Mathematics - 2013-01-30 (page 2 of 3)

skullpatrol

16:00

A quiet crowd...

Ed Gorcenski

shhhh

I'm thinking

robjohn

@EdGorcenski >crash<

Ed Gorcenski

You made me sneeze! There goes my proof.

robjohn

@EdGorcenski sorry. What were you proving, before I so rudely interrupted?

Ed Gorcenski

That this thing is in fact a sausage and not a pretzel

boston.com/sports/hockey/bruins/extras/bruins_blog/2013/01/…

Not sure how anyone thinks that's a pretzel. Clearly a sausage.

robjohn

16:14

@EdGorcenski could be a hot dog...

skullpatrol

...or a cold wiener.

Ed Gorcenski

Is a sausage not just a generalization of a hotdog?

skullpatrol

Either way Boston doesn't have much to talk about since the Patriots got knocked out.

Ed Gorcenski

Et tu, skullpatrol?

robjohn

@EdGorcenski I think of them as different things, but I guess a hot dog is a weird type of sausage

@skullpatrol all of them? have they been checked for concussion?

Ed Gorcenski

16:21

Bernard Pollard hit Stevan Ridley so hard he knocked out the entire city.

robjohn

@EdGorcenski wow.

skullpatrol

True dat^

Ed Gorcenski

Either way, hockey is where it's at, and Boston is a hockeytown. At least it is when the Red Sox are the comedy show they are these days.

skullpatrol

The Ravens are HUNGRY!!!

a shortened hockey season turns a hockey town into a hockey village ;-)

Orange Harvester

@robjohn Half angle expansions?

@EdGorcenski Weren't there concerns about life long injuries caused as a result of sacking? (That's the right word for bringing the player down right?)

Ed Gorcenski

16:36

No, a sack is different

There is a lot of ongoing concern about injuries as a result of hard contact to the head

Often times players tackle by leading with their helmet, leading to helmet-to-helmet contact

Also, players carrying the ball often lower their head to "plow through" to gain a couple extra yards, this exposes the head to impact

There is a high risk of concussions, some tests show forces on the head well in excess of 100 Gs.

The syndrome that has been studied is known as Chronic Traumatic Encephalopathy (CTE). It's marked by an accumulation of tau proteins in the brain, but so far it can only be diagnosed posthumously by brain dissection

Essentially, it's permanent bruising to the brain from multiple high impact blows to the head.

skullpatrol

@OrangeHarvester What you are referring to is called "getting your bell rung"

Ed Gorcenski

I think he was referring to "tackling" in general.

Orange Harvester

@EdGorcenski that's crazy.

Ed Gorcenski

@OrangeHarvester A "sack" is when the quarterback is brought down behind the line of scrimmage. This is usually hard to do (a team will do it about 3 times a game, if they're very good), so it's a big deal.

Orange Harvester

@EdGorcenski I was referring to tackling in general. Actually, I had seen that movie, "Rudy" I guess, where I learnt the word.

robjohn

16:49

@OrangeHarvester that works

Orange Harvester

@robjohn cool.

robjohn

@OrangeHarvester how would you use them to get that result?

skullpatrol

@robjohn Your Stanley Cup Champion LA Kings put on a clinic for the Vancouver Canucks on how to come back and win from being down 2-0 the other night.

Charlie

@skull :D

skullpatrol

@Charlie :D

robjohn

16:55

@skullpatrol How nice of them...

Orange Harvester

@robjohn I am not exactly sure. Let me work it out a little.

@Charlie yo.

robjohn

@OrangeHarvester sure. I'm not pushing. It's a nice problem.

Orange Harvester

@robjohn Yes. It is. How did you do it?

Charlie

@skullpatrol ;)

skullpatrol

@Charlie ;)

Charlie

16:58

@skullpatrol just came by because of your song

skullpatrol

@Charlie Did you like it?

Charlie

@skullpatrol yes

skullpatrol

@Charlie :D

Charlie

@skullpatrol any other you may like to share?

