The h Bar

@BernardMeurer A topological space is a set $X$ with a collection of subsets $\mathcal T$ called a "topology" such that $X,\emptyset\in\mathcal T$, $\mathcal T$ is closed under union and finite intersection.

Elements of $\mathcal T$ are called "open"

Bernard Meurer

what's that funky 0?

0celo7

6:25 PM

Empty set

@Slereah can give you the definition

note the union can be infinite

Slereah

More like $\varnothing$

Definition of what

0celo7

the definition of it

the empty set

Slereah

Depends.

0celo7

is it the set such that no set is a subset of it?

Slereah

The one I usually see is $\varnothing = \{ x | x \neq x\}$

Bernard Meurer

6:26 PM

Wait, if $\mathcal T$ is a collection of subsets of $X$ then why is it that $X \in \mathcal T$ and not the other way around?

0celo7

that's not ZFC though

Bernard Meurer

or does it not make a difference?

Slereah

Because $X$ is a subset of $X$

Bernard Meurer

Fuck you guys

0celo7

what?

Bernard Meurer

6:27 PM

Lol

0celo7

@ACuriousMind help

Bernard Meurer

How is $X$ a subset of $X$?

0celo7

$\mathcal T$ is just the set of open sets

@BernardMeurer axiom of set theory

Slereah

Empty set axiom is $$\exists x \forall y. \neg y \in x$$

0celo7

lel

Bernard Meurer

6:28 PM

wat

Slereah

Well you asked

you can then prove that this set is unique and call it $\varnothing$

Bernard Meurer

Well okay so given a set $Ç$ I can state that $Ç$ will always be a subset of $Ç$?

Slereah

proofwiki.org/wiki/Empty_Set_is_Unique

Bernard Meurer

I love me some funky characters

@Slereah Oh, nice proof!

Slereah

nice and short

0celo7

6:33 PM

@BernardMeurer ok, next definition

$C\subset X$ is closed if $X-C$ is open.

THEOREM 1. $X$ and $\emptyset$ are clopen.

Can you provide the proof?

Wait wait

wrong

Guys

What

What's $X-C$? The elements in $X$ not in $C$?

Slereah

6:35 PM

Is using a laser as a murder weapon at a very large distance viable

@BernardMeurer Yes

@Slereah Not yet

The pros are

@Slereah No

Infinite range, basically

Only limited by the curvature of the earth

But on the other hand

0celo7

6:36 PM

@BernardMeurer other notation is $X\setminus C$

Slereah

I don't know the attenuation by distance

How much power does a laser beam loses with distance

0celo7

@Slereah are you trying to kill me

Bernard Meurer

AH

Slereah

In generic atmospheric conditions

@0celo7 Don't be silly

As said

Bernard Meurer

You said an open set has a complementary which is closed!

Slereah

6:37 PM

Earth's curvature is the limiting factor

And you're too far for that

0celo7

@BernardMeurer Yes

Slereah

SO FAR

Bernard Meurer

so if $X-C$ is Open, $C$ is closed, thus X is clopen!

0celo7

You could hop on a plane

Bernard Meurer

Right?

0celo7

6:37 PM

@BernardMeurer No.

Bernard Meurer

Dang

0celo7

$U$ is open if $X-U$ is closed.

Bernard Meurer

Okay

Slereah

ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790005436.pdf

Apparently it's about 1-3 dB/km

Depending on humidity

So up to a factor of 1000 per km

I'm guessing doing it from another city is out of the question

Bernard Meurer

Good luck getting that to work down here

100% humidity

Always

Slereah

6:40 PM

Do you live in Atlantis

Oh well, my murder laser rampage will have to wait for another day

I mean there are lasers powerful enough to do that, obviously

0celo7

I would go for ACM first if I were you

Slereah

But they are military lasers

A bit suspiscious to get

Bernard Meurer

@0celo7 So what's the proof?

0celo7

$X-X=\emptyset$, which is open by definition, so $X$ is closed.

