Mathematics - 2012-03-23 (page 3 of 3)

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8:02 PM

@hhh Good to know, good to know; thanks :-)

-5

Q: Data liberation in iPad?

I hate products that tries to jail users. Is there some policy about data liberation (something like with Google products here) with iPad? I have an iPad without 3G but I was considering a new iPad with 3G. But I have no interest to upgrade to a new iPad without proper data-liberation policies (o...

This is a common problem with many other so-called high-end products, even cyanogenmod where you need to parse all kind of obfuscated drivers if you really want to do something more serious with them. Everything is dxmn closed -- if you are perfectionist, you cannot do them the slightest better -- makes me always feel bad when I find bugs...

2

A: Linux Cell Phones?

Are they any good? My answer is about Nokias and Androids. I recommend you to wait with them until the problems fixed below. Poor Keyboards with Nokias but not with Androids, at least G1. Poor usability in both camps however will hinder your productivity The family, N8XX and N9XX, has ver...

Most of this marketing facade around Nokia, Android and Apple are just junk -- I wish there was something better :P ...I have stopped to waste time on them, perhaps some day.

@KannappanSampath Yo

Kannappan Sampath

Hi...

but running!

Feel free :P

@hhh What do you mean?

8:09 PM

...that I am going to run so I get damn out of my mind for a while and then back to math :)

@Ninefingers Hi, whatz up?

@Ninefingers do you know what "seen" means in this: seen 2m ago, talked 1d ago? It is on everybodies gravatars. Seen by who, is my question?

@hhh The point with that floor function is that the $2\pi/3(3\theta/2\pi - \lfloor 3\theta/2\pi\rfloor)$ starts off the same as $\theta$, until $\theta$ gets to $2\pi/3$, at which point it jumps back to zero.

Unless I've messed it up, of course.

user image

Mmm...

@Skullpatrol Last time they loaded / interacted with chat, I think.

talked is the last time the user said something into a chat window, somewhere.

@JonasTeuwen Is your hair? GREEN!!!

8:18 PM

Yes.

Can't you see?

@JonasTeuwen Along the top. The rest just looks dark brown.

@MattN Hi

Hullo.

@AsafKaragila Operator.

@Gigili 'Ello, how are you?

'Ello.

Ello.

8:26 PM

y Ello w

@Skullpatrol I'm fine, thank you.

@Skullpatrol Looks more orange than green to me. That, BTW is a much better photo than the one in Jonas's avatar.

@gigili Is you're name of Italian origin?

In what sense is it better? @David

@Skullpatrol No, I made it up. I doubt if such a word exists.

8:38 PM

Warmer skin tones, more balanced around the eyes, less of the "stressed out geek" look. All in all, a much more attractive photo.

In Italian, "gigli" means lilies, but I'm unaware of a word "gigili" in any language.

We call a baby in our language "gigili", as in What a cute baby, gigili migili.

Or Guguli maguli.

Whatever.

It's completely meaningless.

Interesting. In Bosnian, "cigoli migoli" means "all messed up".

@Gigili What language is that?

@Skullpatrol That's not the point.

|:(|

8:41 PM

Or maybe they spell it "cigili migili", I'd have to ask the resident expert. In any case, it's made up; not real words.

That's what I said.

No, I mean when Bosnians say "all messed up", it's not real words, really. Kind of like "higgledy piggledy" in English.

@MattN Why the long "face?"

@DavidWallace Are you saying that higgledy is not a real word? ;-)

@Skullpatrol That's a robjohn emoticon.

8:43 PM

Yes, and like neener neener.

@MattN It is?

My goodness, look what I found!

What a nice word, BTW.

@robjohn >:(

Ciguli Miguli is a 1952 Yugoslav political satire film directed by Branko Marjanović and written by Joža Horvat. It was meant to be the first satirical film of the post-World War II Yugoslav cinema, but its sharp criticism of bureaucracy was politically condemned by the authorities and the film was banned as "anti-socialist". Plot Ivan Ivanović, a party functionary, arrives in a provincial town as a temporary replacement for a cultural official. The newcomer is fanatically eager to reform the town's cultural life in accordance with socialist ideals. He abolishes all five music societies ...

