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Almost all of the questions on the front page these days are homework questions or textbook exercises. I think I'll be spending a lot less time here.

I hereby authorize whoever it may concern to post my comments as answers if they wish, whether as community wiki or otherwise if you like imaginary internet points.


2d
comment convex hull function in matlab
convhulln: "K = convhulln(X) returns the indices K of the points in X that comprise the facets of the convex hull of X. X is an m-by-n array representing m points in n-dimensional space. If the convex hull has p facets then K is p-by-n." Yep, you can definitely compute the half-spaces from that.
2d
comment if the role of a numeral system is to provide a mathematical notation for representing numbers. Then how do notation less numbers look like?
You can read more about it at The oldest set-theoretic definition of natural numbers on Wikipedia.
2d
comment if the role of a numeral system is to provide a mathematical notation for representing numbers. Then how do notation less numbers look like?
I'm not being facetious. The number five can be thought of as the property common to all sets of five objects (more precisely, natural numbers can be defined as the equivalence classes of finite sets under bijection). So a natural way to exhibit the concept "five", independent of a choice of numeral representation, is to exhibit a set of five things, as I did above.
2d
comment hand evaluate $\sqrt{e}$
The nice thing about the Taylor expansion is that (i) it converges very quickly, and (ii) you can easily derive upper and lower bounds so you know how close you are to the right answer.
2d
comment if the role of a numeral system is to provide a mathematical notation for representing numbers. Then how do notation less numbers look like?
This is a little like asking what a word looks like when it's not written down... But here's a five, for example: ❦ ❦ ❦ ❦ ❦
2d
comment draw a circle using beizer curve and co-ordinate of control points
It's not possible to draw a perfect circle with Bézier curves, but you can get pretty close. See math.stackexchange.com/q/754435/856 and spencermortensen.com/articles/bezier-circle
Apr
19
comment Zero-distortion map projection
I guess by "dendritic limit" you're imagining something like this construction of the polyconic projection? Clearly one can create an $\epsilon$-distortion map for arbitrarily small $\epsilon$ by cutting up the sphere into tiny pieces, but a map with distortion exactly $0$ feels like it should probably be forbidden by the Theorema Egregium.
Apr
19
comment Is there any statistical method to compare two curves?
Previously: Determining similarity between paths (sets of ordered coordinates)
Apr
19
comment Is there any statistical method to compare two curves?
Are these curves functions, $y = f(x)$, or general curves in the plane like spirals, ellipses, etc.?
Apr
19
comment How to teach newbie multiply of complex number
Does the other person know about distributivity of multiplication in general? What do they think about $(a + b)(c + d)$?
Apr
18
reviewed Leave Open Second derivative of $f(f(\cdots f(x)\cdots )?$
Apr
18
answered Are all polynomial-bounded functions computable?
Apr
18
comment Are all polynomial-bounded functions computable?
Is this a question or an answer?
Apr
17
revised Can you only take positive numbers into a square root?
edited tags
Apr
16
revised Is 1/113 a rational number?
added 10 characters in body; edited title
Apr
15
comment Find normal vector for the surface F(x,y)=0
A "surface" $f(x,y)=0$ in two dimensions is usually called a curve.
Apr
15
comment Why is $sinx$ the imaginary part of $e^{ix}$?
Your question is "Why is $e^{ix} = \cos x+i\sin x$?" Hans's linked question is "How to prove that $e^{it} = \cos t+i\sin t$?" I don't see how you fail to see at least a passing resemblance.
Apr
15
revised Maximizing the trace
edited title
Apr
14
comment Covariance matrix with constant diagonal
It's a multiple of a correlation matrix.
Apr
12
comment A variation of the isoperimetric problem in the plane
@Sébastien: Yes, I agree that there might be an self-intersection problem with non-convex polygons. I'm not entirely convinced by your example, but the problem probably does arise with this Pac-Man-like shape: $n$ points $A_1,\ldots,A_n$ with $A_i = \bigl(\cos(2\pi i/n), \sin(2\pi i/n)\bigr)$ for $i=1,\ldots,n-1$ and $A_n = (-1+\epsilon,0)$. Oh well. I intend to rigorously clarify the limits of my answer in the future, but I may not have time in the next three days.