@OrangeHarvester hi

Orange Harvester

@Charlie Wassup?

Charlie

17:02

Nothing new

skullpatrol

@Charlie I haven't heard this for awhile?

Ed Gorcenski

This question arises again! math.stackexchange.com/questions/290687/…

Orange Harvester

fuuu. It seems like the start of algebra courses all over the world

Ed Gorcenski

yep

Orange Harvester

is there not an exact duplicate?

Ed Gorcenski

17:07

it is. I don't care enough to find it, though.

I mean, 2 days ago we solved this problem in chat.

Charlie

@skullpatrol I really like this song!

skullpatrol

@Charlie :D

user19161

Oh well, I deleted the answer which was downvoted, again without comment. It's OK but maybe the downvoter thought it was not elegant.

Charlie

@JasonBourne hi again Jasbear!

user19161

@Charlie Hey.

user19161

17:12

I am quite upset with the downvotes I got this month. I think the answers are OK.

skullpatrol

Don't get upset....

Charlie

Hava nagila, hava nagila , hava nagila venis'mecha

@JasonBourne :)

user19161

@skullpatrol Yeah, they probably can't appreciate my answer, their loss! =)

skullpatrol

@JasonBourne you got that right pal :)

Charlie

@JasonBourne I like your answers, Jaspy.

skullpatrol

17:20

Me too.

user19161

In other news, it seems that the users on Eng and TeX that I upvoted get to keep their rep.

user19161

I guess TPTB figured there would be a massive loss if they removed the votes, so they somehow deleted my accounts without deleting the votes.

user19161

That is also why I still get to keep the association bonus even with just one account left.

skullpatrol

@JasonBourne Have you heard the Stackexchange "Podcast"?

Orange Harvester

@JasonBourne Good!

user19161

17:23

@skullpatrol No, is it related to what I mentioned?

Orange Harvester

It is possible that in case, you rejoin in future, they might reset your rep to the value you had when you left.

skullpatrol

Not really, but it gave me some interesting insights...

user19161

@OrangeHarvester Yes, maybe they have a way to delete like that.

user19161

Maybe they are trying to be really nice to me, so I appreciate it.

user19161

@skullpatrol Such as?

skullpatrol

17:26

@JasonBourne The politics and policy of this website.

user19161

@skullpatrol Ah, well, no system is perfect.

user19161

If problems arise, we try to resolve them.

user19161

But in some systems, the problems get too big for some people.

user19161

So those people decide to abandon those systems, whatever they are.

skullpatrol

@JasonBourne True dat

user19161

17:27

For me, I have already mentally abandoned some systems...

skullpatrol

@JasonBourne Here if you're interested.

robjohn

@JasonBourne: I have no idea why this was downvoted

user19161

@robjohn Well, some details I edited in, so maybe they were not happy with it before, but still, a downvote without comment is weird, but never mind.

robjohn

@JasonBourne I hate downvoters who don't explain anything, but that is just the way things are.

anorton

@robjohn what was downvoted? I see +5, +7, and +3, but no downvotes. Or is it a deleted answer?

robjohn

17:38

@anorton It was deleted.

anorton

@robjohn oh. ok. I guess I have to wait a couple years to see it, then. ;)

robjohn

@anorton you think it will take that long to get 10K?

David Wheeler

i'm hoping i never reach 10k. i would shudder to think people might believe i actually knew anything. i practice "jazz math" it's all improvisation.

anorton

@robjohn maybe. I don't know as much math as a lot of the 10k people here, especially since I'm going to be an engineering student... It limits how many answers I can give.

user19161

@DavidWheeler Well, I am lucky. I have a few fans here. =)

anorton

17:42

But I have time to reach 10k, too... I'm just in my senior year of high school.

user19161

@anorton Oh great! Are you gonna major in math?

David Wheeler

ugh. fans. the idea of people fawning over me is distasteful.

Charlie

@skull I made a portrait of you

skullpatrol

@Charlie Oh, really?

user19161

@skull Will we ever know your identity?