8:46 PM

@robjohn No, apparently I got it wrong...

@Gigili What does "neener neener" mean?

@DavidWallace It is a childish taunt

@DavidWallace Such as in, "you can't catch me, neener, neener!"

No commas.

> A great way to annoy someone. Best if said while putting your thumb on your nose and waggling your fingers.

4 mins ago, by David Wallace

My goodness, look what I found!

Gigli () is a 2003 romantic comedy film written and directed by Martin Brest and starring Ben Affleck, Jennifer Lopez, Al Pacino, Christopher Walken, and Lainie Kazan. After a protracted battle between studio and director, a radically revised version of the original film was released. There was significant media attention and popular interest prior to its release, primarily because Affleck and Lopez, the film's stars, were romantically involved at the time. However, critical reception was extremely poor, and in the years since its release Gigli has frequently been cited as among the wor...

pictures Gigili with her thumb on her nose, waggling her fingers with faces drawn on them how come I've never heard this?

They've missed an 'i'.

8:49 PM

Write to the director!

I would think the producer would be more appropriate.

@DavidWallace Haha, thanks. Luckily I don't mind very much ;-)

Write to them all!

Hello World!

Hi

9:01 PM

First Java program blablabla, yes I know it.

@WillHunting Hi

@Skully - why did you remove the giraffe picture? It was cool. And educational (for me at least).

user19161

@Skullpatrol Hi! You like hanging out here don't you?

user19161

@JonasTeuwen Nice photo!

@DavidWallace Some people might get over sensitive about its educational value.

9:04 PM

Hah, when I saw that picture I was thinking, hmm, I'm actually not looking 18 anymore 8-).

@MattN Hi.

@AsafKaragila Hi.

What about "Operator"?

You asked what the O stood for.

@Skullpatrol People who are offended by giraffes?

9:06 PM

Oh.

@DavidWallace and anything else I do in here... like I said, selectively over sensitive. Note case in point above^

@DavidWallace, in short he's been trolling the chatroom for the past few months and now he cries that even he is trying to contribute to the chat in a meaningful way - people get angry at him.

@AsafKaragila Do you talk for EVERYONE

2

@Asaf - it's a chat room. It doesn't all have to be completely meaningful.

user19161

@AsafKaragila I don't think he is a troll in a bad way. I think this room need not be so serious all the time.

9:11 PM

@Skullpatrol No. I talk about myself, and about the rather starred comments by several people that asked you to be less trolling. I don't know, but I can't be accounted for all those stars.

This chatroom is hardly ever serious. Not all trolling is enjoyable.

user19161

I thought mathematicians had a great sense of humour, maybe I was wrong.

2

I don't really mind trolling. As long as it is entertaining. And bad trolls are not entertaining. Keeps me awake at night :(.

@Skully I don't think Asaf talks for everyone. This is a place to come and chat.

@WillHunting No, mathematicians have a peculiar sense of humor.

I hate weekends.

9:12 PM

At the end of the day, if someone doesn't like a comment, they can just ignore it.

@Gigili Why?

Gigili - why?

@DavidWallace Of course I don't. I don't talk for you, and I don't talk for Will. I obviously don't talk for Skulloftroll here as well.

That's three counterexamples for "EVERYONE" right there.

If Skully's comments were actually offensive (racist, sexist or whatever), it would be a different story. But basically, if they're just irrelevant and slightly annoying, well who really cares?

Because I am bored to death.

9:15 PM

I know that I do talk for myself, and I do talk for the several different people which starred the comment of Skullpatrol when he was "Oh lord, if several people star this comment I am leaving forever". I also know that in private conversations several people have expressed distraught about his presence at times.

@Gigili no hobbies?

