The h Bar

0ßelö7

12:00 AM

linux looks awful

Jasper

I think this room is one of the most interesting rooms on SE.

0ßelö7

@BernardoMeurer what is with this awful font, anyway

Bernardo Meurer

Best spreadsheet program

@0ßelö7 I don't know, I hand-configure Arch

0ßelö7

what is wrong with you

you know how much analysis you could have mastered?

Bernardo Meurer

I don't like awful fonts ;)

Eh, not much, these days I have my install time down to an hour

Jasper

12:03 AM

It seems Bernardo is a computer expert.

Bernardo Meurer

(from nothing to fully graphical desktop setup)

Jasper

I used Debian Ubuntu Mint Fedora CentOS Mageia openSUSE before.

0ßelö7

but can you prove that if $M$ is a compact 3-manifold with $\pi_1(M)=1$, then $M=S^3$?

because that takes about the same time as your routine has taken over the years

Bernardo Meurer

Fedora, Ubuntu, Mint, and Mageia are jokes IMO

Debian and OpenSUSE I respect

0ßelö7

ubuntu

heather

12:06 AM

linux can be a bit of a pain

0ßelö7

if you get that virus it can make you drop out of college :/

heather

this is one of those times

Bernardo Meurer

Linux hasn't been a pain for me in a long time (HDMI Audio problems excluded)

Jasper

I think I will go and sleep. It is 8 AM here.

Bernardo Meurer

The thing is there are a small number of pain points on Linux, they are a little to master, but once you do it'll be unlikely that you'll find issues elsewhere

0ßelö7

12:11 AM

@BernardoMeurer Done

I am the best

Bernardo Meurer

No, Chris White is the best

in Fortran

CHRIS WHITE PLEASE COME BACK

LONG LIVE CW

0ßelö7

@BernardoMeurer I will go to grad school there just so I can talk to him

he won't know it's me

Bernardo Meurer

Hello

It's me

0ßelö7

hmm, it doesn't work all the way

wtf fortran

Bernardo Meurer

You should use GDB, I'm assuming it works if you combile on gfortran with -g flag

IIRC -g flag

(Check manuals)

0ßelö7

12:15 AM

nah the compiler works

but it seems to be executing things in the wrong order

Bernardo Meurer

GDB is a debugger

not a compiler

user228700

44 mins ago, by Kaumudi. H

Say, the temperature coefficient of resistance doesn't usually vary too much with temperature, no?

user228700

Anybody?

0ßelö7

now it works

huh

I will take it!

user228700

12:21 AM

^ This is what I am asking about.

user228700

Do ping me if you have anything to say about this!

0ßelö7

@Kaumudi.H what is the doubt

user228700

Does this formula work only in the given order, in which $\alpha$ is the temperature coeffecient of resistance at 0 C and $R_0$ is the resistance at 0 C?

user228700

Ah, hmm, will it work in the general case in which $\alpha$ is the temperature coefficient of resistance at some temperature at which the resistance is $R_{\theta}$, written outside the parenthesis? It doesn't seem to work when written in the opposite order...

0ßelö7

@Kaumudi.H You're assuming that the response to temperature is linear. But you're specifically doing a Taylor expansion around 0C, so it depends on that specifically.

user228700

12:31 AM

Depends on what specifically?

0ßelö7

the zero and the scale

user228700

Ah, hmm :-/

0ßelö7

@Kaumudi.H do you know what a Taylor expansion is?

user228700

I do, yes.

0ßelö7

$R_\theta\approx R_0 + k (\theta-\theta_0)$, right?

But we assume that $\theta_0= 0 ^\circ \mathrm C$

user228700

12:32 AM

@0ßelö7 Because...

0ßelö7

because it's convenient?

user228700

Hmm.

0ßelö7

you could do 0K and then have numbers in the 300s

user228700

Alright, I think I understand it. Thank you :-)

Phase

Ocelot is this you?

0ßelö7

12:34 AM

@Kaumudi.H also, R_0 is ok to measure for a base at 0C

it would be much harder to measure at 0K :)

heather

how do i make a new directory in /usr?

user228700

@0ßelö7 Huh? What dyou mean?

