Yeah we just have Crayola, also the white chalk, though it seems to not be as bad. Every now and then Hagoromo is laying around and we're all just like :O
@MatheinBoulomenos nice! Post meaning, MSE answer? Or something else?
Going pretty well. Tentatively I've decided on Galois cohomology because I'm mildly meh on doing elliptic curves with no AG, and there's probably not much of a point in doing it now if I intend to do it next year
@Daminark you might enjoy the blog post, it's mostly examples for now. The story is that a friend of mine who doesn't know rep theory but is interested asked me if I could teach it to him by writing some blog posts about it, so now I'm doing a series on that
Suppose I know that $\psi(x_u)$ can be expressed as a linear functional of some function $S(x)_u$ and I know that $S(x)=\int_0^T S(x)_u dx_u$. How can I conclude that $\int_0^T \psi(x_u) dx_u$ is also a linear functional of S(x)
@TedShifrin I wonder if I have too much examples and motivation. I start with 4 paragraphs of philosophical musings and then I give 11 examples (some of them are really families of examples) before I prove anything
This is quite good! If you are looking to get some results earlier, you could talk about how if you have a finite group, you get diagonalizability, and simultaneously if it's abelian. Probably not necessary but it's at least kinda "easy" somehow and gives a grip on things
Matt was actually talking about that today since he was starting Fourier theory of finite abelian groups (first time he explained it that I actually understood). It built up quite nicely to the idea of characters of groups
(Specifically those representations which arise out of taking the free space given by a G-set
@quallenjäger: I'm trying to sort out unfamiliar notation. It seems to me it's just that the linear functional pulls out of the integral. That's just standard.
@MatheinBoulomenos so I'm not sure in general what kind of audience you're going for, though it does seem like modulo some categorical talk and some examples, it's the kinda thing that you can understand after having taken an algebra course. If that is what you're going for, it might be good to put a disclaimer that some of the examples present (e.g. algebraic groups and parallel transport) within are meant for readers with more background and aren't necessary for reading the rest
Hello:) I have an optimization question. When the exersice says 'write the kkt conditions for the problem' means that I should write 'the kkt conditions are $\min f(x) s.t. g_i(x)\le 0, h_i(x)=0$, x feasible, $I=\{i:u_ig_i(\overline x)\}$ and there exists constants $u_i\ge0 ,v_i$ not all zero such that $\nabla f(\overline x)+\sum_{i\in I} u_i\nabla g_i(\overline x)+\sum v_i\nabla h_i(\overline x)$' am I right?
becuase if we have those conditions, we can say that $\overline x$ is minimum
Funny thing actually, combo final had a question (worth very few points but still) about naming 4 mathematicians that came up in class but whose names weren't written on the test already. In the review session, my prof stressed the importance of knowing who people are in the subject instead of just seeing some theorems
@quallenjäger the motivation behind the definition of a group-like element is the group algebra. If you consider a group $G$ (say finite), then you have the group algebra $k[G]$, the free vector space generated by the elements of $G$ together with a convolution product (that's really just taking the multiplication of $G$ on basis elements and extending it linearly.) It turns out that this thing is a (cocommutative) Hopf algebra and the comultiplication is given on basis vectors by $g \mapsto g \otimes g$
But this holds only for the basis elements, for example, for two different basis elements $g,h \in G$, we send $g+h$ to $g \otimes g + h \otimes h$ which is not the same as $(g+h) \otimes (g+h)$
I haven't given you the full Hopf algebra structure, though, we also have the counit $k[G] \to k$, that is given on basis elements by sending each $g$ to $1$ and then extended linearly
The two conditions that turn out to give exacty the basis elements we started with are $\Delta(g)=g \otimes g$ ($\Delta$ is comultiplication) and $\varepsilon(g)=1$ (this is the counit)
In mathematics, the Baker–Campbell–Hausdorff formula is the solution to the equation
Z
=
log
(
e
X
e
Y
)
{\displaystyle Z=\log {\big (}e^{X}e^{Y}{\big )}}
for possibly noncommutative X and Y in the Lie algebra of a Lie group. This formula tightly links Lie groups to Lie algebras by expressing the logarithm...
