Mathematics - 2013-03-17 (page 2 of 3)

3:01 PM

show it takes positives and negative values

as you know limit for norm to infty is 0

you can chose a compact subset such that ever value outside of it is bigger than your negative and smaller than your positive bound

as your function is continuous use that continuous functions attains minimum and maximum on compact sets

Michael Corleone

Ok thanks I was thinking of something like that but wasn't sure how to do it

user19161

3:16 PM

@peter What do you think of my answer here? Is it clear? math.stackexchange.com/a/332790/4594

Peter Tamaroff

"if x∈B, then x∈B" NO SHIT! =)

user19161

Oh let me make some edit, I just realised I got confused...

Dominic Michaelis

i used at first lim insteadt of limsup and liminf here math.stackexchange.com/questions/332843/…

kram1032

Hi there. I just had an idea for a voting system and now I wonder how to pull it off. It would be voting on quantitative values rather than qualitative separate categories and the idea to have votable presets and the elected result would be a compromise.

Do you know of anything like that?

For instance, the system could be used to democratically vote for a tax plan or something like that.

user19161

@PeterTamaroff OK I edited, it is good now!

Dominic Michaelis

3:23 PM

you mean like amazon where you can chose between 1 star and 5 stars ?

kram1032

no, not rank-voting

rather, you have different options to vote on, like, say, taxes of 8%, 10% or 12%

you vote for one of them, and the result of all collective votes should be the "most agreeable value" in a democratic sense

But since numbers exist on a continuum, you wouldn't restrict yourself to the three proposed models, but rather weight between them to obtain a "most agreeable compromise" of, say, 9% taxes

user19161

@PeterTamaroff Damn I feel so stupid for posting what I did!

kram1032

(maybe taxes aren't the best example but I hope it's clear what I mean)

Peter Tamaroff

@JasperLoy Why?

user19161

@PeterTamaroff Well, I just realised the question is much easier than it looked. The asker confused me!

Karl's students

3:28 PM

@JasperLoy: Please check your inbox (your email).

kram1032

I wonder if such an automatic compromise technique already exists, other than simple per-voter-weighting.
The given example really isn't that great but I could imagine having more complex scenarios, where simple weighting might cause biases you wouldn't necessarily want

user19161

@Karl'sstudents WTF! Is that so private you have to use email?

Karl's students

@JasperLoy Yes. It is a big problem.

kram1032

(In a way, I'm asking for voting techniques working on histograms that translate to continuums. The histogram buckets are the typical choices in a normal, qualitative election)

user19161

@Karl'sstudents I think it is not really a sensitive matter, so I will reply to you here. Just use your real name then if you want a reply from Herbert, end of story...

Karl's students

3:31 PM

@JasperLoy QED

user19161

@Karl'sstudents Yes, would be good if you tell us more about yourself too. You might be an alien from another planet for all we know...

Charlie

@jasper hi! You are back to my favorite blue!

Karl's students

@JasperLoy No. It is impossible.

Jayesh Badwaik

@kram1032 Though I am not sure what you to say, there are weighted voting methods which can be quite complex. I was once an organizer in student election. The system was that we had to rate every candidate as we liked between 1-100. And then using a series of calculations on the relative scores of the candidates in a single vote, and the relative scores by the different student, a complex metric was formed from normal distributions and all, and then finally a single number was calculated.

user19161

@Charlie Also amwhy's favourite, also my favourite.

Dominic Michaelis

3:32 PM

@charlie you are back as my favorite person (beside jasper)

user19161

@DominicMichaelis Hehe, when are you two getting married? =)

Jayesh Badwaik

@DominicMichaelis I thought I was your favorite person. :-(

Dominic Michaelis

@jayeshbadwaik oh i like you too :)

Charlie

@DominicMichaelis why "beside jasper"? ;)

user19161

@Charlie Because we are gay, hehe.

user19161

3:34 PM

Oh man, I feel really stupid for posting such a stupid answer just now, even though it is correct.

Charlie

@JayeshBadwaik take that jayesh , I AM his fav :P

Frank Science

Have you read Pugh's?

user19161

-6

Q: Finding take-off speed.