@robjohn Uhum. =\

@DavidWallace Ever had someone stand by you and say "David" in a monotonic voice for half an hour? That is not sexist, racist, or otherwise offensive. However if you don't want to punch that person in through the back of his skull then you must be deaf to begin with.

If someone did that, I would walk away.

I've found an interesting feature on all my browser windows. It's this little X, on a red background, up in the top right corner.

2

Then walk away.

9:18 PM

I'm not sufficiently upset yet. And there are people here whom I'm actually enjoying talking to.

→ 1 message moved to The Bin

@DavidWallace See? I don't see why I should give up the entire room just because of one pesky little troll. I do see the reason, however, to defend my stand for disliking him.

@DavidWallace I'd make them walk away instead.

2

Especially when this stand is presented as irrationally over sensitive.

@AsafKaragila New feature?

@MattN Old feature which I have finally found how to use.

9:20 PM

@Gigili how?

@AsafKaragila I assume only the room owner has the power.

@MattN Also moderators... :-P

Yeah, I don't see how I am being selective. If it were up to me you would have been removed from the chatroom altogether, not just parts of what you say.

@Gigili It seems to me that in most situations, walking away oneself is easier than trying to persuade someone else to.

@Asaf - nice edit; I was about to rip into you for what you said the first time.

@DavidWallace Seeing how I am the Owner of the chatroom, might be nearly meaningless - and as Skullpatrol would say I am completely power tripping here - but it still means that it is not I who should walk away.

@DavidWallace That's what I'd like to do but that little X up in the top right corner is my best friend. I'd throw something at the person but I never have done it. I have no choice there.

@DavidWallace Painfully true.

9:24 PM

There's also an "ignore" feature that Robust 0 uses on me!

I ignored him for a while.

user19161

@DavidWallace Robusto?

That's the most useless feature ever.

I do believe that when someone which supposes to maintain the room ignores a person then that person is better removed from the room altogether. Either way, now that I can effectively remove his posts from the main room I see no need to ignore him. If he crosses a line, his posts will be removed.

user19161

I see that @jonas has changed his avatar into the very good-looking one!

9:26 PM

@Gigili Is it? I don't really know how it works; but it amuses me that Robust 0 chose it as a way of dealing with me.

Yes :-).

Jonas, Will is lying. Your avatar was better before. With the stars and all that.

Yeah, I know.

@DavidWallace Just ignore someone in the middle of a semi-war and see all @THEDAMNPERSON messages getting on your nerves. You ignored them and other users start to get attracted by that person at the same time. It's exactly how it works.

user19161

@AsafKaragila Nope, I never lie.

9:29 PM

@WillHunting You lied just there.

I don't care.

@Gigili - Robust 0's actions cause other people to get attracted by me? That's a pretty cool feature!

@DavidWallace Umm, that's how you interpret it.

user19161

@AsafKaragila But I do lie down...

@WillHunting TMI.

user19161

9:33 PM

@AsafKaragila Huh, don't you lie down to sleep?

@WillHunting I do, but I don't want to know about what you do when you lie down. That's between you, your right hand and your pillow.

@AsafKaragila Could you please choose which of these 66 definitions you think fits my supposed "trolling" and then I will try to not do it in the future.

@DavidWallace Well that is totally different what floor -function usually mean! It usually mean that to get back to the nearest integer...very well there must be some flag to handle this. Actually, is Modulo what you are looking here instead of the floor -function? Start again from 0 when $\frac{c\pi}{b}$ -some-condition?

@Skullpatrol No, and that is the sad part. The only way you can stop being a troll is if you take a few years to grow up. That's just how life is in these parts of the internet. I should know.

@hhh Look at the equation; I subtracted off the floor part!

9:42 PM

hi folks. given the position of a particle in parameterized form (x(t), y(t)), the distance the particle travels from t=a to t=b is the integral of sqrt(x^2+y^2)dt? Or is it the integral of sqrt((x')2+(y')^2)dt? If the latter, why do you have to take the derivative first when you have position functions and you're calculating distance?