@quallenjäger I heard of BCH for p-adic Lie groups, but I haven't seen this stuff with noncommutative power series (I love it, though!) But I can't help with the details of that right now, I have to go to sleep. I don't know much about Lie theory
i'm debating placing a bounty, but the last time i did, i a. figured out the problem literally the next day, and b. got no real answers other than my own write-up.
can I ask a simple question on here about dimensional / dimensionless units?
say we had a length scale of 0 to 5 cm, and we divide this length scale by say 1/2 cm, this gives a new set of numbers that's "dimensionless". what's the difference? does dimension here mean something like in linear algebra?
and does dimensionless also mean something like in linear algebra - like, scalars?
I have little physics background, so just need to pick up some basic lingo
there is a linear algebra connection, but it only emerges once you have more than one dimension to worry about e.g. energy has dimensions of mass^1 * length^2 * time^-2
if I have several dimensional or dimensionless parameters, why is one of them referred to as the "control parameter" - I saw that in a paper today. Aren't all of them control parameters in a physical model?
I think they are fixing all other parameters but letting one vary ...
do you think I have that right?
so that if we fix all parameters but let 2 of them vary, then we have 2 "control parameters" ...
for graphs, say the interval for length is originally [0, L/3], from some paper, where L is length, using a centimeter scale. I've heard that it is typical to divide by L/3, in order to use the interval [0,1] instead. Is this called "normalization" like in math / linear algebra?
the division also throws me off, because the lengths have now all changed ...
shouldn't we be analyzing the true lengths of the rigid body?
one point is really that the analysis should be expressed in a form that doesn't care about whether you're working in units of centimeters or feet or whatever
May sound dumb, but quick question: suppose a function $\vec{v}(t)$ parameterizes a Jordan arc for all $t \in I$. Then can we express its tangent vector as a function of $\vec{v}$ alone, which is defined over $I$?
that radius of the earth will matter regardless if you work in miles or kilometers
another way to look at the [0,L/3] -> [0,1] is that you're choosing to describe the lengths in terms of proportions, e.g. a length is one sixth of L -> s=(L/6)/(L/3) = 0.5
the paper uses the term "control parameter" while a professor I talk to often talks about the paper and says "control variable" instead. Is it ok to use both terms synonymously?
Consider a smooth convex/compact domain $D\subset \mathbb{R}^n$ and a smooth, concave function $F:D\to \mathbb{R}$. Then we can define the function that simply takes the volume of the upper contour sets determined by the argument:
$$G(t) = \int_{\{x\in D \; : \; F(x) \ge t\}} d\lambda$$
where ...
another pattern: the last N-1 digits of each factoradic group appear always as the last digits in the next group
i.e. to find primes, you'd need to find the factoradics of previous primes. take the last N-1 digits and ensure that your current prime ends with those digits.
(there would be false positives, but not false negatives?)
Currently writing on the follow-up post. It's not going to be as elementary. I basically need one theorem from ring theory and then a bunch of stuff for representations of finite groups (in the case where Maschke applies, so e.g. characteristic 0) follows
One can show that it's an iff for finite groups, but I planned that for a later post where I plan to study exactly the case when the characteristic divides the order
Earlier today I talked to my professor asking about topic choice and one of his recommendations was essentially about having Galois actions as representations and trying to do some computations of that sort, the logic being that when people introduce either, they often don't include the perspective of the other in examples, so it'd be the kind of thing that's worth having on a website for people to look up
In the midst of that he said "Do you have a website? In grad school that's a thing you should have for sure"
it's about a magma algortihm. My prof has seen some regularity in certain Galois reps, but so far he could only compute very few examples, because the stuff is computionally expensive, that's why he hesitates to call it a "conjecture" so far
My boys, $k$ be field, and let $A,B$ be $k$-algebras, say finite-dimensional. Does it ever happen that the inclusion $\operatorname{Alg}_k(A,B)\hookrightarrow \operatorname{Hom}_k(A,B)$ splits?
It probably does, but what are some equivalent conditions?
Hello, I have been struggling with a question if someone could help that would be appreciated. If I have two points lets say x and y, those points are over edges of an image. I can calculate the tangent lines l_x and l_y. Now I have a homography H, and I want to compare the tangent lines l_x and line l_y so I want to know how similar are they, using the dual homography l_x' = H^{-T}l_x. and I want to compare how 'similar' are l_x' and l_y this is all in P^2, I don´t know what to do