David Wheeler

17:44

@anorton may the force be with you.

anorton

@JasonBourne I'd love to, but I don't know what I'd do after graduating with a math degree. I don't know if I'd like to be a professor/researcher all my life. I've got to look in to it a bit more...

user19161

@anorton Yeah, think carefully before deciding. Having said that, one's perspectives change over time.

David Wheeler

@anorton you could be an applied mathematician....always a high demand for those.

Ed Gorcenski

@anorton Many things can be done with a math degree

Having a strong background in math allows you to branch out to many, many fields.

user19161

@EdGorcenski For example, you can use the paper as toilet paper.

2

Orange Harvester

17:46

Even computer science.

Ed Gorcenski

Unfortunately, academics really only present two options to students: academia, or not academia.

anorton

True. I do like CS, especially algorithm analysis.

Tobias

more and more companies are realizing that a degree in math makes you, in many respects, a jack of all trades, as you have learned a pattern of thought that is applicable to so many situations

Ed Gorcenski

There's all sorts of stuff: government, industry, big business, small business, non-profit reseach

Exactly what Tobias said

skullpatrol

...doing more math...

David Wheeler

17:48

@anorton one of the benefits of learning "more math" is something rarely talked about, per se: an ability to think clearly. this is valuable no matter what day job you wind up in.

3

anorton

I took Princeton's Algorithms class on Coursera, and enjoyed the mathematical components thereof. I'm now taking the Analytic Combinatorics class on that site, too.

robjohn

@anorton There are a lot of questions that don't require a lot of prior knowledge, just a bit of logical thought. You may get there faster than you think.

Orange Harvester

@anorton Even I am taking the same! May be we can take it together?

user19161

@DavidWheeler But I wanna add that mathematicians have a tendency to go nuts and then they think unclearly.

David Wheeler

yes, that can happen. dabbling in some artistic endeavor to keep you sane is recommended.

anorton

17:50

(too many people to respond to at once! :))
David: I have found that the more I do math, the more logical my thinking processes become. They also become more detailed, which causes some difficulty in other areas of thinking. :)

Orange: the Combinatorics class on Coursera? I'm in the one going on now...

RobJohn: I guess so... 10k just seems like such a big number...

David Wheeler

@anortan indeed. so something that forces you to think "holistically" is a good antidote.

anorton

@David Yeah. I just enjoy math a lot more than the stuff that forces me to think holistically.

David Wheeler

zoom is good. able to change zoom level is also good.

anorton

@DavidWheeler A lot of people are telling me that now... :)

Orange Harvester

@anorton Yes, I am talking about the one that is starting on Feb 4.

anorton

17:53

@OrangeHarvester Cool! :) It's amazing I've run into someone who's in the same class.

Got to go... class about to start...

Ed Gorcenski

man, got a pneumonia vaccine today, shoulder hurts like a sonuvabitch

Orange Harvester

@anorton :D Bye. See you later.

David Wheeler

most sob's i've known seem to be in pain...hence their non-empathic behavior

skullpatrol

@Charlie may I see it?

Hi @MarianoSuárez-Alvarez how are you?

crispyfriedchicken

Hi. If I expanded (A OR B) AND (C OR D), is it equivalent to (A AND C) OR (A AND D) OR (B AND C) OR (B AND D)?

Ed Gorcenski

18:09

Yes

skullpatrol

@Charlie ;)

Ed Gorcenski

Easy to verify -- if any term in parenthesis on the right hand side is true, then the left hand side must be true.

David Wheeler

the distributive rule rocks. <---my proof.

skullpatrol

You can't prove a statement that is accepted as true.

David Wheeler

i know what you mean....$a = a$ has been giving me trouble for YEARS

skullpatrol

18:15

;-)

If a is a real number, then $a=a$

Charlie

skullpatrol

lol^

Charlie

@skullpatrol looks like you :D

skullpatrol

@Charlie thanks :D

Charlie

@skullpatrol :D

skullpatrol

18:20

Charlie

@skullpatrol NICE!