@AsafKaragila Hmm... interesting point of view.

@hhh $x - \lfloor x \rfloor$ is always in [0,1).

@Jeff it is the latter. The derivative is so that you measure the small increments of distance correctly.

$\mathrm{d}s^2=\mathrm{d}x^2+\mathrm{d}y^2$

@robjohn if you have position equation, $f(x)$, then the distance between two points is the distance equation. $\sqrt(x^2+y^2)$. yes?

@Jeff The straight line distance, yes; but not the distance along the curve.

9:46 PM

Commonly, $x - \lfloor x \rfloor \in [0,1)$, your floor function has different definition to this!

Look R does not even seem to support your floor -function, perhaps rewriting this in modulo?

@robjohn ok. right. but then you take really small increments of those distances. so you're still not working with the derivative. you still have that the hypotenuse of the small distance is $\sqrt(x^2+y^2)$. How do you get to using the derivative?

@Jeff Travelling around the unit circle, you can travel from $(1,0)$ around the circle to $(1,0)$, travelling $2\pi$, but ending a distance of $0$ from where we started.

@hhh WTF do you mean "has different definition". This is what "floor" always means.

@Jeff by taking limits, as is always the case when using derivatives.

@DavidWallace Sorry misread, yes sure :P ...stupid misreading...read and thought it differently, yes that is correct.

9:50 PM

Did I bugger up the LaTeX? I don't have MathJax switched on, and I frequently do something dumb like missing a backslash.

@DavidWallace why no MathJax?

$\lim_{t \rightarrow 0}\sqrt(x(t)^2+y(t)^2)dt$

I keep losing the link to it. And since I can read it most of the time, it's just not worth the trouble.

@DavidWallace Yes but now we have radians with that condition $\left(\frac{3\theta}{2\pi}-\left\lfloor\frac{3\theta}{2\pi}\right\rfloor\right)\in[0,1)$, $1 \text{ rad } <\frac{2\pi}{3}$ -- how does it work now?

@Jeff the limit as the maximum size of the approximation of the curve tends to $0$

9:52 PM

@DavidWallace What? How do you lose a bookmarked link?

@Jeff what is that?

@robjohn a misunderstanding? :D

OK, start at $\theta = 0$. Run around to $2\pi/3$, and the expression in brackets is just $\theta$. But as soon as you get to $2\pi/3$, it becomes $\theta - 2\pi/3$, and you start running along the second side of the triangle.

2

@Gigili Aha! I just found it.

I put it in a folder and forgot which one.

Umm, I when I said "expression in brackets", I meant with the factor of $2\pi/3$ included. Otherwise what I said makes no sense.

@AsafKaragila strongly disagree.

@anon Yo dude whatz up?

took my grandpa to the hospital. they put a camera down into his lungs and took pictures. that's pretty much my day.

9:59 PM

@tb Hi

hi

Hi Teddy.

Hi Matt peeks out of the trunk

: )

Is tb intended to stand for teddy bear? When I see it, I think of tuberculosis.

10:00 PM

You can come out. I have recovered from feeling miserable.

'Ello @tb.

I think I now have a full proof of the $z^n$ thing.

@DavidWallace Can teddy bears get tuberculosis? In which case it would be a tb with tb.

Just needed to fill in a ton of missing details in the proof linked to by Zhen.

Well, I still think that one is the best... In fact, it's a piece of covering theory.

10:01 PM

Well ton might be a slight exaggeration. But it needs covering spaces and unique lifting property. I didn't know either before today.

I hate the details. Lord how I wish I were a mathematician in the 15th century. No details, no one cared about them.

Sorry are we speaking of the same formula?

$$\left(\frac{3\theta}{2\pi}-\left\lfloor\frac{3\theta}{2\pi}\right\rfloor\right)\in[0,1)$$

Covering spaces are nice.

Now that I know just how much stuff I didn't know that is needed to do that proof I'm not feeling so bad anymore.

