127,823 reputation
9121249
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 49
visits member for 2 years, 4 months
seen 8 hours ago

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


Jan
20
revised Do minimum polynomials always have a nonzero discriminant?
added 175 characters in body
Jan
20
answered Do minimum polynomials always have a nonzero discriminant?
Jan
20
answered Sequence of positive reals
Jan
20
comment Prove a convergent sequence has either a minimum, a maximum or both.
@idm The first three lines do not prove everything. If we let $a_n=\sin n$ then we don't have convergence, but we still have all from sentene two on, i.e., for $\epsilon=1$ we have $|a_n-0|<1$ for all $n$. (And of course $a_n=\sin a_n$ has no max/min)
Jan
19
answered A finite group of isometries is isomorphic to a subgroup of $SO(3)$?
Jan
19
answered Prove that a graph with the same number of edges and vertices contains one cycle
Jan
19
comment Can you be 1/12th Cherokee?
@bof Yeah, that is all somewhat convoluted and as I said part of the underlying assumptions. Sufficiently many generations ago, there was just some slime in the Ocean ... If we go ahead (and perhaps also drop the idea of race) and simply speak about alleles leading to some phenotype, then these are probably not even distributed over all 23 pairs of chromosomes. Then (ignoring mutations) one can have only a certain fraction, always a multiple of some fixed $\frac1N$ with $N<46$, of the corresponding allels. Problem number one is to explain, which of these make "Cherokee-ness".
Jan
19
answered The intersection of a and b is a superset of the product when a and b are ideals
Jan
19
comment The intersection of a and b is a superset of the product when a and b are ideals
You correctly writ $\supseteq$, but wrongly speak of subset.
Jan
19
answered A particle which travels a unit distance in a unit time, and starts and ends with velocity 0, has at some time an acceleration $\ge 4$.
Jan
18
awarded  Good Answer
Jan
18
awarded  Nice Answer
Jan
18
answered Can you be 1/12th Cherokee?
Jan
18
answered Is this function/series periodic?
Jan
18
comment Give three examples of complex numbers where z = -z
... or maybe $z=-\bar z$?
Jan
18
answered Is $x = 2014$ is the solution of inequality $|z_3-z_1|^x$+$|z_3-z_2|^x \le |z_1-z_2|^x$?
Jan
18
comment prove this theorem $\vdash (\exists x_i (A\to B)\to (A\to \exists x_i B))$
Informally, pick $x_i$ such thhat $A\to B$. Then using $A$ we conclude $B$. Hence for this $x_i$, we have $B$.
Jan
18
comment Topologies induced by functions
Alright, then letting $a=1, b=0$, we see that the domain topology must be at least as fine as $U$ ...
Jan
18
comment Topologies induced by functions
Wouldn't any function $f\colon \mathbb R\to (\mathbb R,U)$ be continuous if $U$ is the indiscrete topology? - Or wait, do you mean to vary the topology on the domain but keep the standard topology on the codomain?
Jan
18
comment Is there a standard way to obtain an approximation piecewise-linear function for a function
It's no good idea to call your approximating function $f'$ because you will certainly need to use the derivative $f'$ of $f$ t estimate the error :)