0ßelö7

further, that linear relationship is good in a neighborhood of the base

heather

I tried mkdir /usr/java but it just says permission denied

0ßelö7

@Kaumudi.H is literally everything I say confusing?

user228700

12:35 AM

:-P Well, I'm dumb, so.

0ßelö7

you need to be able to measure $R_0$ and $\alpha_0$ for that model to be any good

user228700

Right.

0ßelö7

0C is a good base point, anything more "fundamental" like 0K has issues both theoretically and experimentally

user228700

Ah, right, I see.

0ßelö7

Plus you're realistically going to be working with temps close to human temps, which is around 0C.

user228700

12:36 AM

I read your previous message too quickly and didn't notice the K in front of 0.

0ßelö7

That linear model probably breaks down for large temperature changes, so you want to put the basepoint somewhere close to the actual temperatures you're working with.

user228700

Right, right, I understand it.

user228700

Thanks! :-)

0ßelö7

np

heather

phew, got java sorted out.

Phase

12:44 AM

Still awaiting confirmation @0ßelö7

0ßelö7

@Phase wot?

Phase

Is this you?

0ßelö7

@Phase no

I don't think the Earth is flat, I just don't have any evidence either way.

Phase

Then you aren't Woke'm'st

0ßelö7

I am fairly woke

Phase

12:48 AM

on a scale of globalism $\to$ Super-male-vitality everyday

where are you

0ßelö7

7-8

used to be 9 but then I calmed down

Phase

You swallowed the blue pill

you shill

0ßelö7

wtf OSX won't let me put stuff on this flash drive

@BernardoMeurer help

oh wonderful its an NTFS issue

Bernardo Meurer

Lol

0ßelö7

@BernardoMeurer little arrows on top or boldface?

Bernardo Meurer

1:01 AM

arrows on top?

0ßelö7

$\vec\omega$

Bernardo Meurer

How are those a replacement for one another?

user228700

Does anybody here completely understand the concept of voltage drop? If yes, do you have the time to help me out with it? :-P

user228700

7

Q: Why does a Resistor cause a potential drop?

I need to know the underlying physics of what exactly happens different with the electric field in the resistor than in superconducting wires. Why is it that when I connect a resistor, potential drops across its(resistor's) ends? Sorry for the silly question but I can't figure it out. I do know...

user228700

John to the rescue again! :-D Thanks @JohnR!

user228700

1:11 AM

Oh, in other news, BTW, my roommate left in the middle of the night and locked me in from the outside. I have no idea if/when she will return :-o

0ßelö7

1:22 AM

@BernardoMeurer where are you seeing those terms?

Jasper

3:12 AM

@Kaumudi.H That is why you need keys for yourself.

user228700

@Jasper Well, I do, but ours is the type of door that can be latched only on one side.

user228700

3:33 AM

@JohnR: Ping me back when you're free to chat.

Bernardo Meurer

@0ßelö7 Still here?

John Rennie

4:43 AM

@Kaumudi.H Pingggggggg

user228700

Oh, hi! :-) Morning!

John Rennie

Morning :-)

Still locked in?

user228700

Rice pudding, eh? Nice :-)

user228700

I'm getting pizza today!!

John Rennie

PIZZA!! BOOM!

(as long as it isn't pizza with Nutella)

Secret

4:47 AM

spacetelescope.org/news/heic1715

Comisterioid

Or Asteric :?

user228700

@JohnRennie :-) No, I haven't gone completely mad (just yet).

user228700

How's work going?

John Rennie

Good. I've been getting a lot done.

user228700

Nice! :-)

John Rennie

The only problem is that I'll be submitting a big invoice this month, which means I'll have a lot of cash swirling around in the bank account. And ...

user228700

4:50 AM

Me, not so much. Today is a holiday but I've got TWO exams tomorrow!

user228700

@JohnRennie NOOO!!!

user228700

:-)

user228700

Where is the line? I don't think there is one! x'D

John Rennie

... well ... there's this laptop on eBay :-)

user228700

Of course there is :-)

John Rennie

4:53 AM

Last night I was looking on the US eBay to suggest laptops to Bernardo, and they are extraordinarily cheap - virtually paying you to take them away.

user228700

Ah, wow, cool.

