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visits member for 4 years
seen May 22 at 1:36

Aug
6
awarded  Yearling
Nov
16
comment Time in Mathematics
Homotopy theory is really all over the place, I probably couldn't give a better reference than Hatcher's Algebraic Topology. For Lie theory, I would suggest John Stillwell's Naive Lie Theory. It only requires linear algebra and calculus and focuses on examples.
Aug
6
awarded  Yearling
Apr
16
comment Nice examples of groups which are not obviously groups
The easy way to see that this is a group (and the reason you got downvoted I expect) is that this is easily seen to be a group of matrices because the action of PSL(2,C) matrices on the extended complex plane by möbius transformations is actually just the action of PSL(2,C) on CP^1 by linear transformations, and that is easily seen to be a group if you know the properties of matrix multiplication.
Oct
2
accepted $\mu$ on $\mathcal{A}$ is $\sigma$ finite if and only if $\mu$ on $R$ is $\sigma$ finite
Sep
29
answered $\mu$ on $\mathcal{A}$ is $\sigma$ finite if and only if $\mu$ on $R$ is $\sigma$ finite
Sep
23
comment $\mu$ on $\mathcal{A}$ is $\sigma$ finite if and only if $\mu$ on $R$ is $\sigma$ finite
It is a problem in Benedetto and Czaja "Integration and Modern Analysis". I think I found a solution to the problem now, should I post it as an answer here myself?
Sep
22
asked $\mu$ on $\mathcal{A}$ is $\sigma$ finite if and only if $\mu$ on $R$ is $\sigma$ finite
Aug
6
awarded  Yearling
Mar
28
answered How can one visualize topological quotients or develop intuition for handling them?
Mar
20
comment Applications of the p-adics
Measuring the circumference of a circle by knowing its diameter, perhaps?
Mar
20
answered Matchings Containing Given Edges
Mar
8
comment looking for an imbedding of the Torus in 3-dimensional euclidean space
Be careful with this. If you choose the parameters $R=r=1$, then your torus will not have a real hole in the middle (see the "horn torus" picture). Look on the wikipedia page, it says that $R$ is the distance between the center of the "hole" and the center of the "tube" around it, and $r$ is the radius of the tube. If $r \geq R$ then you won't get a real hole, better to choose values like $R=2$ and $r=1$. These radii do not need to be both $1$ since stretching the torus does not change its topology.
Mar
8
comment Iterate the points around the edge of a rectangle
How are you given the data of the "rectangle"? The coordinates of its four corners? A list of the lattice point it intersects? the coordinates of two opposite corners?
Mar
8
answered looking for an imbedding of the Torus in 3-dimensional euclidean space
Feb
6
answered what is Prime Gaps relationship with number 6?
Jan
26
answered Does any rotation matrix in 3-d space have only one non-zero eigenvector?
Jan
25
awarded  Benefactor
Jan
24
comment How to show that the image of a certain projective embedding is an algebraic curve?
Thank you very much! I am interested in the "elementary argument". For example, for $n=3$ I can see that $f_1, f_2, f_3$ must respectively have a pole of order $0$, $2$ and $3$ at $o$ and so there must be an equation of the type $c_1 f_2^3 - c_2 f_3^2 - c_3 f_2 f_3 - c_4 f_2^2 = c_5 f_1 + c_6 f_2 + c_7 f_3$, because you can choose the coefficients on the left hand side to make the pole at $o$ of the left hand side of order $3$ or less and therefore the function is a linear combination of $f_1,f_2,f_3$. Doing similar things for higher $n$, when do you know when you have enough equations?
Jan
23
accepted How to show that the image of a certain projective embedding is an algebraic curve?