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00:00
Then there's your answer. $f(x)$ is a scalar, so there's no difference between the 2-norm and the absolute value of the difference.
sorry, $f:R^m\to R^n$
Ah.
Then I have no idea.
What's a good way to say "$y$ such that $y \not \in \{x, \overline x\}$"?
$y\neq x,\overline{x}$?
$\overline{x}$ is?
00:03
The complement of $x$
Complement?
$\overline x = \text{not } x$
I'm specifically talking about in terms of events.
@Semiclassical Well, I was hoping for a way to say something along the lines of "$x$ and $y$ are distinct and noncomplementary."
Is there a better way to say that?
Hmm.
Don't know.
And is the way I just wrote it correct?
I think "some event $y\neq x,\overline{x}$" works for what you wrote above.
00:05
I want to say something along the lines of $P(x | y) = 1$ for all $y$ distinct from and noncomplementary to $x$.
$P(x|y)=1$ unless $y=x$ or $y=\overline{x}$.
To describe events which are globally independent of all other events.
Alright, I guess there really is no better way to say it.
@PVAL This isn't responding particularly well to me, do you have a hint?
@Daminark Let $H$ be a codim 1 subspace of your ambient space. Find a function f_H: M \to R which singular points p of f_H correspond to points with T_pM=H.
00:24
Alright, thanks @PVAL! I'll think about that
00:35
@Dami do you have any cool infinite dimension vector space problems?
01:04
Huh, triangular matrices are a thing
Yeah.
Well, fuck. I have two hours to write a five page essay
I think I've figured sometihng out in math, but I'm not sure if anybody else has seen this pattern before or thought of this before. How can I find more information on what I'm working on?
It's to do with sums of numbers, such as 1-10.
@MewoMix On what
@Balarka Assisted Suicide.
Eek
They give stuff like that as essay topics?
01:07
That's a pretty average essay topic.
Pick something controversial and ask students to take a side and argue for it.
Hopefully, it's an ethical or moral discussion, rather than an essay about the practical aspects.
@SimplyBeautifulArt In regards to triangular matrices, you're talking about square matrices which have entirely zeros either below or above the diagonal, right?
Well, honestly that comment is slightly not politically correct.
@Anheuser I think that's the triangular numbers. Different
@axoren that'd be like if we were talking about an essay on abortion or religion and you said "I hope it's not an essay about the practical aspects."
I mean, these are controversial topics and people will take one side or the other.
So, generally speaking, assisted suicide could be said to have practical aspects.
Yeah they will. That's why they are strange choice of topics for high school essays.
01:11
@Anheuser I meant in terms of assisted suicide procedures, specifically the practical aspects.
Oh, he's a high school student! I see.
Because that would be a very uncomfortable essay to write, spending a lot of time talking about people dying in a variety of ways.
I remember writing essays on hamlet....nothing else.
I'm a middle school student
@Axoren I think students look for something to argue for/against
@MeowMix holy moly !
@MeowMix when I was in middle school I was reading fiction books and playing Fable.
01:13
@Anheuser Now that he says he's in middle school, it's more clear now that he's in that age-group where they ask for that argue for/against style of work.
Those were the worst.
Because you generally need to pick a side on a topic you don't feel strongly about at all.
hey
I have nothing to argue for or against.
Or you are forced to take the side you're actually opposed to.
@Axoren I honestly cannot relate, my middle school days are slightly hazy and the memories I do have paint a bleak picture of the educational system I was in at the time.
I had to write a thesis about Corn in my Freshman year of college. I can say that regardless of what Middle School is like, if you end up taking the wrong seminars, you're in for a snorefest.
01:15
@axoren a student should be made to argue a point he does not relate with, to teach them better debate skills.
@axoren !!!! hahahahah!!!!!!!!!
The Honors program is a joke, stay out of it. Anything that looks like a pseudo-honors program is also a joke, avoid it, too.
why should someone be taught debate skills
I also hate being held behind, because nobody will let me skip the superfluous years of math and take electives instead, ones that interest me
Because then they could convince you why someone should be taught debate skills.
HAAHaHAH!
Well done @axoren , well done!
01:17
@Axoren why do they need to convince you why someone should be taught debate skills
@MeowMix Enjoy your punitive years, young sir.
