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00:51
Hello! I'm having trouble proving that there is and isomorphism between Dedeking Cuts and Cauchy Sequences, could someone take a view to this post? math.stackexchange.com/questions/4423954/… thank you :D
01:49
Munchkin must have stolen the room.
@TedShifrin should I post my question on main ?
Sure. Just boil it down to clear essentials. No product of 4 curves unless that is central.
@TedShifrin Yeah it is central I guess, but I will see how I can strip down the details.
What you were asking me needed $C\times X$ for a variety $X$ of dim $\ge 2$.
If more is needed, figure out why.
I see
thanks I have noted that down
 
4 hours later…
05:43
15 hours ago, by Koro
I know that ax+by=ab-a-b has no positive integer solutions. This is because (b-1,-1) is a solution of the equation so all solutions of the equation are given by x= b-1+m b, y= -1-ma, where m is any integer. Clearly, x and y can’t both be positive for any m.
0
Q: The postage stamp problem from Dummit and Foote's chapter 8.1

KoroLet $a$ and $b$ be two relatively prime positive integers. Prove that $1)$ every sufficiently large positive integer $N$ can be written as a linear combination of $a$ and $b$ where $x$ and $y$ are both non-negative, i.e., there is an integer $N_0$ such that for all $N\ge N_0$, the equation $ax+by...

06:05
@Koro This is known as Sylvester's problem. Took me ages to unravel.
06:29
@Koro I had almost finished typing up an answer when the question got closed.
06:47
uhoh! something's not quite right here :-)
and a missing ℏ/2
@uhoh huh?
@copper.hat I didn't recognize the "p" in the 2nd one as momentum until after I posted it here - I thought it was going to turn out to be a mystery in need of a solution.
 
2 hours later…
08:50
is my proof reasonable or not?
@Koro Take a look at this answer.
 
1 hour later…
10:16
@copper.hat thanks a lot :). Too bad that the question got closed.
This answer math.stackexchange.com/a/66983/266435 answered my question.
 
4 hours later…
14:13
@Koro Yes, Andre's answer is understandable.
what sort of thing is the Laplace transform used for in math other than differential equations?
 
4 hours later…
dtn
dtn
17:45
$L_{1}=u_1^TJ_{1}u_1$

$L_{2}=u_2^TJ_{2}u_2$

$L_{3}=u_3^TJ_{3}u_3$

where $u_{i=1,2,3}$ - 3$\times$1 vector;

where $J_{i=1,2,3}$ - 3$\times$3 matrix;

