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11:12
Good day
Do you know how to obtain such representation for Hausdorff distance? $d(X,Y) = \max\limits_{\|l\| \leqslant 1} | c(l \mid X) - c(l \mid Y) |$, where $c$ is a support function
11:28
@Nimza: dunno, sorry
Hi @Ilya!
Ave @J.M.
@JM have you tried Limbo?
@Ilya The game, or the line you try to dance under ?
@Ilya I don't think I've even heard of it until now...
@JM i just remembered you are from waterloo as well.
11:31
@N3buchadnezzar Well, the second one, I am an expert...
@N3buchadnezzar the game
@Eugene Huh? No I am not...
@JM and about Braid?
@JM should be quite cold for you there :)
@Ilya Not that one, also. I'm a bit out of the loop...
@Ilya Not really, the temperature was 34 °C last I checked...
@JM yikes! it was j.d. my mistake.
11:34
@JM in waterloo?
J.D was your mistake? When did you make it?
Hola, BTW.
@Ilya No, here.
@Gigili Hi!
@Gigili i thought j.m. also went to waterloo. he doesn't.
@Gigili WTB, aloH
@Eugene So you've finished reading Dudley, I gather...
@Eugene (FWIW I'm not a mathematician either. :) )
11:37
@JM Huh, I guessed that must be the case.
@JM no. i didn't read dudley. i'm just curious about how to tell a genuine paper from a fake. it's hard to read through it and figure out why it wrong sometimes.
@Gigili How so?
@JM So why you love mathematica so much very uh?
@Eugene But you've at least seen Aaronson's take on the matter?
@Gigili It's a nice hobby.
@JM yup.
11:38
@Ilya ?yadot uoy era woH
Long time no see.
@JM those are the glaring cranks though...
@JM There are nicer hobbies if you ask me.
@Gigili dnuora delzzup
@Gigili Sure, I do some of them, but this is one hobby I can do sitting down...
@Ilya ¿ǝsɹǝʌǝɹ uı sƃuıɥʇ ƃuıʇıɹʍ ǝןdoǝd ǝɹɐ ʎɥʍ
@JM ¿Spahish?
11:42
@Ilya Not really.
@JM Because they are awesome like that?
@Gigili ping
@Ilya ereh emaS.
@Ilya I flagged you. Enjoy it.
@Ilya hop
@Gigili ah, a little liar. how could you? you're the kindest
who likes Shakira, hands up!
@Gigili btw, where is our little skulltroll friend?
Who, or what, is Shakira?
11:46
leaves
@OldJohn it's a cocktail with Colombian rhum. That sings and dances
@Ilya What the hell? Why you ask me?
@Gigili you visited this chat more often then me for some last time
@Ilya You're completely mistaken about me, it's my first time here.
@Gigili oh sorry. I mixed you up with whiskey. Whiskey is the one whom I need to ask.
11:50
I stir you up.
I made you up.
Pu uoy edam I!
my Turkish friend has told me that it sounds Turkish
Who sounds Turkish?
Pu uoy
Sie seniôr?
12:05
if $A, Q~$ and $~Q^T$ are matrices, does $Q^T A Q = Q^T A^T Q$ imply that $A = A^T$?
@Jaydon $Q = 0$
in general, if $Q$ is invertible - you know what to do. If not, then $A$ and $A^T$ can differ on the null space of $Q$
12:20
If you'll excuse me for the amount of rep you'll probably lose. Which is quite haha.
Was that remark directed at anyone in particular?
Wow @MattN you have been loading Math.SE with a lot of commutative algebra questions!
Certainly not, it was directed at the ones who answered my questions.
@Gigili which?
All of them.
12:32
@Gigili are you also getting deleted?
@Ilya: Does that only hold true if $Q^T Q = I$?
@JaydonZhao no :) just if $Q$ is invertible
or if $A$ is of less dimension, when $Q$ is of a full rank
@Ilya: Shouldn't $Q^T$ also be invertible?
that's equivalent: they have the same determinant
@Ilya: how does that imply that it's invertible? D: sorry
12:45
A square matrix is invertible iff its determinant isn't 0.
Or, another way, $(Q^T)^{-1} = (Q^{-1})^{T}$
@Eugene Probably so.
Or maybe not.
I'll kick the habit for sure.
13:01
@Gigili wow. drastic measure.