@BalarkaSen Because it could end this line of questioning very quickly :P
But generally, being able to debate allows you to resolve subjective biases by defending them against another person and losing, or strengthen beliefs and conjectures by being able to successfully defend them.
@MeowMix I've never heard of a middle schooler knowing what algebraic geometry was. Take these years in stride and develop your mathematical ability.
@axoren that is well said.
@Anheuser Sometimes, I find middle schoolers knowing algebra and geometry independently.
@axoren Yes, this is more commonly the case!
01:19
I'm studying under the guidance of the Ted Shifrin
Interesting. I take it he's why you're here in this chatroom as opposed to reddit as most students your age would be?
@MeowMix Wow, congratulations! That is very impressive. You are like a young Terrance Tao!
@Axoren I just think if someone feels the need to resolve certain subjective biases or strengthen beliefs about certain things, they will automatically develop a line of reasoning in their defense. Making someone "practice" this by debating about topics he or she feels ambivalent about sounds off the point.
@Anheuser Really, no. As I always say, @Balarka and @Akiva are near my age and much more mathematically knowledgable / mature.
On the other hand, "the people" are incompetent at making logical conclusions and reasoning. So what should be taught is logic, not debate skills.
01:22
@BalarkaSen I see, debate skills vs. debating uninteresting points are two different matters. I agree with you that forcing someone to debate something they are opposed to is definitely off point.
@MeowMix It is best not to compare ones own achievements to those of others, based on age. You could spend a lifetime in despair with those thoughts.
Instead, they shouldn't be arguing for the contrary point, but seeking to do a study of it and determine what merit the opposing side can see.
@BalarkaSen Formal logic?
@Anheuser Generally, logic of any variety suffices if they're taught to generalize the system.
@BalarkaSen @Axoren Honestly, the education system in North America is in ruin.
01:23
College = too expensive
Shit, I really need to write this essay
Agreed. I actually believe that a logic system should be taught before algebra, because it seems kind of astounding that children are expected to just get it.
Yes!
I managed to be one of the ones who did, but looking back, I can't fathom how.
There definitely should be a course in logic, perhaps as a subset of the mathematics curriculum, for every year in high school in increasing order of complexity/abstractness. And the rest of the syllabus should draw frequent references to logic in that specific grade.
You know, I understood it as well. But absolutely hated it. I would not study, I wouldn't do any homework. I failed grade 11 and 12 and graduated with an average of 65%.
01:25
I'll either sleep or talk in math
@BalarkaSen I think so too.
Or do Ted-cercises
Logic is more beneficial because it allows people to find flaws in reasoning regardless of context. You'd solve so many deep and philosophical Facebook posts if you just educated the common man in basic logic.
Maybe even then, Shaq wouldn't believe the world was flat.
Shaquille O'Neal?
I learn something new everyday...
I d-d-d-didn't stutter, did I?
Lol
01:27
Pretty sure that was a practical joke
I used to believe that I had special powers in grade 1. If I flexed my hand a certain way I believed I could control others minds!
This of course, is not possible.
Or is it? vsauce music plays
Even I find myself using logical falacies, sometimes. Because when I was younger, they taught me how to find the roots of a 2nd-degree polynomial instead of logic.
On the other hand it's just an utopia. Even if there was logic, the teachers - most of them incompetent at logic themselves - would teach those chapters mechanically and make it seem like the logical ideas are a rule of thumb which can only be applied to the math test, not the physical world.
So, like, whatever
My math teachers weren't even enthusiastic about math.
01:29
The roots of a 2nd degree polynomial by factoring?
@Anheuser Or completing the square...
I'd ask if I could show them something cool that would relate to what we were doing, and they'd say no
@BalarkaSen One of the biggest problems with lower education is that the teachers are not specialized in the subjects they teach. With only a valence understanding of each topic, they can only teach from their curriculuum as written, not as intended.
In fact, my grade 6 teacher was such a bitch (excuse the language, there's no other way to describe her) I didn't self-study at all because I just couldn't stand math
@Anheuser Factor your quadratics with trig identities
@MeowMix Ah that's sad.
@SimplyBeautifulArt I use martian math.
I had to "teach myself" pre calculus, calculus and physics to get into college
because as I said my average was so low.
