Brian Rushton
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Registered User
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I support research for Congenital Muscular Dystrophy (see curecmd.org).
List of "math" movies: Math that should be a movie: The Fredholm Alternative, Smooth Operator. |
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May 4 |
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Why is it hard to prove that the Euler Mascheroni constant is irrational? Does this mean the Oiled-Macaroni constant is a renormalized feta function? Mmm... Greek food... |
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May 4 |
asked | Discrete Morse theory and chess |
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Apr 29 |
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Why isn’t $\langle x,y,z|xyzx^{-1}y^{-1}z^{-1}\rangle$ a hyperbolic surface group? Great answer, and thanks for the comments from everyone! My embedding of $G$ was a typo, which I've corrected above. It seems like any such group with an odd number of generators in the same pattern will be a surface with a point identified, right? |
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Apr 29 |
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Why isn’t $\langle x,y,z|xyzx^{-1}y^{-1}z^{-1}\rangle$ a hyperbolic surface group? typo |
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Apr 28 |
asked | Why isn’t $\langle x,y,z|xyzx^{-1}y^{-1}z^{-1}\rangle$ a hyperbolic surface group? |
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Apr 25 |
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Do quasi convex hyperbolic subgroups remain quasi convex after adding redundant generators? Great answer! I am indeed assuming number one. Your example answers the question. It seems to me that quasiconvexity will only be preserved if the subgroup is already generated by diagonal elements. Thanks for the care and time you took in your response! I had never heard of many of these equivalent conditions. |
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Apr 24 |
revised |
Do quasi convex hyperbolic subgroups remain quasi convex after adding redundant generators? Added example |
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Apr 24 |
asked | Do quasi convex hyperbolic subgroups remain quasi convex after adding redundant generators? |
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Apr 19 |
awarded | ● Nice Question |
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Apr 19 |
asked | Great mathematics books by pre-modern authors |
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Apr 19 |
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Untwisting Heegaard diagrams @Scott Taylor: That paper is very interesting; thanks! I am really just interested in knowing more about combinatorial properties of Heegaard diagrams, so that paper is great. |
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Apr 17 |
asked | Untwisting Heegaard diagrams |
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Apr 2 |
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Would a closed universe with special relativity violate causality? Does the universe have to be simply connected? Thanks you, this answers my question completely (especially the linked article!). |
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Apr 2 |
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Would a closed universe with special relativity violate causality? Does the universe have to be simply connected? Clarification |
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Apr 2 |
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Would a closed universe with special relativity violate causality? Does the universe have to be simply connected? Added small change about Lorenz group |
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Apr 2 |
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Would a closed universe with special relativity violate causality? Does the universe have to be simply connected? Reformulating mathematically |
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Apr 2 |
asked | Would a closed universe with special relativity violate causality? Does the universe have to be simply connected? |
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Mar 28 |
answered | How large is this “algebra” of defining graphs for Right-angled Artin groups? |
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Mar 15 |
awarded | ● Nice Question |
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Mar 15 |
asked | How does hyperbolicity of space time affect our lives? |
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Mar 14 |
awarded | ● Good Question |
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Mar 14 |
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Covering maps in real life that can be demonstrated to students Removed unnecessary tag and edited typos |
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Mar 13 |
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How large is this “algebra” of defining graphs for Right-angled Artin groups? Clarification |
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Mar 13 |
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How large is this “algebra” of defining graphs for Right-angled Artin groups? Thanks, Benjamin; I found this article almost immediately after reading your comment: arxiv.org/pdf/0909.4719v1.pdf. It's a good starting point! |
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Mar 13 |
asked | How large is this “algebra” of defining graphs for Right-angled Artin groups? |
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Mar 13 |
revised |
Topology, the board game Added link |
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Mar 13 |
asked | Topology, the board game |
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Dec 31 |
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The human body’s random number generator Explained reasons for not selecting a specific answer |
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Dec 30 |
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Proofs that inspire and teach It's the second edition, very last chapter (or second to last). He shows that every covering space of a graph is a graph, and that all graphs have free groups as a fundamental group. I never went through it in class, and it is really short, but I read it this summer and liked it. |
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Dec 29 |
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trigonometric non-identity What happens if you scale the numbers between 30 and 42, or some ther set? Do a and b change significantly? |
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Dec 29 |
answered | Proofs that inspire and teach |
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Dec 28 |
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Relating the angle between two vectors to max and min eigenvalues Although, I think we are applying the inverse of the matrix, so as we apply the matrix to the vector in (6) that is close to the bigger eigenvector, it gets shrunk in that direction and stretched in the other, making it twist a lot and apparently maximizing the angle. |
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Dec 28 |
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Relating the angle between two vectors to max and min eigenvalues Equation 6 says that the vector whichs gets twisted the most is a weighted sum of the eigenvectors corresponding to the biggest eigenvalue and to the smallest. So, I was incorrect above; the vector that is 45 degrees between the two is not best; instead, you use a weighted sum (eq. 6) that is a little closer to the bigger eigenvector. |
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Dec 26 |
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Relating the angle between two vectors to max and min eigenvalues Expanded |
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Dec 26 |
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Relating the angle between two vectors to max and min eigenvalues Changed problem explanation. |
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Dec 26 |
answered | Relating the angle between two vectors to max and min eigenvalues |
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Dec 23 |
awarded | ● Good Question |
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Dec 23 |
awarded | ● Mortarboard |
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Dec 22 |
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The human body’s random number generator I have to confess, after I wrote my previous comment, I realized that I accidentally voted to close while checking the previous vote to close. I didn't have enough reputation for this before. Sorry for my mess-up! |
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Dec 22 |
awarded | ● Nice Question |
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Dec 22 |
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The human body’s random number generator I agree with those voting to close that this may not be the most appropriate forum for this question. Can anyone a suggest a better place to ask this? |
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Dec 22 |
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The human body’s random number generator Made title more enticing. |
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Dec 22 |
asked | The human body’s random number generator |
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Dec 22 |
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Intuitive pictures in characteristic p I came to it myself, but I think it's based on the Red Book of Varieties' picture of $\mathbb{Z}$[x]. |
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Dec 22 |
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Intuitive pictures in characteristic p Added link. |
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Dec 22 |
answered | Intuitive pictures in characteristic p |
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Dec 18 |
awarded | ● Enthusiast |
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Dec 17 |
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Useless math that became useful What about math that was once useful but now useless? Like all of the tricks engineers had to use to multiply using slide rules... |
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Dec 11 |
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Independence using reflecting brownian motion In the second sentence, what are you showing to be 0? |
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Dec 10 |
awarded | ● Civic Duty |