I am completely innumerate. Please help me. My girlfriend jumped from the roof of a 110 foot building. She landed 20 feet from the building. What I want to know is if she just kind of jumped, or if she got a running start and hit the edge at a full sprint. I suspect the latter, because the avera...

linear-algebra

user19161

-3

Q: calculating speed from 32 ft per second squared fall and 20 ft distance

This is a grim request. My best friend committed suicide by jumping from the roof of an 11 story building. She landed about 20 feet from the building. Assuming it's 110 feet tall and the wind was negligible, how fast was she running (mph) when she jumped? Like I said, it's grim, but thanks anyw...

geometry physics

Karl's students

@JasperLoy youtube.com/…

Jayesh Badwaik

3:37 PM

@FrankScience Skimmed through it.

kram1032

that does sound complex. Though I wonder about a continuum of choices, rather than discrete, seperable ones. Rather than voting for some kind of ruler, it would be on voting for a particular set of numbers in an else generic law.

Another example could be age-restrictions. "At what age should x be available." answers could range from "at birth" (always) or "not until death" (never). People can vote in that range as they think, but the final voting result would not be the most often-named value but rather some sort of "as fair as possible" weighted value.

Charlie

@DominicMichaelis how are you, Dommy?

Frank Science

@JayeshBadwaik Is that suitable? I feel like that part of Baby Rudin is really tough.

Dominic Michaelis

@charlie i am fine and how are you ?

user19161

I have flagged and downvoted both questions.

Dominic Michaelis

3:39 PM

@jasper flagged them all as offensive

Jayesh Badwaik

@FrankScience If you are referring to the chaper 2 of baby rudin, it is tough, and you might want to pick up something else just for the topology stuff. But if you are thinking about the later stuff, pugh can be easy, but I prefer you stick with Rudin, it is not too difficult and will be worth it.

Charlie

@DominicMichaelis I am good :)

Frank Science

@JayeshBadwaik Eh, are you sure? I'm going through the rank theorem.

user19161

@DominicMichaelis Well, I would not call it offensive, but as long as it is flagged, it is alright.

Jayesh Badwaik

@FrankScience Rank Theorem is a Linear Algebra thing and rudin does it badly, learn it somewhere else. :-)

Frank Science

3:41 PM

@JayeshBadwaik Not a stuff of Linear Algebra.

user19161

So first we have penis questions last week and suicide questions this week, very interesting!

Jayesh Badwaik

@FrankScience wait which one are you talking about?

reference?

kram1032

@JayeshBadwaik It would be easy to just go with some statistical value like the mean or median, but I wonder whether that would be fair. - in particular, if you know it's the mean and you know, people tend to think, the appropriate age access is really low, but you think otherwise, you could fairly easily alter the result by giving a ridiculously high value. - Also, in the mentioned case, "never", simply ranked as "age infinity" would break the simplest statistical ideas.

Frank Science

@JayeshBadwaik The theorem is very long. Page 229 of Baby Rudin.

Dominic Michaelis

@jasper that sounds gay but i like penis questions more than suicide ones

user19161

3:42 PM

@DominicMichaelis Haha, yeah I like penises too. =)

3

kram1032

@JayeshBadwaik It should be some kind of voting system, that is robust against attacks like things like the "spoiler problem" in normal voting systems

Charlie

@jasper you think everyone will marry me, huh?

user19161

I hope nobody flags my starred message above. =)

user19161

@Charlie Yes, maybe Jayesh or Dominic or skullpatrol.

Karl's students

@JasperLoy I think I need to click the flag button. :D

Dominic Michaelis

3:45 PM

finally some lhf for me math.stackexchange.com/questions/332868/…

user19161

By the way @dominic I think that bull's penis is a Chinese delicacy, not that I wanna try it...

Charlie

@JasperLoy eh?

Dominic Michaelis

ah i got a joke for this one

user19161

@DominicMichaelis 6 votes in 10 min!!!

Dominic Michaelis

a tourist is in spain and goes to a noble restaurant, he is asking for the best meal they have

Frank Science

3:46 PM

@JasperLoy I think that's no interesting.