John Rennie

But (a) they won't ship to the UK (b) there would be large import tariffs to pay and (c) well ... I really don't need any more laptop :-)

user228700

@JohnRennie The flipside is that no one will go with me :-( Alone, again, sigh.

John Rennie

@Kaumudi.H no-one will go with you to the cafe for pizza? Are they mad? :-)

user228700

:-(

John Rennie

4:56 AM

What exams are tomorrow? Do you have to spend all day revising again?

user228700

Nope!

user228700

I've already finished revising for one and the other I can handle after pizza, lol.

John Rennie

How is it all going? Are you reasonably optimistic?

user228700

Oh, yes! :-) I've spent a fair amount of time learning both subjects so I am quite relaxed today.

user228700

Hence, the pizza :-)

John Rennie

4:59 AM

Are there exams every semester?

user228700

There are 18 exams every semester :-)

John Rennie

Or is this a special treat for first years? :-)

user228700

I've gotten through one of them so far.

John Rennie

That's an interesting way to do it. Completely different from the UK system, but I can see the argument for lots of small exams rather than having to sit just one big exam a year.

user228700

Yep, yep, their point exactly.

user228700

5:04 AM

Gchat for a minute?

Bernardo Meurer

5:21 AM

@JohnRennie!

Good morning!

John Rennie

Morning :-)

Bernardo Meurer

What's your opinion on this

santabarbara.craigslist.org/ele/d/sony-stereo-system-record/…

santabarbara.craigslist.org/ele/d/2-sony-surround-sound-floor/…

She offered me $200 for both

John Rennie

If I'm honest I don't know. I'd have to Google for reviews.

But haven't you already got a hifi much better than that?

Bernardo Meurer

@JohnRennie Can you form an opinion to complement mine? Mine is it's a fair deal

Yes

Which is in Portugal

and I'm struggling to get here

and I'm going insane

in the meantime

I can't not get home put some music and sit back while i eat

John Rennie

I doubt it's going to be great quality. Sony's regular stuff isn't notorious for being up to proper hifi standards.

But I guess $200 isn't much

I'd probably just buy a passable Bluetooth speaker then drive it from my phone or laptop.

Bernardo Meurer

5:27 AM

I'm interest in the deal for the cassette deck, FM receiver, and rack

Things which I'd like to have but also don't want to spend real money on

Amoeba down in LA sells a lot of nice cassette tapes, they're dirt cheap and are a nice gift for yourself ($5 as opposed to $20 or more for an LP)

Do you get my point?

John Rennie

The quality of the audio from cassette tapes is deplorable compared to digital audio.

I should know. I spent many years listening to cassettes

Bernardo Meurer

I know, I'm talking souvenirs not Hi-Fi

John Rennie

I feel I'm being a bit of wet rag on this. If you want the stuff then $200 seems a very good price. But ... well ... do you really want it?

Bernardo Meurer

@JohnRennie I want the cabinet, the cassette deck, and the radio. The turntable, the speakers, the amp I don't care for but I think they'll be a nice replacement in the meantime

John Rennie

Fair enough then :-)

Bernardo Meurer

5:33 AM

The radio stations here are great!

I was amazed

John Rennie

Though those are massive speakers!!

Will there be any room for you as well as the speakers? :-)

Bernardo Meurer

I have no furniture, lol

I don't even own a desk or anything

I have a mattress

no pillow

A small desk on the living room

two chairs

that's it

I use a large Amazon box the mattress came in as my couch

@ACuriousMind Can you help me understand the difference between homotopy and homeomorphism ?

@JohnRennie So yeah, they fit

Balarka Sen

Did you mean homotopy or "homotopy equivalence"?

Homeomorphism is a map, homotopy is a family of maps, which is why I am asking.

You can't really compare two completely different objects

Bernardo Meurer

@BalarkaSen I believe I mean homotopy equivalence, yes

Balarka Sen

Alright, great. Do you know what "homotopy" means?