I ran into this teacher recently and mentioned this quiz problem. She said she thought my son had written "8" and didn't know that a sideways "8" means infinity. I don't even

10:03 PM

@Jeff You need to partition the curve into pieces at points $\{(x_i,y_i)\}$ so that $|(x_{i+1}-x_i,y_{i+1}-y_i)|<\epsilon$ and so that for almost all $i$, $\left|\frac{(x_{i+1}-x_i,y_{i+1}-y_i)}{|(x_{i+1}-x_i,y_{i+1}-y_i)|}-\frac{(x_i-x_{i-1},y_i-y_{i-1})}{|(x_ix_{i-1},y_i-y_{i-1})|}\right|<\epsilon$

Locking you in the trunk for half a day for making me feel bad for a day seems like an adequate punishment. Now we're even.

@hhh Yeah, now multiply the whole lot by $2\pi/3$ and it'll be in $[0,2\pi/3)$.

@anon In what sort of quiz would infinity be a correct answer?

@robjohn where $x_{i+1}=x(t+h)$? right?

56

Q: How many sides does a circle have?

My son is in 2nd grade. His math teacher gave the class a quiz, and one question was this: If a triangle has 3 sides, and a rectangle has 4 sides, how many sides does a circle have? My first reaction was "0" or "undefined". But my son wrote "$\infty$" which I think is a reasonable answer. ...

geometry education circle

@tb You could've told me that two days ago... that could've saved me a lot of pain.

10:05 PM

You don't need to spell that stuff out, though. I think the proof I outlined does not have many details missing.

@Jeff Depending on how the points are being parametrized, $x_i=x(i/n)$ where there are $n+1$ points in the partition

I'm going to spell it out since I still don't understand the proof you outlined.

assuming your curve is parametrized from $0$ to $1$.

I have to go afk for a while. bbl

The only thing you need to know is that closed subgroups of $\mathbb{R}$ are cyclic if they aren't $\mathbb{R}$ or $0$. That's straightforward to prove: you have a smallest positive elements and that one generates.

Will post it as an answer to my question.

10:07 PM

@robjohn so then how do you write the limit equation for that?

So

$$\frac{2\pi}{3}\left(\frac{3\theta}{2\pi}-\left\lfloor\frac{3\theta}{2\pi}\right\rfloor\right)-\frac{\pi}{3}\in\left[\frac{-\pi}{3},\frac{\pi}{3}\right)$$

@DavidWallace: where do we need this now? It is inside $\cos(...)$, thinking.

(by the Archimedean property).

@robjohn yes, 0 to 1.

@tb Never heard of.

@robjohn oh. ok. i'll finish this up myself. thanks

10:08 PM

@Jeff The Riemann sums for the integral...

@hhh Right. Now take the cosine.

I type an answer, OP deletes his thread. minutes later thread is restored, two people post the same answer. flip table

@anon So post your answer again, and downvote the other two so that yours comes to the top.

@robjohn yeah. i'm trying to understand the why of using the derivatives in $\sqrt{x'^2+y'^2}$.

it's an elementary DE question, every answer is going to be the same

10:10 PM

@anon True story.

@Jeff they kind of undo the integration that you're about to do.

And they will comment "Mind to explain why?"... Geee, I'll kill you if you say it.

@Gigili which anon can then ignore. Everyone else does.

In fact he/she should tell us which question it is, so we can all go there and apply the same downvotes, just as a show of solidarity for anon.

@DavidWallace Not me.

Unless one of the answers is mine, in which case we should all downvote anon.

10:11 PM

@Jeff $\int_0^1|\gamma'(t)|\,\mathrm{d}t = \lim\limits_{n\to\infty}\sum_{k=0}^n|\gamma'(k/n)|\frac1n= \lim\limits_{n\to\infty}\sum_{k=0}^n|\gamma((k+1)/n)-\gamma(k/n)|$

@Jeff: Does $\sum (t_{i+1}-t_i)\cdot \frac{\|\vec{x}(t_{i+1}-\vec{x}(t_i)\|}{t_{i+1}-t_i}$ help?

