did why dont you write it as an answer? dont you think that is seems ugly as a comment?
Apr
23
answered Negative binomial distribution pmf derivative
Apr
23
revised Econometrics/Statistics, variance and means
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