Bernardo Meurer

5:41 AM

Like how I can say a moebius strip and a cylinder are homotopic (is that the correct terminology?)

Balarka Sen

Make that "homotopy equivalent" and that's correct.

Bernardo Meurer

@BalarkaSen Not formally

@BalarkaSen Alright, got it, ``homotopy equivalent''

Balarka Sen

The idea is the following. If $f: X \to Y$ and $g : X \to Y$ are two (continuous) maps, they are homotopic if there is a family $f_t : X \to Y$ of maps interpolating them, i.e., $f_0 = f$ and $f_1 = g$.

And this "family" has to be continuous in parameter $t$, whatever that means.

Is this on the surface clear? Don't bother about the formalism very much, think of it as interpolation between maps

Bernardo Meurer

I'm not sure what you mean by "interpolating" there

Do you just mean that every $f_t$ is equal to either $f$ or $g$?

Balarka Sen

Ah, no, merely that $f_{t = 0} = f$ and $f_{t = 1} = g$. For time $0 < t < 1$, $f_t$ can be whatever.

It's like interpolating points by polynomials

You join two points by some curve

Here you join two maps by some family of maps

Bernardo Meurer

5:47 AM

Ah, so $t\in\Bbb R$?

Balarka Sen

$t \in [0, 1]$, in particular, yep!

Bernardo Meurer

What can I say about $f_{t=0.5}$?

Assuming $f$ and $g$ are homotopic

Balarka Sen

Nothing much! $f$ and $g$ being homotopic merely means there exists some interpolating family $\{f_t\}_{t \in [0, 1]}$ going between them. There can be a lot of such families, and $f_{t = 1/2}$ would depend very much on what family you choose.

Bernardo Meurer

Alright, cool

Balarka Sen

Let's finish with the formalism since we are here so far. If $X$ and $Y$ are two (topological) spaces, we say they are "homotopy equivalent" if there is a map $f : X \to Y$ such that there is a "homotopy inverse" $g : Y \to X$. Namely, $fg : Y \to Y$ is homotopic to the identity map $\text{id} : Y \to Y$ and $gf : X \to X$ is homotopic to the identity map $\text{id} : X \to X$.

Bernardo Meurer

5:52 AM

What's an identity map?

Maps things into themselves?

Balarka Sen

Yep, just $\text{id}(y) = y$.

The map which does nothing.

Bernardo Meurer

Alright

Okay so they're homotopy equivalent if there's a function which has an inverse

Balarka Sen

Inverse only upto homotopy, though! $fg$ need not be equal to the identity map, for example.

Just homotopic to it (there's an interpolating family from $fg$ to the identity map)

Bernardo Meurer

And then the composition of the function and it's inverse is homotopic to the identity function of the domain

Balarka Sen

Yeah

Bernardo Meurer

5:54 AM

LOOK AT ME USING WORDS

Okay

Now

When you say "Inverse only up to homotopy" does this mean I can't use IFT to determine whether $g$ exists for some $f$?

Balarka Sen

Nope!

This brings us to the notion of homeomorphism, actually.

If $X$ and $Y$ are homeomorphic, what that means is there is a map $f : X \to Y$ such that there is an actual fucking inverse $g : Y \to X$. Aka, $fg = \text{id}_Y$ is the identity map $Y \to Y$, and $gf = \text{id}_X$ is the identity map $X \to X$.

Bernardo Meurer

Oh damn

So homeomorphism is like super homotopy equivalence

Like more stronk

Balarka Sen

Yeah, it's much stronger than homotopy equivalence.

Basically, if you have two geometric objects which you can deform from one to another without cutting or gluing, just bending, stretching, doing things to it, then they are homeomorphic.

It's really the right notion of "equivalence" of spaces.

Bernardo Meurer

Cool, so, will a homeomorphism maintain all properties? I.e if I apply a homeomorphism $h\colon X\to Y$ will Y retain all properties of X?

Like, idk, being closed, open, compact, so on

Balarka Sen

Very much so! All the topological properties are preserved.

