167 reputation
17
bio website math.leidenuniv.nl/~jcommeli
location
age
visits member for 2 years, 9 months
seen yesterday

2d
answered Solving Fulton and Harris exercise 2.4
2d
comment Solving Fulton and Harris exercise 2.4
Please provide the exercise number from Fulton–Harris.
Jan
23
answered group homomorphisms from the real line to infinite torsion abelian groups
Jan
23
comment group homomorphisms from the real line to infinite torsion abelian groups
@user66257 — The group $\mathbb{R}$ is a $\mathbb{Q}$-vector space. (Maybe this helps to see why Eric Wofsey's comment is relevant.)
Jan
23
comment group homomorphisms from the real line to infinite torsion abelian groups
Off-topic: why is there exactly one mathematical symbol in your question that deserves MathJaXification, while all the others have to be satisfied with plain cold sans-serif typesetting?
Dec
20
awarded  Constituent
Dec
19
revised If $G/Z(G)$ is finite, then $|G'| < \infty$
Improves formatting
Dec
19
suggested approved edit on If $G/Z(G)$ is finite, then $|G'| < \infty$
Dec
15
awarded  Caucus
Dec
15
comment Maths to take a user chosen number to a predictable number
See en.wikipedia.org/wiki/Collatz_conjecture. Ask them to run the computations until they stabilise. Definitely works for integers $\le 100$, and conjecturely for arbitrary positive integers. (Oops, I just remembered that it always ends in $\ldots,4,2,1,4,2,1,\ldots$; so maybe this is not a very good idea.
Dec
15
awarded  Critic
Dec
15
comment $a_1^3+a_2^3+…+a_n^3=0 \Rightarrow a_1+a_2+…+a_n=0$ it is true or not?
Please reconsider whether this should be tagged abstract-algebra. The tag description says: “Abstract algebra is the study of algebraic objects. Some of the more common algebraic objects are groups, rings, fields, vector spaces, modules, and other advanced topics.”
Sep
30
awarded  Explainer
Jun
16
comment Irreducibility of $x^n-x-1$ over $\mathbb Q$
@Corvus — To echo TedShifrin, the polynomial ring $\mathbb{F}_{p}[X]$ is infinite, the set $\mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is finite. Hence the natural map $\mathbb{F}_{p}[X] \to \mathrm{Map}(\mathbb{F}_{p}, \mathbb{F}_{p})$ is not injective. To stress the difference, let me ‘prove’ that $\mathbb{F}_{2}$ is algebraically closed: Take a non-constant polynomial $f$, then $f$ is not constant $1$, and as $\mathbb{F}_{2}$ has only two elements, $f(x) = 0$ for some $x \in \mathbb{F}_{2}$. Thus $f$ has a zero, hence $\mathbb{F}_{2}$ is algebraically closed. $\square$ Spot the error.
Jun
3
comment When do we have that Absolute hodge classes= Hodge classes for complex projective manifolds?
I think, if the Lefschetz operators are algebraic, then André's motivated cycles are algebraic.
May
27
comment A simpler expression that is always smaller or larger
Well, write your function as $an^2 + bn + c$, where $a,b,c$ are fractions. Then it is already pretty simple. Next, you can consider if you want your estimate on a particular domain, or on all of $\mathbb{R}$. Depending on the answer, you might be able to round $a$ to an integer, and get rid of $b$ and $c$.
May
27
answered A simpler expression that is always smaller or larger
May
27
answered Why do the addition of linear equations all pass through the same point
May
27
suggested rejected edit on can someone give me the solution with the proof?
May
27
comment Dimensions of eigenspaces.
Figure out what it means to be in either of the eigenspaces: How are matrices $A$ called that satisfy $A = A^{\perp}$, and what if $A = -A^{\perp}$? It shouldn't be too hard to figure out a basis/the dimension for the eigenspaces, once you have done that.