@skullpatrol is it yours??

skullpatrol

@Charlie No, I just found it on the web...

Charlie

@skullpatrol really cool

I drawed that, but the vertebral arch is wrong

skullpatrol

I don't like the helmet shape though.

Charlie

hehe

skullpatrol

18:24

hoho

Charlie

huhu

skullpatrol

hihi

Charlie

haha

skullpatrol

and sometimes hyhy

Charlie

Are you lonesome tonight,
do you miss me tonight?

skullpatrol

18:29

Elvis?

Charlie

@skullpatrol yes!

skullpatrol

I never caught a rabbit..

@Charlie and ?

David Toth

Does identity arrow in categories need to be an identity function or not? E.g. is 1R:R->R, 1R(r)=2*r considered an identity arrow although it is just bijection and not an identity on a set of the reals?

Charlie

@skullpatrol and what?

skullpatrol

@Charlie what is the next line?

Charlie

18:31

@skullpatrol are you sorry we drifted apart?

Does your memory stray to a brighter sunny day

skullpatrol

Is your heart filled with pain? Shall I come back again?
Tell me dear, are you lonesome tonight

Charlie

@skullpatrol uuu uuuuuu uuuuu

skullpatrol

I meant what is the next line after: "I never caught a rabbit.."
@Charlie and ?

Charlie

you are a friend of mine :D

skullpatrol

yes!

Charlie

18:37

Well, it's one for the money, two for the show
Three to get ready, now go, cat, go

skullpatrol

and
no

Charlie

@skullpatrol no what?

@anon I didn't recognize you with your new haircut

skullpatrol

Goodness

anon

i.e. glorius golden bedhead?

skullpatrol

@anon ??? is that you???

Tobias

18:42

Does anyone know a nice simple way to construct a solvable group of a given derived length?

Charlie

@skullpatrol haha

@anon yup

anon

@Tobias Quotient a free group by G^(n), I think.

David Wheeler

@DavidToth $x \to 2x$ is not an identity arrow. arrows in categories need not be functions.

Tobias

@anon woops, I meant finite (which that is not, right?)

anon

...probably not.

Tobias

18:45

also, is it trivial to check that the chain of derived subgroups of a (non-abelian) free group does not stabilize?

anon

trivial is relative

Tobias

easy then

Charlie

easy too

anon

If it does stabilize at k, then [x,[x,...,[x,y]]...] (k terms) is the identity. If you pick generators x,y I think you can show this is not the identity in a free group. (On more than one letter obviously.)

Tobias

@anon why is that the identity?

anon

18:48

it would be the identity if the derived length is less than or equal to k, since that element is in G^(k)

Tobias

@anon stabilizing is not the same as the derived length being finite

anon

oh, derp

skullpatrol

@Charlie I have not seen a 10 hour song till now.

Charlie

@skullpatrol there are a lot of these on youtube

skullpatrol

hmm..

kahen

18:56

@skullpatrol pretty much any memetic video has a 10 hour video on youtube. Amazing Horse, Nyan Cat, Epic Sax Guy...

Charlie

@skullpatrol I'm listening to this

@kahen taking the hobbits to Eisengard...

skullpatrol

@kahen Thanks

kahen

And Caramelldansen, and... and...

Charlie

@kahen I always read your name as "Kraken" :|

kahen

it's an abbreviation of my real name.

and apparently markdown doesn't work in chat

Charlie

18:59

@kahen Nice name, btw

kahen

Yes. I couldn't imagine being called anything else. Weird how that works, isn't it? :)

David Wheeler

um, isn't the commutator subgroup of a free group freely generated by the commutators of the generators, giving another free group of even larger rank?

Tobias

@DavidWheeler the commutators of the generators are not enough

hmm, actually, the commutator subgroup of a non-abelian free group is not finitely generated, is it?

(I recall this being a typical example of a non-fg subgroup of an fg group)

David Toth

@DavidWheeler But $x \to 2x$ can be an identity arrow if we have a category with objects being sets? Or every identity arrow has to be an identity map if I have chosen my arrows to be maps?