@David: thanks, I completely overlooked that property =="
@Elya: thanks for your help too :)
@Ilya*
you're welcome
are determinants defined for non-square matrices?
13:24
hey all i have a question of coordinate geometry here math.stackexchange.com/questions/157296/… for which i need a help
can anyone help me please?
13:54
@meg_1997 You don't have to accept an answer when it doesn't answer your question.
Your acceptance rate was a bit low.
is 60% ok ?
It is indeed.
hurray!!!:P
ok fine will you see my question?
Sure.
@meg_1997 OK, I didn't understand it quite well to draw the picture, but this might help you to get an idea. I'll be back later and will answer your question if I come up with a solution.
14:09
Ok :)
if $U_1, U_2$ are two $n \times x$ row-echelon matrices, is proving that $U_1 U_2$ is invertible if and only if $U_1$ and $U_2$ are both invertible, a trivial proof? (if we can't use the fact that $det(A)det(B) = det(AB)$.)
$n \times n$
Shakira Shakira!
@JaydonZhao $U_2$ has to be $x \times n$ for the multiplication to work...
sorry that was a typo D: I meant $n \times n$
@N3buchadnezzar Why the sudden interest in belly-dancing pop singers?
14:15
@JM I find belly-dancing more interesting than trivial proofs.
That is certainly a defensible argument... :)
Trivial proofs often lie, hips dont ;)
"N3b likes hips and he cannot lie."
@JM Shakira!
14:32
@N3buchadnezzar ...I don't bother
@Gigili: c'mon, what are you doing?
Staring in awe at the awesome hips
When i need to calculate $\vec{a} - \vec{b}$ and I have the coordinates, it is just straight plug and chug right? Been long since I have done this.
yes
I remember that when making a vector from A to B, one had to do it like \vec{AB} = B - A
so
14:43
how do I draw sketches in $R^4$...
@JaydonZhao what kind of sketch?
@JaydonZhao hardly :) you should be time-independent to see the whole picture
If you would like to go for a dimension between $5$ and $10$ you should be also smaller than quark to draw sketches
life is hard, oh yeah...
Asking students to draw things in R4 is the same as saying "whats up?" to creatures living in R2
"draw a sketch in $R^n$ and set $n=4$..."
no idea how to typeset column vectors in LaTeX
hm..
14:48
@JaydonZhao I do!
$[1,2,2]^\top$
$[1,2,3]^T$
@JM this reminds me of that old joke
an engineer attends a talk about a mathematician on $\Bbb{R}^{15}$.
he is so impressed with the mathematician's understanding of 15 dimensional space
so after the talk he asks the mathematician, "how do you think of 15-dimensional space that you understand it so well?"
the mathematician replies, "that's easy. first i think of $\Bbb{R}^n$, then i set $n = 15$.
Soup ?
If you cant say it with analysis, try flowers.
@Eugene Yes, that's the gag I was alluding to. :)
14:58
$S = \{\mathbf{x}: \mathbf{x} = \lambda_1 [2, 1, -2, 2 ]^T + \lambda_2 [4, -2, 3, -1]^T$ for $0 \leq \lambda_1 \leq 6~$, $0 \leq \lambda_1 \leq \lambda_2\}$
@JM i figured consider the similarity.
Is it called an infliction point where the graph is shaped as a UU ?
render
Eg $r = 1 + \cos \theta$
@N3buchadnezzar The inflection is the point in between the dimple and the extreme...
15:01
@N3buchadnezzar doesn't it look like $\infty$?
I was just trying to classify the different types of cases when f''(x)=0
I was thinking we have the case where the graph goes from convex to concave, the opposite case, and the third where it stays convex or concave through the point where f''(x)=0. Then I tried coming up with cases for the latter one. And $r = 1 + \cos \theta$ sprung to mind.
Can anyone offer some insight if you have the time? math.stackexchange.com/questions/157390/…
try mathoverflow
what is wrong with math stackexchange?
I was kidding :P
15:09
@AgainstASicilian i get the feeling this was asked yesterday
@JaydonZhao bad, bad boy :(
@JaydonZhao bad joke.
@N3buchadnezzar $x^6$ is better. In your case, btw, you still have a change of convexity
@DylanMoreland J.M. cast the vote to undelete.
@Eugene ...and you got a good answer from Willie.
15:11
@JM indeed.
i think mixedmath had some good pointers as well.