For example you mentioned compact

That means the sphere ($S^2$) and the plane ($\Bbb R^2$) are not homeomorphic

Bernardo Meurer

6:00 AM

If I change the genus of a shape in my transformation it won't even be homotopy equivalent, right?

Balarka Sen

One is compact, the other ain't

@Bernardo Well, genus is something that makes sense for only a small class of 2-dimensional spaces. Surfaces, in particular. But yes, two surfaces of different genus are NOT homotopy equivalent.

The torus and the sphere are not homotopy equivalent for example.

You are absolutely correct.

Bernardo Meurer

So like if I have a disc without the origin, it's not homeomorphic to a circle?

Balarka Sen

Nope, the first one is not compact, the second one is!

They ARE homotopy equivalent though!!

Bernardo Meurer

YES

Aha!

This is cool

Are all linear transforms homeomorphisms?

Balarka Sen

topology is very cool beyond the point-set topology everyone rants about

@BernardoMeurer Yep, linear maps $\Bbb R^n \to \Bbb R^n$ are homeomorphisms.

Bernardo Meurer

6:04 AM

This makes sense

Awesome

Balarka Sen

You can just check this, it's like $f(v) = Av$ for some invertible matrix $A$, the inverse is given by $g(v) = A^{-1}v$

Bernardo Meurer

That's true, yeah

For homotopy equivalence, how can I figure out whether there's a homotopy inverse since I can't use IFT?

Balarka Sen

Technically speaking IFT doesn't actually give you an inverse, it just gives you a local inverse, for infinitely differentiable maps, and for a restricted class of spaces only (manifolds).

But yeah there's no general algorithm for finding homotopy inverse.

Bernardo Meurer

Yes, agreed

Ah, alright

Balarka Sen

There are strong-ass theorems that tells you there exists a homotopy inverse.

"Whitehead's theorem" is a big gun.

Bernardo Meurer

6:08 AM

I imagine they're a pain in the ass to apply?

Balarka Sen

It tells if you check that a certain map $f : X \to Y$ between reasonably nice spaces satisfies a series of algebraic conditions, then $f$ is a homotopy equivalence.

@BernardoMeurer Sometimes, yup. Because the algebraic conditions are not super easy to check.

Bernardo Meurer

I remember HATING using Inverse Function Theorem and Implied Function Theorem

Although usually we had to do it on really, really shitty functions

Balarka Sen

Meh. I don't like those tedious exercises

Bernardo Meurer

Yeah, well, me neither

Ask @0ßelö7 The shit they put me through

Balarka Sen

The geometric meaning is beautiful, but hardly ever explained

@BernardoMeurer You're officially a CS student now, right?

Bernardo Meurer

6:12 AM

Of which theorem?

Yes, I am

Balarka Sen

Of inverse (slash implicit) function theorem

Cool! You enjoying it?

Bernardo Meurer

Meh, I just take GE this term, but I think I'll like it better

I really hated engineering

It felt really soulless and mechanical

It was all really boring and exhaustive

Balarka Sen

Mhm. Good life choice to drop something you don't enjoy

What's GE?

samjoe

Hello friends. Could you please check this question out? It's about angular momentum:

0

Q: Angular impulse on a pivoted rod from two different points

My actual question is that does the point from which we write angular momentum relation need to be inertial? I mean do we have to be in the reference frame of a point to write angular momentum about that point? This is illustrated in the following question, particularly in Method 2 Q. Suppose we...

newtonian-mechanics angular-momentum rotational-dynamics momentum

Bernardo Meurer

@BalarkaSen How familiar are you with American higher education?

But, simply, GE = General Education

Balarka Sen

6:17 AM

Not at all familiar.

I see.