$X-\emptyset=X$, which is open by definition, so $\emptyset$ is closed.

Bernard Meurer

Who the fuck came up with this crap?

Slereah

6:46 PM

So anyway

Black holes have spaghettification

Neutron stars have the lasagna phase

What other pasta based physics exists

Bernard Meurer

is spaghettification actually a thing?

Slereah

yes

Bernard Meurer

People should add a naming class to the physics curriculum

0celo7

Proof?

vzn

my personal favorite maybe something for you all to look into :) en.wikipedia.org/wiki/Flying_Spaghetti_Monster

John Rennie

6:51 PM

Pastafarianism :-)

Bernard Meurer

@JohnRennie Do you want to adopt me?

0celo7

@vzn That's offensive

John Rennie

@BernardMeurer I have not been lying awake at night considering the option.

Bernard Meurer

@JohnRennie Dang it

0celo7

ask bob

John Rennie

6:55 PM

Why do you want to be adopted? If it's to get into a European university you do realise we've just voted to leave the EU?

Bernard Meurer

@0celo7 Bob doesn't like me

vzn

@0celo7 huh? why?

Bernard Meurer

@JohnRennie Nah, you just seem like a suitable candidate

John Rennie

Thanks (I think)

0celo7

he wants your blood

@vzn I don't have to explain

ACuriousMind

6:57 PM

@JohnRennie He means you're old enough so he can quickly inherit :P

Bernard Meurer

@JohnRennie Have you built a large, exuberant fortune which I can inherit?

ACuriousMind

^see?

Bernard Meurer

@ACuriousMind You're starting to know me too well :v

vzn

@0celo7 offensive to atheists or (most) theists maybe but not agnostics presumably, not sure about nihilists :P

John Rennie

@BernardMeurer sadly not, I spent most of my money on drink, drugs and sex

0celo7

6:59 PM

@ACuriousMind If I have a continuous function defined on all of $\Bbb R$, will it be bounded above even on open sets as long as they are not all of $\Bbb R$?

Bernard Meurer

@JohnRennie Do you still have the first two?

0celo7

I know for compact sets it's bounded, of course

but if I can put the open set inside of a compact set

then apply the compact rule

it should apply to the open set inside of it, right?

ACuriousMind

@0celo7 Clearly not, consider the open set $\mathbb{R}-\{0\}$.

John Rennie

@BernardMeurer do you mean do I still indulge in the first two, and if so does that imply I stopped indulging in the third?

0celo7

@ACuriousMind I meant bounded, ACM

Bernard Meurer

7:00 PM

@JohnRennie Yes. No.

0celo7

you know what I meant

John Rennie

Bugger! I just got outbid on a VDSL router on ebay. Damn!

0celo7

open, bounded

Bernard Meurer

@JohnRennie I just specified the first two because I don't want to have sex with you

0celo7

uhhh

John Rennie

7:02 PM

@BernardMeurer Thanks (I think)

0celo7

@JohnRennie No, he's saying you're too old for him

Bernard Meurer

@0celo7 No. I'm saying I like women

John Rennie

Well matured like fine wine

0celo7

lol, sure

Bernard Meurer

Lol

0celo7

7:02 PM

@JohnRennie More like white wine gone sour

John Rennie

Or alternatively stinky and oozing noxious fluids like matured cheese :-)

Bernard Meurer

Oh god

0celo7

fuck

John Rennie

... though preferably not me

@BernardMeurer: is it a CS degree you're thinking of doing?

Bernard Meurer

@JohnRennie I shift between CS and CEng, but since I had to decide for Portugal I just said whatever and picked CEng there

but CS is cool too

vzn

7:07 PM

(gad everything ultimately deteriorates in here with 0celo7 around) :( ... hey @Bernard when does your school start anyway

Bernard Meurer

@vzn September

0celo7

what the hell

Bernard Meurer

Moving to Lisbon next month

@0celo7 When's Michelle going to Romania?

John Rennie

It's just that I don't know anyone with an interesting job in IT who did a CS or CEng degree.

vzn

@BernardMeurer cant remember did you say you didnt have family there?