Charlie

@skullpatrol did you listen the music?

David Wheeler

19:06

oh yeah, you need the commutators of powers of the generators

skullpatrol

@Charlie Yes, it was very beautiful.

Charlie

@skullpatrol :D it's a playlist with 12 wonderful songs

skullpatrol

@Charlie I like "playlists" I wish I had more time to listen to them all...

Charlie

@skullpatrol well, music is music, you just gotta let it penetrate you, no need of time, time stops when you listen to it

David Wheeler

@DavidToth that does not satisfy the defining condition of an identity arrow $f$: that $f \circ g = g$ and $h \circ f = h$ for all appropriate $g,h$

free groups hurt my head: in F2 we have a subgroup isomorphic to F3, in that, we of course have a subgroup isomorphic to F2 again. in THAT, we have a subgroup isomorphic to F4, and we can keep this up all day long, always taking subgroups which have larger rank free groups inside them. they're just "too badly infinite"

Charlie

19:23

@jason HI!

Tobias

@DavidWheeler yeah, stupid free groups and their counterintuitive behavior

user19161

@Charlie Yo, I think I should come to this chat less often. =)

David Wheeler

free group problems are "Not-David-complete"

Charlie

@JasonBourne why jaspy?

skullpatrol

@JasonBourne ya why?

Charlie

19:31

@jason why you don't reply?
answer to us , we want to know why

come on, don't be shy

Orange Harvester

reply, reply

Charlie

@jasonBourne if you leave, you will make us mourn

through the days and through the nights,
while you are out of sight

skullpatrol

he is afk

pourjour

hi

skullpatrol

lo

Charlie

19:38

@skullpatrol I am just writing

anorton

mid

Charlie

@pourjour hello

pourjour

@Charlie how are u?

Charlie

@pourjour not splendid

skullpatrol

u are how?

pourjour

19:39

@skullpatrol I'm fine tnx and u?

skullpatrol

Fine thanks.

pourjour

@Charlie why :0?

skullpatrol

ya why?

Charlie

@pourjour hmm nothing specific, actually, you know those days when you feel "not ok"

pourjour

@Charlie yeah true story

Charlie

19:43

@pourjour yeah...

@pourjour Any questions for today, Soufian?

pourjour

@Charlie nah, I'm in vacation

Charlie

Soufian sounds like a whistle

@pourjour yeah!

pourjour

@Charlie any news?

anorton

Side note... this was an interesting integral to solve without trig sub: math.stackexchange.com/a/290797/23353

Charlie

@pourjour no... you??

pourjour

19:48

@Charlie I will back to school after 4 days (sad news)

Charlie

@anorton huuu

anorton

?

Charlie

@pourjour ow, you don't like school either?

pourjour

@Charlie I think it's not the appropriate way for learning

anorton

@Charlie Maybe I'm not reading it right, but "huuu" doesn't ring a bell...

Charlie

19:49

@pourjour hmm...

pourjour

I just waste my time there

Charlie

@MichaelCorleone Che cosa stai facendo?

@anorton then nevermind

anorton

oh

Michael Corleone

@Charlie Niente

or is that wrong haha

Charlie

@MichaelCorleone it's right haha

@pourjour ow... you don't learn anything cool?

Geez..only I liked school...

skullpatrol

19:54

if?

Charlie

@skullpatrol ?

pourjour

@Charlie especially school here are useless

Charlie

@pourjour sometimes I got pissed off, but now I realize how many nice things I learned there :)

pourjour

@Charlie I like to assist math class, it's where I learn new things

Charlie

@pourjour that's a good thing

Ethan

19:58

A

Orange Harvester

B

Ethan

C

D

Orange Harvester

E

F

Charlie

@pourjour I did this

Ethan

G

anorton

19:59

H

Orange Harvester

I

Ethan

J

anorton

K

pourjour

L

anorton

M

Charlie

19:59

M

Ethan

N

anorton

$\mathbb{O}$

Transcript for

$Mathematics$ Mathematics