Dominic Michaelis

the waitress tells her that is it the testicles of the bull died in the arena today, the tourist says i will try it

next week he goes in the same restaurant again, and buys the same meal, after he finished, he said, this was really good, but last week it was much more

user19161

@Charlie Yes, my 3 guesses. =)

Dominic Michaelis

the waitress says, the bull doesn't lose every time ...

user19161

@Karl'sstudents Where did Herbert tell you that?

Jayesh Badwaik

@FrankScience Ahh, I see. I am not too sure about the multi-dim stuff. I used different books for it. Rudin, Dineen, Not too sure about Pugh in that case.

Charlie

3:50 PM

@DominicMichaelis is this a joke?

kram1032

@JayeshBadwaik while the "spoiler problem" probably doesn't apply to such continuous categories, I'm pretty sure there are other attacks if you choose to use simple averages and such. As mentioned, means suffer from extreme outliers, so the result wouldn't be closest to what most people actually want.

Karl's students

@JasperLoy PSTricks' mailing list.

user19161

@Karl'sstudents What name did you use?

Dominic Michaelis

@charlie it should be a joke at least :)

Charlie

@DominicMichaelis aaah I'm going for lunch, see youses

Dominic Michaelis

3:51 PM

@charlie see you :)

Jayesh Badwaik

@kram1032 Fairness of a big enough election depends much more on extraneous factors than vote calculation. For any big enough community, the danger of bias creeping in from some sophisticated method is usually more worrisome than the fairness of election, and hence, generally at the most a ranking system of candidates is used.

@DominicMichaelis you just destroyed my appetite for dinner.

Dominic Michaelis

oh sorry :(

Karl's students

@JasperLoy GC for the last greeting after best regards, but the e-mail account is the same as what I use to make correspondences with you.

leo

Hi all!

@peter

Peter Tamaroff

@leo $\sup$?

user19161

4:05 PM

@Karl'sstudents Why can't you just tell people your first name then? It's not as if they can identify you that way... There are a million people named Jasper for example in the world...

Karl's students

@JasperLoy Oh my ghost. It is a difficult option. :D

user19161

@Karl'sstudents In fact, since you won't tell me anything else, maybe I should not talk to you anymore...

Karl's students

@JasperLoy Ha?

leo

@peter how was the answer

Peter Tamaroff

@leo Oh, I read it when I woke up this morning, but I think I was still too sleepy!

I'll read it a few times.

@leo Why do you say "large enough set", for example?

leo

4:15 PM

@Peter if the set is, say, finite we will not have enough variables :-)

Peter Tamaroff

@leo I see.

kram1032

yeah, that's partially what I'm wondering. Let's take a fully continuous case. In the simplest case, voters may choose any real value from an interval (a,b) - I took it as open because I'm assuming, infinity could be possible too.
Disregarding biases for round values and such things, it's very possible that not a single vote occurs twice.
Thus you have to choose, which values to ultimately pick.
If the resulting choices are entirely uniformly randomly distributed over the whole interval, there obviously is no answer, but this is unlikely anyway (and once infinity is involved, it's, in fact…

Whoa I didn't realize how long that was

Peter Tamaroff

@leo I'm trying to determine the order of the generalized quaternion group $\mathbb H_{n}$ defined as $\langle R,S\rangle$ where $$R=\begin{pmatrix}\omega & 0\\0&\omega^{-1}\end{pmatrix}$$ and $$S=\begin{pmatrix}0&-1\\1&0\end{pmatrix}$$

$ \omega$ is a primitive $2^n$ root of unity.

Note that $R^{2^n}=1$,$S^2=-1$

Moreover $RSR=S$

$SRS=-R^{-1}$

That is, $RSRS=SRSR=S^2=-1$

And $R^k\neq R^j$ when $j\neq k$ and $j,k<2^n$.

I'm thinking this suffices to reduce any string of $R,S,R^{-1},S^{-1}$

Charlie

@leo ¡Hola!!!

@jayesh .....

Karl's students

4:30 PM

@JasperLoy: Where are you?

Jayesh Badwaik

@Charlie .....

Charlie

Where is skullpatrol.... ?

