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6:00 PM
No. $C^0(G, A) = A$.
 
@BalarkaSen someone in the forums also said what you said, and I left them a comment about it
$C^0(G, A) \approx A$
by identification
But it equals functions from $\{1\}$ into $A$
 
Yes, functions from a singleton to $A$ is in natural bijection with elements of $A$.
 
Yes, so it's not equals there, that's notation abuse!
:D
 
It's objectively a better notation that what you were saying, because you, unlike me, were wrong!
 
Or I'm not sure yet, maybe it should be $A$
But how do you get $ga$ and not zero there?
$f() = f(g_0) = const = a$ you're saying?
So there's no arguments to $f$
 
6:03 PM
The first term in the differential is literally $g_0$ acting on the value of $f$. In this case it's $g_0 \cdot a$.
$f(g_0)$ is nonsense
 
I think this confusion is mainly a problem of extending the formula to $i=0$, where the expression isn't very clear
 
$G^0 = \{\star\}$ by convention. It's a singleton.
 
Therefore $g_0 = \star$
I'll try both ways and see which one causes $d^{i+1} \circ d^i = 0$ map
 
No, $g_i$'s are used as elements of $G$, arguments of $df$ for $f \in C^n(G, A)$.
 
I see
Now it makes more sense
 
6:06 PM
@s.harp It's immediately clear by trying to understand what $H^0$ means. $H^0(G, A) = \ker d_0 = A^G$ is the subgroup of $G$-invariants of $A$.
 
whoooosh a spaceship just flew over my hut
 
The symbol-manipulation doesn't help, one should learn to understand the meaning behind that massive formula of $d$
 
The higher terms are measures of how close the previous term was to being exact
 
Spoken like a true algebraist
 
6:09 PM
Still don't get it... goes back to studying
 
Haven't done much algebra lately
A slight bit of probability theory, but only some basic stuff as part of an online course on AI
 
That's pretty cool
Why are you taking a course on AI
 
Out of curiosity
 
Hah
 
I do hope to be able to make an AI that can play mahjong at some point. But I should probably start by making something that can play it first.
 
6:12 PM
Lmao that'd be amazing
 
Mainly because the ones I find in various software tend to be terrible and way too easy to beat
 
I learnt this thing called the VC dimension that's apparently both a very useful probabilistic methods tool and is used in machine learning
 
interesting
 
@BalarkaSen so $ga - a$ kind of measures how far off $ga$ is from $a$?
In the group ring?
 
Yes
Not in the group ring
Literally in $A$
 
6:18 PM
Yes, I see now
because $G$ acts on $A$
I should re-read the first part of the book it's only a few pages in so far
Read it 2 weeks ago
@BalarkaSen what langauge would you use to code the AI thing?
I mean at @TobiasKildetoft
 
Not sure
 
If you want a nice gui to go with, I do PyQt5 and am learning QtQuick in C++ (Qt Creator IDE)
 
No idea yet what is suitable for the actual AI part. The rest would probably be in something like c# since that is what I know the best
 
Python is very nice for GUI stuff and has AI libraries for it, such as Orange
 
Possibly using Xamarin and making it fully cross-platform
 
6:21 PM
With orange you can actually do some AI tests visually (that's what orange is)
Oh nice
C#?
 
Haven't looked into Xamarin that much yet, but as far as I recall it is mainly C#
probably with some javascript for certain things (as usually happens)
 
I hate JS, I hope I don't need it for my projects
Qt Quick is mostly QML
and C++, or I'll try to keep my stuff that way
That's why web sites are usually more difficult than system programming
 
I need to do a mixture, though fortunately the front-end stuff is not the place we need to do anything most of the time
 
Though some new regulations on public websites requiring them to be accessible to people of all handicaps will change that unless we can get some specialized UI people to do it for us
I do dread if we need to look closed into the front end though
Seeing as the back-end stuff is in some places a bit of a mess, so there is the possibility that the front-end will be as well
And there are only so many times we can tell the customer that something will take many times the usual amount of time due to the poor quality of the system we have taken over
 
6:39 PM
Right
How many files of C# code is it?
 
files? Not sure actually. There are something like 20 projects in the main solution
And each of those projects probably has somewhere between 10 and 200 classes
except the main context one (this is Dynamics CRM solution), which has a ton of auto-generated classes from the database
So probably as many as 500 total including all the option sets and stuff
(the context that is)
I can't check right now, since I am on my personal computer rather than my work one
 
7:12 PM
Hi, anyone know if it's allowed to request problems for some competition (that's has already passed)?
 
7:40 PM
Is there a meaning in italian to saying something like "pro NAME, QUESTION", where NAME and QUESTION are to be replaced by a name and a question
I ask because i occasionally see people write comments to answers they recieve in this format
 
8:09 PM
It doesn't come from Italian as far as I know
 
@s.harp: I was going to say it's from Latin, although the context isn't quite right. But I looked at the link you gave. The OP is abbreviating Professor, I'm pretty sure.
Hi, demonic @Alessandro.
 