01:31
I'm finally going to be doing some rigorous calculus / analysis-like stuff in the near future
We need to dissolve the fact that teaching is a certificate-level position and incentivize qualified professionals to teach in elementary and secondary education positions.
@axoren my thoughts exactly.
@axoren but once I'm done my PhD, no wayy.
excuse my language.
The only problem is that in areas where the education system is failing, there's not enough funding to get anyone other than a certified "teacher"
@Axoren Why would qualified professionals teach in high schools? What for?
They can just go in a university and be a professor and do research
@BalarkaSen As of right now? Fiscal suicide. Generally, they don't even see it as a retirement option because teaching at a university is an option.
01:33
@BalarkaSen you could technically do research as a high school maths teacher, I suppose.
@Anheuser You can technically do research without being a part of any academic institution, I'm pretty sure.
Not just for money; because they can get a good environment (for their research, say). In most high schools qualified professionals don't get the right environment to teach what they want to teach and soon gets frustrated and stops interacting
@axoren Hahahahah! Yes!
@BalarkaSen Yes, but you could take some youngin' under your wing.
@BalarkaSen You graduate yet?
Have you axoren?
01:35
I'm in a PhD program right now.
Ah. How's it going?
For compsci or math?
I want to get my Ph.D.
Almost done. Comp Sci in machine learning.
Youngsters nowadays don't give a damn. "See that math nerd? I don't effing care about his math"
But I'm not sure if CS or pure math
01:36
I'm doing mine in pure math.
Pure math is scary to me.
@Axoren Nah
why because there are zero applications and the whole field seems redundant?
Eventually, you start getting dinosaur shaped manifolds with interesting properties.
haha! This is true.
Gauss' analysis of a hole in the ground.
01:37
But then you get that really scary question: "Now what?"
You know, I wake up every morning and have a coffee and right away I ask myself "now what?" and the answer is always "have a cigarette"
I've been in that practical-less hole a few times in my comp-sci studies, where a colleague of mine and I worked together to formalize a protocol for transmitting data across space-time in the time-axis.
So I've become accustomed to answering any "now what?" with "have a cigarette"
We called it Future-Safe transmission.
Huh that's pretty radical!
01:39
We spend months formalizing sending a problem into the future, solving it later, and retrieving the answer in the past, so that you didn't have to wait.
Sometimes I wonder if the work we put in is worth living. And to that I don't know the answer
The answer is to do what makes you happy, while still surviving.
Then we realized there was only one theory of time-travel in which it would work, and the whole thing became uninteresting.
And I know the exact one you are speaking of.
But cannot recall the name.
Tachy...
tachhhhhhh
Tachyons?
Because those are a theoretical* particle.
01:41
Ah. The tachyon telephone?
Yes that was what I was thinking of.
You must forgive me, I am not well versed in the realm of physics or computer science....or math for that matter.
Ahh, this is essentially the theory we were discussing, yes.
Do either of you program in assembly?
That's pretty cool though, really.
We were tackling it from a practical application standpoint. (Assume this exists, integrate it into a software platform)
Yeah it's abstract and out there but it's cool.
01:43
Or, well, what languages in general do you program in?
@MeowMix I had the fortune of only learning a little C++. I found it too easy, so I never studied, and so found it hard.
Alright.
@MeowMix Find some meaning in the stuff you do. Or try to find it. I don't know how to live through the days doing what I do without hoping for some meaning to it all... being fully aware that it's a dubious idea.
Java since Highschool. Python, but not fluently. I'm a tool of the job kind of guy, so I'll pick up a new language in a day if it has language features that make solving the problem I have easier to do.
@MeowMix I do not generally like to program, I liked doing discrete mathematics for computing, but have never liked to program.
01:44
Oh :[
@MeowMix What is your "language" of choice?
One thing for all you math programmers, there's a python library called Theano which does automatic-differentiation.
Meaning you can make any function in it, and it'll automatically calculate gradients of that function.
For scripting, Perl. For programming, MIPS assembly, followed by x86 assembly, followed by C, followed by 6502 assembly, followed by C#
Wow that's an impressive resume.
@MeowMix Please stop programming in assembly directly. That's what C and C++ are for :(
01:46
Explain to me what a limit is.