Jayesh Badwaik

@Charlie you told him to leave yesterday. He is not coming back I think.

ehhh

κρανίοπεριπολία

Muahahaha

Charlie

@κρανίοπεριπολία >8-(

κρανίοπεριπολία

4:49 PM

@Charlie )8<

Charlie

@κρανίοπεριπολία what did you say that you removed???

user19161

@Karl'sstudents I am here.

Karl's students

@JasperLoy Oh you are here. :D

Charlie

Hi @jasper

user19161

Haha, so the penis questions were removed but not the suicide questions, haha!

Dominic Michaelis

4:53 PM

my flaggs were declined

user19161

I just think that in both cases, the asker is a troll.

user19161

In fact, it might even be the same person!

user19161

@Charlie Yes, your potato is baking. =)

Charlie

@JasperLoy really? Why?

Peter Tamaroff

I POSTED ON MAIN!

user19161

4:55 PM

@Charlie Not really.

user19161

@PeterTamaroff Yes, yes...

Charlie

@JasperLoy good, dear, good good

user19161

...

user19161

@PeterTamaroff I see that now you have no more accepted answers at 0...

Peter Tamaroff

@JasperLoy Good.

user19161

4:58 PM

@PeterTamaroff Hehe.

Charlie

@JasperLoy jaspy, I saw that you asked about me when I was away... You missed me, how cute :)

3

Dominic Michaelis

@jasper were your flaggs declined ?

user19161

@Charlie No, I just treat everyone the same.

Leong Lyn

@ Dominic hi i'm on the chat

user19161

@DominicMichaelis Hmm, I did not check, but probably, but it is OK.

Dominic Michaelis

5:02 PM

@LeongLyn hi

Jayesh Badwaik

Etiquette Guidelines | $\LaTeX$ support for chat

4

The previous message was not pinned by the owner. bad owner ;-)

Charlie

@JasperLoy ans you missed just the same :)

user19161

We need the great anon to pin.

user19161

Where is my god?

Jayesh Badwaik

He has forsaken you.

leo

5:06 PM

@charlie hi!

@Peter I think you are right

Peter Tamaroff

@leo Ah?

leo

The order of generalized quaternion group

Charlie

@leo como estas?

leo

@Charlie bien. Tú?

working in a take home exam

Peter Tamaroff

@leo Ah, OK.

Charlie

5:13 PM

@leo bien bien

Kasper

A question if I may, how does one get reputation points at chat.stackexchange.com ?

Dominic Michaelis

its the sum of the repuation of all of your se accounts

user19161

I just got some spam from a Russian dating site, hahaha!

Kasper

@DominicMichaelis hm.. as this user has 36 points on MSE but still 1 on chat stackexchange

user19161

They would not spam me if they know that I am only a banana!

Dominic Michaelis

5:25 PM

the points are a bit delayed

Jayesh Badwaik

@JasperLoy actually its the opposite, they spam only bananas

Cortizol

how to write residue sing like here: http://mathworld.wolfram.com/ResidueTheorem.html
for example, Res in z=1, put z=1 under Res... :)
thanks

user19161

@JayeshBadwaik LOL

Dominic Michaelis

@cortizol what are you trying to do ?

κρανίοπεριπολία

Can you make spam with bananas?

Banana spam.

Dominic Michaelis

5:29 PM

skell sounds like fruit salad for me

Cortizol

@DominicMichaelis To write Res z=1, put z=1 below Res, like on that link (bad English, sorry :))

@DominicMichaelis In TeX offcorse

Dominic Michaelis

ah ok $\operatorname{Res}_{z=1}$

wait i am confused $$\operatorname{Res}_{z=1}$$

ah ok take $$\underset{z=1}{\operatorname{Res}}$$

Cortizol

thank you

Dominic Michaelis

\underset{z=1}{\operatorname{Res}} in a math environment

user19161

That "help" in the title would do nothing for you other than making it less informative. — Gigili 7 mins ago

user19161

5:35 PM

I dislike such comments. What do they teach new users? Why not just edit the question directly?

Peter Tamaroff

@JasperLoy I'd just usually write "Please make the title more informative."

user19161

And @peter great edit there, that is the right way to educate new users...

Peter Tamaroff

@JasperLoy Where?

@JasperLoy Sarcasm?

user19161

@PeterTamaroff Same question. No, you are truly great!