@DavidWallace XD

@Gigili OK, so in the "mind to explain why" you write "because your answer is just repeating what anon has already said".

the question was deleted before I got a chance to submit. they ended up being able to answer before me after the restoration.

Sorry but I doubt I can be that cruel.

10:13 PM

@Jeff think on that while I am gone.

@anon maybe. i'll get back to you. i want to look at robjohn's

how did he make a link to his chat message?

you can find your own message id with the permalink

@anon like this

@tb How's your head?

@MattN If $0 \lt x \lt y$ then there is $n \in \mathbb{N}$ such that $nx \gt y$.

@MattN much better, thanks.

Does this mean it's ok again?

10:18 PM

6 mins ago, by anon

@Jeff: Does $\sum (t_{i+1}-t_i)\cdot \frac{\|\vec{x}(t_{i+1}-\vec{x}(t_i)\|}{t_{i+1}-t_i}$ help?

@MattN not perfect but much better.

@anon Yes, but you can say it anyway. What's the worst they can do to you?

it's a basic question, my care has come and gone

@anon well, to the right of the dot is the difference equation

@anon I'm not defending the teachers answer, but you can have a one sided argument if you talk in circles, therefore a circle has one side ;-P

10:21 PM

it's the magnitude of the difference from 1 point to the next, divided by the time difference

@skull lol

@skull I was talking about the differential equation question

@DavidWallace $\cos(x)\in\left[-0.5,1\right]\text{ where } x\in \left[\frac{-\pi}{3},\frac{\pi}{3}\right]$. But what does that mean in our case here?

@anon but how did you get that from the distance equation $\sqrt{x^2+y^2}$?

Sure, the particular triangle that I drew is 1 away from the origin at the vertices, and 1/2 away from the origin at the midpoints of the sides.

2

@Jeff: $$\frac{\|\vec{x}(t_{i+1})-\vec{x}(t_i)\|}{t_{i+1}-t_i}= \|\vec{x}'(t_i)+\mathcal{O}(t_{i+1}-t_i)\| =\sqrt{\dot{x}^2+\dot{y}^2}$$

10:24 PM

@Jeff, why don't you do a few worked examples with different curves, and you'll see why it makes sense.

$\boxed{\;\,\stackrel{{\diagdown\;\;\;\;\;\diagup}}{\stackrel{\phantom{\int_{a}}‌}{\color{gray}{\huge\frown}}}\;\,}$

Japanese Mean Square

Someone looks bored...

But hey -- I know what you could do!

sleep?

@david i have. i know the how. i have a tutoring student who got this question wrong and asks me why i'm using the derivative when it seems like it s/b $\int{\sqrt{x^2+y^2}}dt$ :)

10:27 PM

Yes that as well (I'm about to force myself into bed, too).

I have actually done some work on the Whitehead thing. Huzzah.

@AsafKaragila Here's a carrot. feeds Asaf a carrot and pats him on the head

I think I will finish the proof that $A$ is a $W$-group if and only if $\operatorname{Ext}(A,\mathbb Z)=0$.

@Jeff: The easiest way to see that must be wrong is that it varies with affine transformations, while arclength does not.

@Jeff OK, I understand now. I need to sketch this on paper or a whiteboard to explain it to you. I think I've reached the limit of the medium.

10:28 PM

@MattN I am not a horse. Don't feed me carrots. Instead feed me steaks.

I prefer sirloin, medium to medium rare.

@DavidWallace in other words, given x,y in terms of t (x(t)=e^t, y(t)=e^t sin(t))

@david oh. ok. didn't see your last response before my most recent

Good night. I'm going to sleep.

heya

Good night, Matt

Don't stay up all night.

10:31 PM

@MattN I will try. Thanks!

@tb : )

@MattN I just noticed :)

Back to the Texmaker for me.

hi?

heya

10:33 PM

This might seem weird but I recently saw the question about how many sides a circle has. It seems like quite a peculiar thing to ask.