@Axoren I do ROM hacks
OH, that's fine then.
As long as you're not learning a new assembly instruction set everytime a new chip comes out.
@Anheuser It's formalizing the notion of "what does this function approach?"
I'm not too familiar with $\varepsilon-\delta$, I just know the topological definition
@Axoren I don't think the N64 will have any updates soon ;]
I knew a guy who did ROM hacks. Kid turned his SNES into a midi-sequencer because he liked their unique sound-code.
a limit tells you where you are going, but you might not end up there
01:48
haha.
it's true!
perhaps.
My first ROM-hack was a project for Ocarina of Time which generates a bijection of the item table out of a hashed version of your filename.
if you and a friend walk towards the same crack in the sidewalk
from opposite directions
And so, when you receive an item out of a chest, it's randomized
01:48
but both believe stepping on the crack will break your mums back
@MeowMix That's neat. How do you resolve deadlocks?
youre both heading towards the crack (the limit)
but never will get there
@Axoren deadlocks?
i.e. You need the hookshot to get the hookshot
that's an interesting way to look at it.
01:49
i tutored a lot of calc 1-3 lol
Well, this was specifically programmed for, well, you may not be familiar with this term, but, "speedrunners"
came up with lots of analogies
oh gosh
I've always just tied a limit to the first derivative of a function and chalked it up to the instantaneous rate of change. at x.
we talking TAS in the Math Stack chat?
I do TASes as well.
01:50
@MeowMix You don't know me very well, but I'm talking to you from my gaming rig
I also play some mean Pikachu in Melee.
oh dear
i spectate lol
KoreanDJ actually went to my university.
@MeowMix Good luck on your essay man.
@axoren thanks for the chat.
01:51
limits dont have to do with derivatives
Yeah, what if it's not differentiable?
can still have a limit lol
I know.
@MeowMix But yeah, deadlocks are important to speedrunners for the following way: A speedrun cannot be completed if there is a deadlock.
in the case i just described
not differentiable at the point of the crack
but the limit exists
01:52
Like $|x|$
sure!
or any 'removable discontinuity'
Or Weierstrass' crazy function that's nowhere differentiable
oh yeah
I'm trying to perform a sanity check. If a group G has subgroups A, B, C so that B is normal in C, what is it that can make <A, B> not normal in <A, C>?
So you'd need to take into consideration item acquisition sequencing. Each chest depends on certain items to reach them (in the case of OoT, glitches can resolve this), ensure that there exists some reachable sequence of chests before that chest which contain those items, and there's no deadlocks.
01:54
Sorry I really need to write this essay.
Nice talking to y'all
Good night.
@Xindaris not quite sure, trying to think of a counterexample
the reason I thought this worked for a moment is because B normal in C gives a natural projection map C -> C/B whose kernel is B, and it seems I can use this to define a map <A, C> -> C/B by taking all elements of A to 1, and elements of C to the same as the natural projection. and that map's kernel looks like it's <A, B>
but it seems like the most likely breaking point in an otherwise possible proof of something I have a counterexample for in front of me
What is the counterexample?
was going to say it seems to work if you used a natural projection lol
It's to do with subnormality. If H and K are both subnormal in G, then J = <H, K> is not always subnormal. But
since K is subnormal then I have a subnormal sequence K < K_1 < K_2 <...< K_n = G, and if K = G then obviously J = G is subnormal in G. So I can induct and say <H, K_1> is subnormal and <H, K> is normal in <H, K_1>, so <H, K> is subnormal in G. actually this is even worse since I don't appear to have used H's subnormality at all
this is roughly where i am at in abstract algebra, testing the limits of my knowledge haha
02:01
the counteexample to that is a kinda longwinded construction of a group where you can get two subnormal groups with series of length just 3 or so but their join isn't subnormal
I think there's something wrong with my conclusion about the kernel but I'm not sure what
usually there are algebra guru hanging around, not tonight it seems...
02:14
ok. if anyone's curious, A not normal subgroup of C, B trivial group is a counterexample. I'm going to keep working at it.
02:31
Thank you
I was, lol
02:58
@TedShifrin , I've sent many students to your youtube series
tutorees etc, great resource!
03:18
Hey @Mike!