@Eugene does you last time start with "One" and end with "gin"?
@Ilya i'm confused.
@Ilya ...and a "more" somewhere in the middle.
OK, OK. This is just what the hell.
How in the world does that answer answers the question @meg1997?
I think the answer is "the rest must be easy".
15:14
@Gigili POK, POK.
I can answer over a million questions like that.
I don't understand, what's wrong with Math Stackexchange / Math Overflow?
@Gigili Calm. What are you talking about?
Should I go ask there?
@AgainstASicilian there where?
15:15
@AgainstASicilian No, not for this case.
(at least, not yet.)
@JM Why so?
The answerer just repeated what was given a more mathematical way and the rest must be easy ...
all my questions asked on overflow were closed :( I think they hate me J.M.
@AgainstASicilian If you're going to be asking a group of professional mathematicians, you'd do well to show initial effort first. Asking in this place before there counts as "initial effort".
15:16
@Eugene Good timing. See this.
@JaydonZhao Well, are your questions, to use their words, "of interest to research mathematicians"?
@Gigili it's not a "more mathematical" way
@JaydonZhao It isn't hate; just a desire to keep things clean. Don't take closures personally. If you think you can improve a closed question so that it is something better, edit it, and make a petition on their meta site.
Mochizuki is extremely legit, though.
@Ilya I know, it's the WTH way.
15:19
@DylanMoreland oh my.
@Gigili there is already 1 downvote, btw
And @meg1997 accepted it.
@Ilya I wonder if hip movements could be described by ellipsis, what do yo think ?
My questions on avreage obtains 7-8 upvotes! Thanks to me not posting very many questions.
@N3buchadnezzar The hip movements will definitely involve an inflexion point...
@N3buchadnezzar Ilya's thoughts: Beyonce, Beyonce. Shakira, Shakira
@Gigili in which universe?
15:21
@DylanMoreland this isn't the first one though.
@Ilya It must be Beyonce, Shakira, Beyonce, Shakira ... I believe.
@Ilya Emm, puts on her glasses It was accepted a minute ago.
i knew someone asked about t(n^2) here yesterday
@JM does a grilled bagel have inflection points?
this is starting to smell like homework
@robjohn i was apologizing for interrupting you yesterday over something trivial
@Eugene You mean your question that has been undeleted, or something else?
15:27
@robjohn depends on the bagel; I've seen weirdly-shaped ones a while back...
@robjohn yes the question that has been undeleted.
@JM I was referring to your grilled bagel :-)
@Eugene It was not trivial. You can't undelete yet, so we did it for you.
@robjohn thanks for your help then. i appreciate it
My long lost tooth seems to have been reunited with me.
@robjohn Oh, my last Gravatar? More like inflection lines, actually...
15:35
@JM Ah, I refreshed and see that you have a new gravatar :-)
@JM Your new one looks a bit washed out. Is that intentional?
@Eugene no problem. you're welcome
@Eugene No, not homework
@robjohn Yes, I was going for dull metal.
@Gigili: now's your chance...
@AgainstASicilian just coincidentally have the same question as this guy?
would seem so
@Gigili Tooth fairy reject?
15:42
@AgainstASicilian well like i answer him yesterday finding an exact answer to this is very hard and approximating really about the best you can do if you don't want to spend the time computing.
@AgainstASicilian may i ask what motivated this question?
@JM Indeed.
@robjohn It's a miracle!
@robjohn Could you help us with this problem?
@Gigili hang on...
@Gigili i want the user to tell how exactly he got those co ordinates
@meg_1997 I don't think he's going to tell you. He didn't really solve the problem.
15:58
@Gigili thought he really got those coordinates as i had observed that the x coordinate of vertex C is twice the x coordinate of vertex A and his answer was exactly this way so i accepted his answer and thought that he might explain it later on ....
@meg_1997 But the coordinates are given in the problem! He might explain, I don't know.
@Gigili Ya but only of vertex B which is the origin we don't know the coordinates of vertex A and C
if $A, B, AB$ are matrices can $(AB)^{-1}$ only exist if $A^{-1}$ and $B^{-1}$ exist? (since $(AB)^{-1} = B^{-1}A^{-1}$)
@meg_1997 I see, you meant vertices $A$ and $C$ in your comment.
16:06
@JaydonZhao square matrices?