Because most primary school teachers don't have a mathematical education.

One of them tried to make me divide something by zero once.

I would say it is more a question about definition.s

(Is a circle a polygon with infinite many sides) or is it a own shape.

A polygon, by definition, has finitely many sides.

Eg how you would define what a side is, and how you would define what a circle is.

I guess we say things like "on the other side of the world", without imagining that there are sides of the world that are flat or straight.

3

10:37 PM

This might again sound silly, but what is a side then ?

Closed - general reference.

Whoops, I'm not @RegDwight, I mean, in the geometrical sense, it's a line segment.

But in everyday English, it has many other meanings.

I think the ambiguity of the question is well exposed in JDH's answer.

Sure. I would answer 0. If I had no mathematical training, I would probably answer 1. I can understand why somebody might answer infinity.

Oh well! Pie for everybody.

@JonasTeuwen Did you see my drawing?

10:42 PM

I think the serial star awarder has struck again.

@N3buchadnezzar No.

If I had no mathematical training, I would probably not bother answering the question. Instead I would drink beer and pick up chicks,

@JonasTeuwen Yesterday, a helicopter.

Or I would answer 2, an inside and an outside.

@N3buchadnezzar Unless you were in a quiz situation with an ill-informed teacher

@N3buchadnezzar Mmmm.

@DavidWallace I still think the beer and pick up chicks is a good idea, even during a quiz.

Circular arguments when discussing definitions of circles, yay!

10:59 PM

@N3buchadnezzar Show me.

Show you what? My drawing?

Yes.

11:14 PM

@tb I only recently learned about \boxed, so my attempt was not boxed, but I did one a while ago :-)

$\boxed{\stackrel{\stackrel{\hskip{1pt}\large\diagdown\hskip{6pt}\diagup} {\huge\bullet\hskip{7pt}\huge\bullet}} {\huge\frown}}$

I need to adjust some whitespace...

$\boxed{\stackrel{\stackrel{\hskip{1pt}\large\diagdown\hskip{6pt}\diagup} {\huge\bullet\hskip{7pt}\huge\bullet}} {\huge_\phantom{\small }\frown_\phantom{\small }}}$

$\boxed{\stackrel{\stackrel{\hskip{1pt}\large\diagdown\hskip{6pt}\diagup} {\huge\bullet\hskip{7pt}\huge\bullet}} {\huge_\phantom{\scriptsize }\frown_\phantom{\scriptsize }}}$

Hah. This is good.

$\boxed{\stackrel{\stackrel{\hskip{1pt}\large\diagdown\hskip{6pt}\diagup} {\huge\bullet\hskip{7pt}\huge\bullet}} {\hskip{-2pt}\huge_\phantom{\tiny }\frown_\phantom{\tiny }}}$

@robjohn You can sign your messages with that.

I don't see why not :-)

user image

11:28 PM

@N3buchadnezzar Wow. Art.

You should probably read the chat for the helicopter part.

I convinced skullpatrol that in Norway we tend to use helicopters instead of x`es. Since we do not tend to use those letters anyway.

I guess that brute force computation was not what got the votes on this problem. Davide Giraudo posted after and got 2 votes, so it is not a matter of being too late.

However, I do like the Cayley-Hamilton answer, but that was already given. :-)

Anyone familiar with linear algebra and Geogebra?

I will annihilate your matrix.

I want to be able to rotate a box in x, y and z direction

I was thinking of making some cosine and sine matricies, along with a R3 to R2 linear transformation, but I am a bit unsure about the details

11:38 PM

@N3buchadnezzar I know that someone was using Geogebra here a while back. search the transcript

I was? I didn't get it.

user19161

@N3buchadnezzar Nice!

I may be remembering Srivatsan.

2

It is a bit hard though

Perhaps it is best for me to search google

But if we forget geogebra for a minute

Calculating the points and rotating them according to theta and phi should be possible yes?

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