8:27 PM
@TedShifrin ohhh, my secondary interpretation was that people were basically using pro as the slang for professional or "really-good-at-this-thing guy", which also made sense and made these conversations seem rather endearing
 
Hi @Ted
Did you see I pinged you yesterday or the day before?
 
8:54 PM
Man, the field axioms can be funny: It takes no less than 13 steps to prove that -a = (-1) a
 
9:18 PM
@AlessandroCodenotti About Cayley-Hamilton?
@LegionMammal978 I don't think it should be that many steps. How many to show first that $0a = 0$?
 
9:30 PM
what kind of things can i say about the level sets of a differentiable function $\Bbb R^n\to\Bbb R$? we may have $df=0$ at certain points in the set
 
@TedShifrin yes
 
im guessing that if it is not empty ore comprised of isolated points then it (at least) admits a smooth regular path $(-\epsilon, \epsilon)\to f^{-1}(\{0\})$, ie we dont have osmething like not locally path-connected
 
9:46 PM
Suppose $aba^{-1}b^{-1}=c$, and $c$ commutes with $a$ and $b$. What's $a^{100}b^{100}a^{-100}b^{-100}$?
I believe the answer is $c^{10{,}000}$
 
$a^{100}b=a^{99}bac = ... = bc^{100} a^{100}$ , then do it 100 times more
so yep $c^{10000}$
 
10:07 PM
@s.harp Any closed subset of $\Bbb R^n$ is level set of a differentiable function.
You just have to smoothen out the distance function well enough. I can draw a picture of a smooth function $\Bbb R \to \Bbb R$ whose zero locus is the Cantor set.
 
I feel like I am living in that parable with the poisoned well asking questions on this SE
0
Q: How is a set of functions with a domain over the said set formally defined?

Victor SThis came up studying fully connected networks like Hopfield networks. Suppose something like below for a function space S: $$F \subseteq S, \ \forall{f} {\ \epsilon \ } F: f(F) \rightarrow f', f' {\ \epsilon \ } F', F' \subseteq S.$$ What does the formal nomenclature look like for such a set...

I am trying to see if there is a name for a function space where all its elements have a domain over it
Why would that be put on hold with no comments? Am I insane for asking something so ridiculous? Is everyone else insane?
In my ideal world I would either expect something like "I believe what you are describing is called a Thingamajig space" so that I can reference it
Or "Never seen something like that defined" so that I can decide if it is worth extra effort to make it defined
I will even take a "See a shrink Victor you're asking weird questions"
Anything
 
10:25 PM
@BalarkaSen In fact, of a smooth function.
 
10:39 PM
@TedShifrin hi ted, how are you?
If you could, may you please look at the following post, please?
0
Q: Limit question multivariable analysis

topologicalmagicianLet f be a map from $\mathbb{R}^2$ to $\mathbb{R}^2$ be defined as $f(x,y)=(x^2,y^2)$ let T from $\mathbb{R}^2$ to $\mathbb{R}^2$ be the map $T(x,y)=(2x,4y)$ then to show that f is differentiable at $(1,2)$ with derivative T, the following change of variables is made: $$\lim_{(x,y) \rightarrow...

I really love how you explain things, so I'd be very glad if you could explain this to me, please
I understand it at an intuitive level. I'm trying to formalize my understanding
Or anyone for that matter, if anyone could help. I'd be so glad
 
@TedShifrin 6 steps for $0a=0$ is the shortest I could come up with: $0a=0a+0=0a+(0a-0a)=(0a+0a)-0a=(0+0)a-0a=0a-0a=0$
It takes 7 more steps for the entire statement: $-a=0-a=0a-a=(-1+1)a-a=((-1)a+1a)-a=((-1)a+a)-a=(-1)a+(a-a)=(-1)a+0=(-1)a$
 
11:17 PM
@LegionMammal978: Way too hard. Consider $0a=(0+0)a$.
@topologicalmagician The point is that you can always set $x=a+h$ (whether with real numbers or with vectors), so letting $x\to a$ is equivalent to letting $h\to 0$. If you look at my YouTube lectures, you'll see that I always use $h\to 0$ for this because it saves algebra/steps.
(Since you seem to be lacking confidence, note that the definition of $x\to a$ is that $\|x-a\|\to 0$ (here I'm assuming vectors). But by definition $x-a = h$, so $\|h\|\to 0$, which means $h\to 0$. And all vice versa. OK?)
 
11:37 PM
@TedShifrin I'm not exactly sure how it can be simplified further, using strictly the axioms. To cancel out the original $0a$, we need to introduce a $-0a$, and then we use $0a+0a=(0+0)a=0a$ to remove the additional $0a$ we introduced, which ultimately takes 6 steps.
I suppose $-0a$ in particular isn't necessary, but I fail to see how it would make the chain any shorter.
 
11:59 PM
@LegionMammal978: Did you try doing what I said? I take three more steps from where I am. $0a=(0+0)a = 0a + 0a$. Now add $-0a$ to both sides, and I'm done.
 
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