@Ilya Yes, the OP unaccepted it.
@JaydonZhao: I think yes. Again, we can use the stuff with determinants
@Gigili oops typo!ya meant vertex A and C
hi ...
For constant coefficient second order DE, y''+ay'+by=0, are we guessing it will have solution of the form e^kt ,,, t being independent variable??
16:15
@experimentX a linear combination of exponentials, yes.
@Gigili Sorry to be away for a while. I had to talk to my boss. Have you figured that out yet?
isn't there another way of doing like first order DE?? ... i mean for general cases for constant coefficients??
@robjohn No problem at all. Unfortunately not.
@experimentX You know how to use the characteristic equation, no?
@Gigili what are we allowed to use? geometry, trig?
16:18
yeah i know ... still some confusion remains ... i would like to clear that ...
The angle at $A$ is $2\arcsin(1/3)$
@robjohn I guess so.
i was just wondering if it was like guessing the solution before hand or ... there is some theorem that says it has solution of this type
@experimentX the solution for a constant-coefficient case is always a linear combination of exponentials. (Some refinement is needed for the case of the characteristic polynomial having multiple roots, though.)
@Gigili okay, we can avoid trig, per se, but use the geometric equivalent
16:20
yeah i studied that ... thank you @JM
Hey ho
Is there a possibility to see the most rated question (answer) on MO?
@robjohn Aha, okay.
Or a question about batman is the most rated?
That, or $$\frac 10$$ ...
i see codes instead of latex .... in this chat ... is there something i've to do??
16:28
@experimentX See the first starred message on the right panel.
oh .. thanks .. ll do that
it's not possible for the chat system to support LaTeX by default?
@JaydonZhao No, which is why robjohn came up with that device.
ah, so it will never be implemented?
@JaydonZhao Not in the near future.
16:48
@JM what should i do after copying?? that script??
@experimentX If it's now a bookmarklet on your browser, you should click it.
(There's supposed to be instructions in one of those links...)
how to bookmark it??
@experimentX What browser are you using?
I'm using chrome and firefox
For Firefox, you should have the Bookmarks Toolbar displayed. Drag the bookmarklet into it.
17:01
"If $A$ is a square matrix, then $A$ is invertible if and only if $Ax = 0$ implies $x = 0$." - to prove this, do we only need to prove that if $A$ is invertible, $Ax = 0$ will have a unique solution, or do we also need to prove the converse?
Hmm ... thanks ... it's working
on FF
@JaydonZhao "if and only if" should be a hint.
i.e. one statement cannot be true without the other as true?
@JaydonZhao "A if and only if B" means "if A, then B, AND if B, then A".
It's a way to write two-in-one theorems.
finally ... working on chrome too .. thanks
17:09
If you want to prove an "iff" statement, that in fact means you have two theorems to prove.
hmm okay, thanks.
17:25
hello
18:08
Ah, how I love when questions are deleted while I'm answering.
18:27
Does $f_n(x) \to \bar{f}(x)$ pointwise and $x_n \to \bar{x}$ imply $f_n(x_n) \to \bar{f}(\bar{x})$? I forgot, I think not, there is some trick with uniform convergence
18:41
I found counterexample, ok.
19:26
@JM $1+1=2$. Let's first show that $1+1\le2$...
Hi @robjohn
@skullpatrol hey.. what's up?
@robjohn I just finished adding the "textbook answer" to my question ;-)
19:47
@skullpatrol so should I vote "plus 1" or "positive 1"?
19:58
@robjohn That, my friend, is a very good question :D
20:10
@robjohn i got your hint for my question here math.stackexchange.com/questions/157296/…
But i have a doubt as we have not been given the length of inradius can we our self take some value for it ...
I really don't like exams. They make me ask idiotic questions.
20:33
@meg_1997 since none was given, the best you can do is to either assign it a value, in which case you can scale all values appropriately afterwards, or carry that length everywhere as a variable, say $r$. Either is completely acceptable.
@meg_1997 besides, I gave a hint. You can scale everything by $r$ and use that in the answer.
@robjohn ok u mean to say carry that variable length everywhere even in finding the equations asked
@meg_1997 yes, if that is the way you want to go. I think either is acceptable, but carrying a variable length $r$ around is probably the safest. It depends on the instructor what is acceptable.
Is there somebody familiar with maxmin analogue of Riemann integral?