$\boldsymbol{L}=\begin{bmatrix}L_1 & 0 & 0\\0 & L_2 & 0\\0 & 0 & L_3\end{bmatrix}$
I need to combine these operations into one to get the given matrix $\boldsymbol{L}$. I need to use either a matrix product or a tensor product. Help, I can not find the operation.
18:07
@Derivative probability, among others. while in the realm of differential equations, it is very much used in control system design & analysis.
@dtn your question is vague. combine what operations on what?
dtn
dtn
18:26
@copper.hat I have three vectors and three matrices. I need to come up with a formula that would give a matrix whose diagonal elements would be the quadratic forms I have given. At first I thought that three vectors could be augmented into a matrix. Then I can use something like the formula: $\boldsymbol{L} \approx \boldsymbol{u}^T\boldsymbol{J}\boldsymbol{u}$
But the problem turned out to be that, firstly, my J matrices are different, and secondly, there are side off-diagonal elements in the result.
I thought that tensor operations would help me, but I haven't figured them out yet.
19:15
Wow. Munchkin really has killed this room!
@dtn You can do this with a $9\times 9$ matrix with 3 blocks. You can also do this as a tensor product.
ted: my wife gets back today, so i'll be off 100% child care duty soon.
and then to fill the chat with more nonsense.
I need a sanity check: I'm comparing things in $H^2$ and $H^3$. Suppose you have a quadrilateral with all edges and angles being identical, and which you can tile $H^2$ with by packing 5 around every corner. Then you have a cuboid with all faces and dihedral angles being identical which you can tile $H^3$ with by packing 5 around every edge. Should the edge length of the quadrilateral in $H^2$ necessarily equal the edge length of the cuboid in $H^3$?
I feel like it should be, but my calculations are giving different results, which would imply that my calculations are wrong
@TedShifrin are you familiar with push forward of cycles ?
19:32
@Rithaniel That takes some thought. How are these different $H^2$ sitting in $H^3$?
context, adeek?
Well, this is meant to be two entirely different cases. Quadrilaterals in $H^2$ and cuboids in $H^3$. However, I think I might have found an assumption I was making that clarifies why they would have different edge lengths, and I'm trying to articulate it.
Given a set of five cuboids around an edge and one of the two vertices that define that edge, consider the faces that have that vertex as one of their vertices (and which lack the other vertex of that edge as one of their vertices). Those face are not coplanar? Right?
Yes, but the faces are in totally geodesic $H*2$s, I assume.
@TedShifrin I am just trying to understand let us say we have rational function over some subvariety V $g = \frac{g_1}{g_2}$ then $div(g)_V = div(g_1)_V - div(g_2)_V = V(g_1) \cap V - div(g_2) \cap V$
I want to understand exactly the push forward of those cycles
I don't recognize the $H\ast 2s$ syntax immediately
Stupid typo on ipad
19:38
let us say we have morphism $\rho : V^{\prime} \rightarrow V$ the push forward gives the divisor $div(g \circ \rho)_{V^{\prime}}$ right?
your equation with intersections is surely not correct.
why ? I am not assuming any multiplicity?
do you know that the divisors in question are transverse to $V$? How?
yeah I have that it is in the specific situation that I am looking at
This has to be a scheme-theoretic intersection in general.
19:42
yeah
can I discuss with you my general situation.
Maybe you have an idea
it is ok if you don't want too though
I truly haven’t thought about this stuff in decades.
oh okay
my supervisor is sick I have been worried about him for few weeks now
2 weeks
Oh dear. Covid?
@TedShifrin no apparently he woke up one day with seeing double vision and it turns out to be Macular degeneration
they first ruled out neurological condition like stroke I am happy about that
that's on one side of my gene pool, my mom was effectively blind for the last decade if her life.
19:47
Ah, one of my old friends has that in one of her eyes. Serious stuff.
but she’s 75.
@TedShifrin no he is young
he is 65
That's rough, Adeek. I hope he comes out of it okay
@TedShifrin it doesn't lead to blindness or anything like that?
@Rithaniel same
LOL, not young. I’ve been falling apart since my 50s and I turn 70 next year.
it can, I think.
that sucks
19:51
My mom's in the hospital right now with Pneumonia. They aren't sure exactly what caused it, but it's certainly a complication from either her cancer or the chemo treatment
hope she gets well.
Yep, same
I will think good thoughts, i had radiation, no chemo, when I had cancer, but I ended up hospitalized with anemia the week before surgery.
@Rithaniel I hope she gets well as well
I am sorry about that
Yeah, everybody has had stressful experiences with people needing to be in hospitals
19:58
Wow. For me this was almost 10 1/2 years ago.
@Rithaniel my mum had breasts cancer but thankfully she was treated
not with chemo though
but she is ok now
Yeah, my mom has it in her throat. Can't eat (or speak in anything more than a whisper) as a result.
that sucks
I’m so sorry, Rithaniel.
Ye, let's talk about math
I think I've got the solution to my hyperbolic conundrum: Given a set of five cuboids around an edge, to relate the edge lengths to the edge lengths of five quadrilaterals around a vertex in $H^2$, we need to find a projection from $H^3$ to $H^2$ where the cuboids get flattened to quadrilaterals. That should be the projection onto the plane that cuts through the midpoints of the edges of the cuboids parallel to their shared side.
However, the edge lengths of these quadrilaterals after the projection are the geodesics of closest approach between the edges of the cuboids. So, the length of the edges of the cuboids themselves should be longer, right?
(Dangit, too slow to get that last typo. Should be "shared edge," not "shared side")
20:11
Is this projection or intersection?
Hmmm, might be intersection? I don't really know how projections work in hyperbolic space, now that I think about it
Yeah, it's intersection
I have never worked it out, but you still follow geodesics orthogonal to the subspace you’re projecting to.
dtn
dtn
20:52
@TedShifrin Ted, what would the formula look like?
@TedShifrin that for this message
21:09
Honeybombs are weird in hyperbolic space. Like, in Euclidean space, you can have a cubic honeycomb, and if you take a vertex and surround it on all sides by cubes, you end up with a larger cube (edge length twice that of the smaller cubes). If you do the same with cuboids with dihedral angle $\frac{2\pi}{5}$ in hyperbolic space, you end up with twenty cubes around a vertex, and the space they fill up is a 60-sided polyhedron with none of the faces being coplanar
Now, this polyhedron with 60 quadrilateral faces. It, too, can form a honeycomb of hyperbolic space. I can't even begin to imagine what that would look like, though
@Rithaniel honeybombs = sticky munitiions?
lol, yes. Either that or a thing that you stir into your food to make it super sweet
Even after you pointed out the typo, it took me a minute to find it
21:29
@TedShifrin I have figured out a nice problem
I did a a lot of computations though
I think I need to rewrite things multiple times
to make sure I don't catch any errors

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