123,711 reputation
8117240
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 49
visits member for 2 years, 3 months
seen 1 hour ago

I did study math and had a knack for it, but I am sooo out of that business now ...


56m
comment Using probability to detect exam cheating (identical wrong answers)
If all students wrongly answer that the Earth is flat, it may not be a case of cheating but of bad teaching ...
4h
comment Is $z/\sin z$ analytic in the complex plane?
What is $f(\pi)$?
15h
awarded  notation
1d
answered What ring-sum of vector spaces can possibly mean?
1d
answered Why don't graphing tools represent holes in a graph?
1d
comment Why is boundedness necessary in this proof that addition and scalar multiplication are continuous maps in the metric space induced by a norm?
Just write down the triangle inequality as used to estimate the left hand side
1d
comment What motiveted Gauss to formulate his theorem on quadratic reprocity?
Are you trying to learn this directly from the Disquisitiones?
Dec
18
comment Construct quadrangle with given angles and perpendicular diagonals
@Narasimham Yes, the solution is unique up to similarity, though this is not immediate from the IVT proof (but the transformation described changes the angles at $P$ monotonically)
Dec
18
comment Construct quadrangle with given angles and perpendicular diagonals
A very interesting twist on the problem statement!
Dec
18
comment What's the definition of a “local property”?
I suggest to dig especially into the differences between connected, locally connected, semilocally connected. Which if these is local?
Dec
18
comment How is a part of eulerian path called?
Not every path that visits an edge at most once is necessarily a part of an Eulerian path
Dec
18
comment $G$ is an open subset of $ \mathbb R$ such that $ 0 \notin G $ $ \implies$ {$xy | x , y \in G$ } is open?
@Nishant Therer is none. It's really just the fact that the union of open sets is open, and - if one does not like the word homeomorphism - division by $y\ne0$ is continuous, hence $Gy$, being the inverse image of the open set $G$ under a continuous map, is open.
Dec
17
comment Prove there exist an isomorphism
I assume $V$ is a vector space over some field $k$ and $U$ is ...?
Dec
17
comment Define a bijection function
or $9$, depending on your $\mathbb N$.
Dec
17
answered Recursion. I don't understand proof.
Dec
17
awarded  Caucus
Dec
17
reviewed Close Extensions on matrix factorization
Dec
17
reviewed Close How to select the right books?
Dec
17
reviewed Close How to do sampling for the following problem.
Dec
17
reviewed Close What kind of an optimisation problem am I dealing with?