How's everything going?
i'm probably going to reboot my sleep cycle today
To a normal one or one that's even more corrupted than what you already have?
hopefully the former!
it has happened on multiple occasions where it became the latter
03:33
Good, because it seems like as it stands, yours is so convoluted that that we can use it to approximate the identity and all
03:56
Hey @Ted and @arctic!
hi again Demonark ... I didn't know I was still here. Hi, tern.
@logical: I hope it helped.
@Balarka: Your non-sleep schedule is absurd.
lol "non-sleep schedule"
The truth is laughable, isn't it?
only when presented in the right way
04:01
Well, my losing my temper and speaking intemperately earlier to the French person who insists on asking everyone for help was probably not the right way. But I honestly don't think the graph of $|x|+|y|\le C$ is that difficult for someone doing relatively advanced mathematics :(
Demonark, are you rewriting some of Shakespeare these days?
Haha, not quite
I figured you would have your own version of Measure for Measure by now. :P
waits for Balarka to roll some number of eyes
eye have no I
Oh wait...
snaps Nice...
Hey @Fargle!
And how's it going @tern?
rolls $2^{2^{\aleph_0}}$ eyes
04:06
Hi @Fargle
Hi @Ted, @Dami, chat at large.
That'll take you the rest of your life and longer, @Fargle. Good luck with that.
So $\aleph_2$ then
And yeah that'll take longer than writing down the Borel hierarchy
OK, I'm going back to watching Netflix.
Bye, all.
@Daminark GCH intensifies
2
@TedShifrin Have fun!
04:08
Enjoy
See you @Ted!
I have to decide how to distract myself from not falling asleep
How? @Balarka
I can learn some cool math, watch a movie, listen to music or whatever
@BalarkaSen do all of them, simultaneously
04:17
Oh also our first pset in analysis just went up
Nice. How is it?
It seems pretty cool
First question is to find two matrices in $SO(3)$ that generate the free group
Second is to show that there are no finitely additive measures on $\ell_{\infty}$ for which the measure of every ball is positive and finite
hoooo boy
Third asks whether there's a countable $\sigma$-algebra
(countably infinite)
lol I was gonna say.
04:20
@Fargle Learning foliations while listening to death metal and watching slasher films? bad idea
$\{\emptyset, X\}$
4 says to characterize the $\sigma$-algebra generated by sets of the form $(-\infty,a)$
@BalarkaSen I was thinking learning <insert math topic I don't know about yet here> while listening to show tunes and watching avant-garde festival films.
Last is to show that the set of points where a function is continuous is $G_{\delta}$
$G_{\delta}$ is countable intersection of open sets, right?
04:22
Yup
That seems like it wouldn't be too bad, but then again, simple statement $\neq$ simple proof.
It essentially follows from the oscillation definition of continuity
I know that one since Soug gave it to us as a bonus problem first quarter
Well
I'm unfamiliar with that one, at least by that name.
The problem was to show that no function could be continuous just on $\mathbb{Q}$
Ah, yeah, and $\Bbb Q$ isn't $G_\delta$.
(Though, it is $F_{\sigma}$.)
04:26
Yeah
But yeah so in the case where $f:\mathbb{R}\to\mathbb{R}$
God thank you finally
An F from R to R for once god damn
The oscillation of $f$ at a point $p$ is $\lim_{\delta\to 0} \sup_{(x\pm \delta)} f(x) - \inf_{(x\pm \delta)} f(x)$
And a function is continuous somewhere if and only if its oscillation is $0$
Lol @Mick seen too many rando functions?
Well I have to finish up a proposal that works in a nice medley of finite fields, and then when I come here it's always some crazy groups that leave me feeling like I wouldn't question it if a physical fucking apple was one of the elements
what are bivectors?
l m a o
And @cows beats me
04:39
@Cows If $V$ is your vector space it's an element of $\bigwedge^2 V$.
I mean you'd think Z is all the numbers, but then you're like oh! in-betweens! boom Q no problem.... but wait, in-between those in-betweens... ok fine.... R... but wait! NO. NO WAIT JUST R. R.