Peter Tamaroff

@JasperLoy I'm not this guy!

user19161

5:37 PM

@PeterTamaroff That guy is not great. Only you are great to me.

Peter Tamaroff

I am determined to do all 128 exercises in Mariano's algebra book!

user19161

@PeterTamaroff That is a power of 2!

Peter Tamaroff

They are all quite awesome.

@JasperLoy Oh, that makes it even better.

user19161

Did not know he has a book.

user19161

But I can't read Spanish.

Peter Tamaroff

5:39 PM

@JasperLoy The book is called "Rings and it Categories of Representations". But I am just going through the chapter on Groups for the moment.

user19161

@PeterTamaroff Ah, I think you should just focus on your Jacobson for now...

user19161

The two volumes will last you to PhD level.

Peter Tamaroff

@JasperLoy But Jacobson has little exercises.

When I finish a few of these exercises I shall move on to Rings.

user19161

@PeterTamaroff Well, reading the book itself is a major exercise.

Peter Tamaroff

@JasperLoy Yeah, of course.

@JasperLoy What do you prefer ${\rm GL}(n,K)$ or ${\rm GL}_n(K)$?

Jayesh Badwaik

5:42 PM

I prefer the second one.

user19161

@PeterTamaroff Use whatever you like. I don't really use either very much.

Peter Tamaroff

@JasperLoy Well, I was asking you, not because I was hesitant.

Gigili

@JasperLoy What will a direct edit teach them?

Why don't you think more?

Peter Tamaroff

@Gigili Did no one complain you're advertising on MSE?

Dominic Michaelis

someone writing help in the title is hardly able to learn anything ...

Gigili

5:47 PM

@DominicMichaelis Quite right, but pointing out that it's no acceptable in a comment is much more helpful that editing the word out.

A 5 year old child would realize that.

κρανίοπεριπολία

I thought there was an age limit for this site?

Charlie

@κρανίοπεριπολία HAHAHAHAHA

κρανίοπεριπολία

2 mins ago, by Gigili

A 5 year old child would realize that.

Charlie

@κρανίοπεριπολία indeed

κρανίοπεριπολία

@Charlie HOHOHOHOHO

Dominic Michaelis

5:51 PM

look at the tags here

Gigili

@κρανίοπεριπολία Not all people obey rules.

Charlie

@κρανίοπεριπολία these are our evil laugh

user19161

And huhu is the new greeting, LOL

Charlie

@κρανίοπεριπολία SCHUCKULLY'S LAUGH

κρανίοπεριπολία

Mua HA HA HA

Charlie

5:56 PM

MWAHAHA };-)

@jasper you like penises? I hope you refer to your own }:)

user19161

Remember that body of question should be self-contained. Title should be concise yet descriptive summary of body. Question should be asked in interrogative and not imperative. Context should be included but thanks should be excluded.

Charlie

@JasperLoy thanks

user19161

@Charlie I like them all, but let's not talk about them anymore and attract unwanted attention from the flaggers.

Charlie

@JasperLoy lets not flag male genital

κρανίοπεριπολία

And the partridge should be in the pear tree ;-)

Dominic Michaelis

6:03 PM

well if it is big enough to get a flag ;)

2

user19161

@DominicMichaelis Flag not flagg.

Dominic Michaelis

oh right sry

Charlie

@DominicMichaelis HAHAHA

Cortizol

6:17 PM

how to write real and imaginary part $\Re$ and $\Im$, but with "e" and "m", but same form as $\Re$... I saw this in one book.

\mathfrak...

it's ok now

Charlie

@dominic.and how is your physics?

Jayesh Badwaik

6:42 PM

@anon please pin the LaTeX/etiquette message. :-)

Dominic Michaelis

@charlie i am a bit frustrated of the behaviour of my tutors

anon

@JayeshBadwaik I did that first thing after I came in the room

late on the uptake there

The Substitute

Hi. What does bold H mean in this context: $\partial D^4 = {(w,x,y,z\in H: w^2 +...+z^1=1}? Here $\partial D$ is depicted as the stereographic projection of two reference circles in the unit quaternions.

