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visits member for 3 years, 8 months
seen Jul 23 at 10:21

Jul
18
comment Canonical term for $\overline X / X$ where $X$ is a normed space.
This appears in the theory of Hilbert complexes, as quotient of the closure of the boundaries by the boundaries. More, generally, for Banach complexes see: link.springer.com/article/10.1007%2FBF02922133?LI=true
Sep
9
comment Formula for surface measure of spherical cap on $S^n$.
In the section 'hyperspherical cap', the wikipedia article gives a formula for the surface in terms of regularized incomplete beta functions. I wonder whether a single integral formula like for the volume, at the beginning of the same section, does exist.
Sep
8
comment Formula for surface measure of spherical cap on $S^n$.
I am specifically looking for formulas nicer than there.
Apr
5
comment Boundedness of a Solution Operator
@user17904: You need to show that for Sobolev space $H$ of sufficient regularity the trace from $H$ to $L^2(\partial\Omega)$ has closed range. Than a bounded right-inverse exists by functional analysis. Typically, you can prove surjectivity, say, by partition of unity, smoothing and an explicit construction.
Mar
7
comment pseudoinverse under change of norm
I have completely rewritten the question.
Mar
4
comment An variation of “Lk” in simplicial complexes
@StefanH.: Yes, thanks.
Feb
13
comment How can not-equals be expressed as an inequality for a linear programming model
It is intutive it does not work, because polyhedrons are convex and closed, while not-equals correspond to non-convex open regions.
Jan
29
comment Approaches to integrate $\int_0^1 \frac{x}{\sqrt{a+bx+cx^2}} dx$
Thanks, that got me on the right track.
Jan
27
comment If A $\subset S^n$ has spherical diameter < $\pi$, then $S^n - A$ contains a closed semisphere.
The original statement was blatantly wrong. I have editted the question into what I actually meant.
Dec
19
comment Distinction between 'adjoint' and 'formal adjoint'
These lines on Wikipedia only describe the construction for a differential operator. I have been concerned about general operators and their formal adjoints.
Nov
2
comment Solid angle between vectors in n-dimensional space
Your second formula is quite awkward, because you apply arctan against a vector.
Jul
18
comment Proof by Induction $n^2+n$ is even
You know you don't need induction, do you?
Jul
11
comment Minimizer of $p$-average of distances to points $x_1,\dots,x_n$
@ChristianBlatter: A name, like some exotic mean, would be helpful, of course.
Jul
11
comment Minimizer of $p$-average of distances to points $x_1,\dots,x_n$
@Paul: Yes, by definition. The vector $D$ is just a formal device.
Apr
7
comment Antisymmetric functions in higher dimensions
Okay, maybe a nice definition of signed permuation of coordinates is a permuation matrix times a ${-1,1}$-diagonal matrix, and the signum is the determinant of that transform.
Apr
7
comment Antisymmetric functions in higher dimensions
That's interesting. Your functions are smooth, are they? And could you please define what a signed permuation and its signum mean?
Mar
18
comment How should I understand “$A$ unless $B$”?
That post is nicely written. Thanks!
Mar
13
comment Derivative in complex analysis
@anon: I am curious and my complex analysis is rusty, too. Why is $f$ constant?
Mar
7
comment Which formula do I use to integrate $ \int {\sqrt{x^2 + 81} \over 2} \,dx $
In your final expression, the variable $x$ appears outside the integral, without any proper definition there. You should change this notation.
Mar
1
comment First-order derivatives in differential forms calculus
Because that is the way the Lie differential is defined.