@robjohn do you think it is possible to find out the coordinates of any point with given information?
@meg_1997 except for the scaling, yes
20:47
which point?
@meg_1997 except for the scaling that comes from knowing only relative distances.
I have to go to campus soon. I won't be back for about 6 hours.
@robjohn later
Had my test today, there were error bounds questions on the test. What a useless thing to test
21:03
No I am serious, error bounds don't seem very useful since simpson's rule is mostly useless anyways
So I got that question wrong and definitely got the two revolution area thing questions wrong, so 3 wrong out of 9 at least, that is a solid D
21:35
oh lawd application to physics and engineering of area of a revolution is hard
it is pretty unfair to put physics stuff in a calculus class, now I have to learn physics, calculus and all the stuff I forgot like algebra
I don't even know how to make this into a question on this website, at least one that won't et downvotes
Can someone correct the English errors in "Just an example. Suppose you have a power plant in which the temperature of the steam entering the turbine is measured by sensors in order to be controlled. You know the MTBF (mean time between failure) figures of different types of sensors. You have to decide to install 1 or 3 sensors. In the latter case a separate device will choose the 2 more similar measurements out of the 3.
... What would be the expected reliability of each option? Consider that the rest of the plant is responsible for let's say 98% of the overall reliability. Can the use of 2 sensors have any advantage?"?
This is so incredibly frustrating, the book just randomly pulls out physics notation without explaining what it means
21:51
@Jordan "error bounds" of what?
@AméricoTavares Are there errors in that text?
@AméricoTavares I see none, BUT english is not my natice languange.
native*
The text was written by me ... I'm Portuguese.
@AméricoTavares Seems OK.
error bounds on simpson's rule
@PeterTamaroff Thanks!
21:55
There aren't any errors really but the sentence structure could be better
@Jordan Homer simpson rule.
@Jordan Ah!
@Jordan I'm watching something bout it now.
@Jordan It's seems an informal text.
I don't even know what SI means
"You have to decide to install 1 or 3 sensors, but in the latter case a separate device will choose the 2 most similar measurements of the 3." I don't know if that is any more proper but it flows a littler better
Well my question was not popular
22:01
Not popular where? Stack Exchange?
yes
@Jordan Thanks!
@Jordan Yep. I'm just a curious, I still don't know 1 var calculus.
I have a shallow idea on what it must be, but i'm not very sure.
I really wish the author would at least have a chapter teaching physics before he decides to introduce a chapter dedicated to physics
Cant you search from somewhere else?
22:08
I don't really have time to learn physics before tomorrow :P
this is so frustrating I don't know what to do
I can't learn out of this book
Search another place. Is the most viable alternative.
it isn't really anywhere else
the only place I can find it on is Paul's Calculus notes which are horrendous in my experience
@MarianoSuárezAlvarez Estás?
22:23
Am I suppose to assume any F is always force?
@Jordan I've found a youtube video with a MIT class. But I guess it does not fits your case.
a lecture would take too long to watch :(
Only viable alternative until now
pauls calculus notes are pretty bad, he assumes you know too much and omits too many steps and explanations
@Jordan Who's that?
22:37
A website that gets reccomended a lot
I think it is highly overrated
@Jordan It's quite cool, but you need to be good with Riemann Sums. He can't be lecturing you, he gives fast summaries, so don't expect great pedagogy. It seems better to use if you already know about the subject, to study.
I am decent with riemann sums I just don';t know physics and they keep pulling equations out of nowhere
It is incredibly frustrating, there will be a quiz on this tomorrow that I need to do well on because I failed the test today
@Jordan Pulling equations out of nowewhere? How so?
The height of this strip is and the width is 2a. We can use similar triangles to determine a as follows,
well that part, I can't link the math
@Jordan But he's defining it as $\Delta x$. He divided the triangle, try to read with more detail.
22:47
I don't see where 3/4 comes from or any of that
these are just bad notes on calculus
they might make sense for someone who has already learned it but they are like a wall if you haven't
I don't know what to do
I am screwed I guess
I can't learn from my book, nothing good online, I have a quiz in the morning tomorrow that I will fail unless I learn a year of physics and this chapter of calculus tonight
this just doesnt make sense to me
$\frac{a}{16-xistar} = \frac{10}{20}$ this seems impossible
I have never been this frustrated, I just feel completely helpless

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