I have been thinking about what it means to be a fermion , and I keep running into bivectors
@MickLH It's almost surreal. hehehe
@BalarkaSen it's a little late
@Fargle Your quotes are gold today
04:49
It's morning here
@Daminark Always happens when I'm very tired.
alright alright
I didn't sleep all night and planning on pushing through till tonight
and fix everything
Eek, good luck with that @Balarka
And lol @Fargle come on the chat more when you're tired :P
@Daminark It leads to just as much bad mathematics as it does good quotes.
04:51
$\mathbb{C}$ is a conspiracy. It's actually just $\mathbb{R}^2$
I disagree
I feel like, after a long week of little sleep, you'd find me arguing that $|\Bbb Q| = |\Bbb R|$ against Ted.
@BalarkaSen You, disagree?
I do. $\Bbb C$ has a natural complex structure on it; $\Bbb R^2$ doesn't :)
No, no--$\Bbb R = \sqrt{\Bbb C}$.
That just has me considering: I know it's possible to extend $X^J$ to arbitrary sets $J$, but is it possible, or for that matter, even sensible, to extend Cartesian powers to, say, any real number?
05:31
Last night dream: Saw a strange algebraic system which seemed to have some kind of topological properties:

Given
$ax=x$
Multiply on the right by $x$
$(ax)x=xx$
Then
$x=x^2$

The above is the example in the dream, which is quite straightforward as a and x form a pseudoinverse. However, there's an implication that the dream use this example to illustrate, and it is the following:
Consider the string of elements:
$axxxxcxxb$
This algebraic system has an unusual axiom that
$a(any 5 elements)c=e$ where $e$ is the identity

Therefore if you have $axxxc$, it does not simplify under this rule. However, if you have $axxxxxc$, then it becomes $exxxxx=xxxxx=x^5$
In a sense, it is a generalisation of pseudoinverse, a "position dependent" pseudoinverse
Of course, we can go even further: Let a string of elements $s$. There's an axiom $a(\text{some string from a set S})b=c(\text{some string from a set S})$
Now if $xxxxx=y$, then one can see something interesting because $ayb=cy$ but $axc$ stays as $axc$
meaning that for the special case where elements combined to form the identity, you now hae selective pseudoinverse, and more generally, you have algebra that is dependent on the position in the string
More investigation is needed to determine what are the axiomatic systems required to preserve associativity
Now, because of the position dependent nature of operations, this means one can easily encode a topology in this algebraic system because the string only simplify if the elements are in the correct relative positions
06:16
I also suspect that the following:
17 hours ago, by SteamyRoot
@Vrouvrou Translation invariance means $d(x+a,y+a) = d(x,y)$
is the inspiration of the dream, because moments after the ax=x example is shown, the teacher than asked what is a+x
06:28
Sup guys
Anyone in the mood for Statistics & Probability? :D
06:48
maybe, just ask
06:59
Hi @Alessandro
08:34
Downvoted. I am trigger happy for any OP that ask people to do their work for them, or worse, ask people to to their friend's work for them
 
2 hours later…
10:44
@TedShifrin "tourner" would be much much more colloquial. Except in the phrases "virer de bord", "virer à droite/gauche", people will understand "virer" as "remove" or "throw away"
Salut
Hi, I am a discrete math noob and I have a following question:
Given numbers from 1,2,3,...,10 , if we are allowed to pick 3 of them, in how many cases does the sum of those numbers a) equals nine b) is less then one ???
b) is quite straightforward is it not ?
Obviously, those sums are: 5+3+1, 4+3+2 and 6+1+2, but what is the method use to solve this problem?
*sorry, by b) I meant less then nine
It depends how you consider the numbers
If order doesn't matter, then it's just 3
Else you have to take into account the different permutations of these numbers
ie multiply the result by 6
10:49
yes, it does not matter....I recognize it has to do with partition of numbers where there will be 3 disjoint sets with those sums, under the equivalence relation
But you have the result don't you ? What are you struggling with ?
the result is 3, that's ok, I want to know the method, imagine if the question replaced 9 with, for example, 567, it would be much more difficult
Well you chose, say, the lowest number
Then remove that number from 567
It gives you another number, and you need to chose two numbers of which the sum is that new number
For instance 567
Chose 1
You get 567-1 = 566
Then you get 2+564, 3+563 and so on
sure, but that's the sum of two numbers, I need 3 :)

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