Peter Tamaroff

@TheSubstitute Quaternions?

anon

bold / blackboard bold H is commonly used to refer to the set of quaternions

The Substitute

6:53 PM

@anon, thanks. I had seen Q used as well, but I've also seen H for the upper half plane. Thanks.

anon

the problem with Q is that that is reserved for the rationals. H stands for Hamilton. Q8 is the quaternion group though.

The Substitute

Ah, that makes sense.

user19161

@anon Better late than never.

anon

@robjohn apparently the merge also moved my comment, unfortunately. oh well, I'll delete it.

robjohn

@anon I will be doing so as well

Cтарый Джон

7:03 PM

Hi all

anon

yo

user19161

@CтарыйДжон Hi Russian spy!

Cтарый Джон

@JasperLoy spy - nyet , russian - nyet :)

user19161

@anon Yo yo is a toy and Yo Yo Ma is a person.

Cтарый Джон

@JasperLoy a rather fine cellist, I believe

user19161

7:05 PM

@CтарыйДжон And you are a rather fine old man, I believe!

Cтарый Джон

@JasperLoy man, yes - old, yes - not sure about the rest :)

user19161

Guys, yesterday I was thinking that I might live till 99.

user19161

So I am making my life plans based on this magic number 99.

Cтарый Джон

@JasperLoy looking at my ancestors, I will be lucky to get to mid 80s - 99 would be excessive, I think

user19161

@CтарыйДжон Although sometimes, I really wish my life would end at 33. =)

Cтарый Джон

7:08 PM

@JasperLoy no point wishing for things like that!

κρανίοπεριπολία

Be careful for what you wish for.

Cтарый Джон

@κρανίοπεριπολία exactly!

user19161

My elementary school teacher died at 33.

Peter Tamaroff

@JasperLoy Cause?

user19161

She was a great person, but she went for a brain surgery and went into a coma.

user19161

7:17 PM

She is one of the most caring people I have ever met.

Peter Tamaroff

@JasperLoy Why did she undergo brain surgery?

user19161

There are not many people like her on this planet.

user19161

@PeterTamaroff Because of a tumour.

user19161

And she only just completed her doctorate in mathematics.

user19161

I met her a few weeks before she died.

user19161

7:18 PM

That meeting, she went to collect her photo which she had just taken.

user19161

That photo was used on her tombstone.

κρανίοπεριπολία

Life is a Path, Death is a Destination

user19161

Final Destination. I watched many of those...

user19161

@κρανίοπεριπολία I believe you have an extra "for" there.

κρανίοπεριπολία

You've chose the path less traveled.

user19161

7:25 PM

The way is narrow.

user19161

The road is long.

user19161

Life is difficult.

κρανίοπεριπολία

The choices are yours.

user19161

But the outcomes are not yours.

κρανίοπεριπολία

And only yours.

user19161

7:27 PM

I am now inspired to talk about willpower and destiny...

user19161

There is the eternal debate on free will and predestination...

Cтарый Джон

Must get ready to meet some friends for drinks - later folks

κρανίοπεριπολία

You can only try to change the things you can.

Peter Tamaroff

@JasperLoy Didn't know people use pics on tombstones.

κρανίοπεριπολία

@CтарыйДжон later

user19161

7:28 PM

This is what I currently believe from my limited understanding of the cosmos: there is free will and there is also predestination.

user19161

One makes his choices freely, but once that is done, the outcome is determined by the universe.

user19161

There is no contradiction.

user19161

This is the meaning of the phrase "One keeps doing his best until his destiny is revealed" in The Last Samurai.

Dominic Michaelis

capped and having 5995 reputation, i guess tomorrow i hit the 6k

btw why does this question have 4 close votes ?

user19161

@DominicMichaelis I perceived it as a question about the software and not the math.

Dominic Michaelis

7:43 PM

yeah me too, but in the faq it says that they welcome questions about software mathematicans use, and if not we should change the faq and burninate the tags

ablmf

I'm grading some assignments. Some students claimed that given a graph G with n vertices, we can find all simple cycles in polynomial time. I kind of dubious about this claim. What do you think.

Karl's students

@JasperLoy: Oh my ghost: data.stackexchange.com/tex/query/65683/top-investors

Transcript for

$Mathematics$ Mathematics