Bernardo Meurer

So, here you have a more diversified curriculum

So if you do maths or CS, oyu also have to take history, and english and some general education stuff

I think the idea is so that you don't become overspecialized, so that you actually look at other things and so on

In any way, I quite like that

Balarka Sen

Ah, gotcha

Bernardo Meurer

Well, this semester I just take GE classes, my major classes start next term

Balarka Sen

I see what you mean now. So the real fun begins next term :P

Bernardo Meurer

So I take ENG 110: Composition and Literature, ECON 102: Macroeconomics, PHIL 203: Modern Philosophy, ART 103: History of Art: Prehistoric to Gothic; ENG 120: Researching

Yeah, I'm a quite bored to be honest

Balarka Sen

6:22 AM

It's strange that you don't get to have any of your specializations on the first semester though

Bernardo Meurer

It's a "choice" I pick my classes

But none of my major classes had open spots this term

Well

None of the ones I wanted

Balarka Sen

Ah ok

Bernardo Meurer

so I chose to take GE and save major credits for the classes I actually want to take

Balarka Sen

Good idea

Bernardo Meurer

In a way it's good because I have some time for projects

But I'm struggling focusing on something

Balarka Sen

6:27 AM

heh

push through a semester squadfam

are you kidding me? fart noises? seriously?

this man is a genius

Sir Cumference

6:56 AM

@0ßelö7 How do I get papers from Nature...?

nature.com/articles/s41550-017-0256-4

Don't tell me I have to pay $100

Side question, for anyone in research: Do you often pay the journal for the application itself, or do you only pay once you're accepted?

John Rennie

Nature doesn't charge you to publish in it.

No reputable journal will charge you to publish. If a journal tries to charge you to publish run away - fast!

Sir Cumference

@JohnRennie I thought some journals charge the publisher?

Mar 30 '15 at 21:46, by user54412

Also, in the long run, it's not clear where savings would come from. My entire field (astrophysics) is by-and-large open access, but all that means is that we authors have to pay to publish. Thus to get the same amount of research we need comparatively more grant money.

Bernardo Meurer

Snarky Puppy feat. Magda Giannikou - Amour T'es Là (Family Dinner - Volume One)

►

@BalarkaSen You may enjoy this

John Rennie

Predatory open access publishing

In academic publishing, predatory open access publishing is an exploitative open-access publishing business model that involves charging publication fees to authors without providing the editorial and publishing services associated with legitimate journals (open access or not). "Beall's List", a report that had been regularly updated by Jeffrey Beall until January 2017, set forth criteria for categorizing predatory publications and lists publishers and independent journals that meet those criteria. However, Beall's list was "unpublished" by the author in January 2017 (see below for more details...

Sir Cumference

@JohnRennie Oye, it's 3am, I don't think I'll be able to get through that

But am I misunderstanding what Chris W. was talking about?

John Rennie

7:18 AM

@SirCumference Traditional journals charge their readers. You have to pay (a lot!) to subscribe to the journal.

I'm not really in touch with the current publishing scene, but I believe that Open Access journals don't charge the readers and access to them is free.

But the journals to pay their staff somehow, so they charge people to submit articles. The cost comes from your university, so in effect the universities are saving by not having to pay the subscription fee but have to pay to publish.

Which is fair I guess.

Bernardo Meurer

7:58 AM

@JohnRennie How can I bookmark a conversation?

John Rennie

star as interesting?

Bernardo Meurer

Hmm

I thought you could actually bookmark it

And give it a name

DS does it

I wanted to name it "Bernardo and Balarka talk abous homos"

Homotopy and homeomorphism

:P

John Rennie

You mean create a bookmark in your browser?

Bernardo Meurer

No, no it's a chat thing

chat.stackexchange.com/rooms/info/71/…

See

John Rennie

Aha, it's on the room menu at the top right

Bernardo Meurer

8:05 AM

Aha!

Done!

makefiles and git

Jun 8 at 15:21, 5 minutes total – 19 messages, 3 users, 0 stars

Bookmarked Jun 8 at 15:35 by Emilio Pisanty

I am very flattered :)

John Rennie

8:43 AM

FREE FOOD IN CHESTER!!!!!

Slereah

8:58 AM

god-does-not-play-dice.net

"The main task of this website is to suggest a new, Relative Scale theory of gravity based on a hypothetical Arrow of Space which springs from God (Luke 17:21)."

Balarka Sen

@Bernardo I have heard of Snarky Puppy. Not a fan.

also lol that bookmark