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Aug
25
comment As of August 2015, is the “set” of all gold medalists in the 2016 Olympics a set?
I believe at present the set is empty. Next year its cardinality may change.
Aug
15
comment L'Hôpital or L'Hospital?
You can italicize text by using asterisks (like *this*) which is better than pretending it is mathematics.
Aug
15
comment What type of diagram could this be?
en.wikipedia.org/wiki/Penrose_graphical_notation ?
Aug
14
comment How to design/shape a polyhedron to be nearly spherically symmetrical, but not a platonic solid?
@columbus8myhw: Euler's formula totally applies to things with holes, it's just that the right-hand side becomes $2-2g$, where $g$ is the number of holes. See Euler characteristic.
Aug
6
comment When does one vector has bigger norm than the other?
It's not possible that $u_k < v_k$ for all $k$, because then $u$ and $v$ would not both have components summing up to $1$. So your proposed sufficient condition just reduces to $u = v$.
Aug
6
comment Analytic Center of Convex Polytope
Boyd and Vandenberghe's book Convex Optimization defines the analytic center of a set of convex inequalities and linear equalities in Sec. 8.5.3. It is equivalent to the definition in Mihir's comment. Note that two different sets of inequalities that define the same polytope can have different analytic centers.
Jul
31
comment Integrate area of function over a tetrahedron
The limits of the innermost integral are the limits of which variable?
Jul
31
comment Why prove that area is unique?
What we're worried about is not that the area might not be unique, but that our inequalities might not be strong enough to nail it down. For example, one can easily show that the area must satisfy $0 < A < b^3$. Now by your logic, I could say that $b^3/2$ satisfies those inequalities, and the area is clearly unique, so we must have $A = b^3/2$.
Jul
31
comment How many minimally sides are needed to fully enclose a volume in an $n$-dimensional spaece?
Excuse me, it's Bender Bending Rodríguez. :)
Jul
31
comment convex relaxations
Actually, are you sure $\|x\|_2\|x\|_1$ is nonconvex?
Jul
30
comment Is $e^x$ finite almost everywhere even though $\mathop {\lim }\limits_{x \to \infty } {e^x} = + \infty $?
I think that first "blah everywhere" should be "blah almost everywhere".
Jul
30
comment Vibrating water container problem
This is a poorly designed problem. The water cannot jump up like that because below it there would be a vacuum. In real life the behaviour of water in a vertically oscillating container is surprisingly complicated.
Jul
30
comment Maximization of sum of functions
If you say so. But the maximum can't be unique because $f(\alpha w)=f(w)$ for all $\alpha\ne0$.
Jul
30
comment Maximization of sum of functions
Let $a=(1,0)$, $B=I_{2\times 2}$. Then $f(x,y)=x^2/(x^2+y^2)$ is concave in $(x,y)$?
Jul
30
comment What is the highest number that can be got from 4383 by moving exactly 2 matches?
An LED-style 9 is supposed to have the bottom horizontal bar. What you have there looks more like a q.
Jul
30
comment What is the value of $\lim_{x\to 0}x^x$?
No, $x\ln x\ne\ln x+1$.
Jul
29
comment What is the formal negation of the statement “There is much X in Y”.
There isn't much X in Y.
Jul
28
comment How can I use the Bullet-Physics's ray-cast normal to calculate angles for a object to lay on a surface?
Does this previous post answer your question?
Jul
27
comment How can I use the Bullet-Physics's ray-cast normal to calculate angles for a object to lay on a surface?
So... you want to rotate the pizza so that its $z$ axis lies along the surface normal, is that right?
Jul
26
comment Law of Clavius explained
There are two possibilities: Either $P$, or $\lnot P$. But by the premise, if $\lnot P$, then $P$. So in either case, $P$.