0celo7

7:08 PM

didn't know she was

Bernard Meurer

@JohnRennie I've heard that before

0celo7

pretty sure she hates me anyway

Bernard Meurer

I'm fairly certain I'm not competent to graduate in anything else though

@vzn Yeah, no family

@0celo7 Boohoo

0celo7

she thinks I hate women!

no thanks to you

John Rennie

I'm sure you won't have any problem getting a good CS/CEng degree, but I think you might find the course a bit disappointing.

From my (limited) experience universities aren't into the sort of hard core hacking that's the most fun.

Bernard Meurer

7:10 PM

@JohnRennie Yeah, everyone tells me that but, hell, what else will I do?

University seems to just be shit

John Rennie

Why not just join a startup?

0celo7

Are there computer security undergrad degrees?

Bob does not associate with people who haven't gone to college @BernardMeurer

Bernard Meurer

@JohnRennie I want a degree in something

Otherwise I'll loose my inheritance

@0celo7 Neither does my family

John Rennie

Fair enough, if you want the degree then I'm sure you'll ace it with your experience.

Bernard Meurer

@0celo7 No, you do CS and focus on security

John Rennie

7:12 PM

And I'm sure you'll find lots of like minded hackers

Bernard Meurer

@JohnRennie Also there's a lot I don't know, I'm a noob still

John Rennie

If you gather together several thousand highly motivated and smart youngsters they are more or less guaranteed to get to some interesting stuff.

0celo7

>youngsters

Bernard Meurer

@JohnRennie Problem is getting into a school where the smart youngsters are :v

ACuriousMind

@BernardMeurer Wait, after your whole experience with this application process and what you told us yesterday you still believe that the smart people end up at certain schools?

John Rennie

7:15 PM

Every university has several thousand highly motivated and smart youngsters. Just because a university isn't Ivy League doesn't mean all the students are doing janitorial science.

Bernard Meurer

@ACuriousMind Well, yeah I guess they do

@JohnRennie I guess that's accurate, yeah

John Rennie

@ACuriousMind: is this answer correct in saying that uncharged particles like neutrinos do interact via the EM force courtesy of the higher loop diagrams:

2

A: Can neutrinos interact by the EM interaction and gravity?

All objects and fields that have a nonzero mass, energy, or momentum interact gravitationally, and so do neutrinos – although they're very light and hard to produce so the gravitational force from any neutrinos we know is undetectable at this time. Neutrinos also have negligible but nonzero inte...

Bernard Meurer

@dmckee AAAh ksdjaf sadf pointers halp

dmckee

@BernardMeurer Hmm?

John Rennie

I ask because I thought so and upvoted it ...

ACuriousMind

7:19 PM

@JohnRennie yes

John Rennie

Thanks, my upvote is justified then :-)

Bernard Meurer

@dmckee If I have a variable foo that has a method foo.read, and I want to pass that onto a function as a pointer so that in that function I can do bar.read() and it will actually be changing foo (pass by reference) how do I do that?

dmckee

@JohnRennie Well, you can have electromagnetic lines and loops in higher order diagrams. I wouldn't personally use the phrase "interact via the EM force", but the effect is there.

Bernard Meurer

C++ keep's crying blood whenever I try and reference a method of a pointer

@ACuriousMind Do you know/like Kvelertak?

dmckee

Uhg. Pointers to member functions are a special case with tricky syntax and nasty semantics.

Bernard Meurer

7:21 PM

@dmckee See, salkdjfhassdaf pointers!

@ChrisWhite Halp

dmckee

Or do you really mean just a pointer to object.

Bernard Meurer

1-800-CHRIS-WHITE

John Rennie

Why would you pass a pointer to the member function rather a pointer to the object?

ACuriousMind

@BernardMeurer ...are that those experimental Swedish musicians you once linked?

Bernard Meurer

@ACuriousMind That's Wintergatan, Kvelertak is a norwegian hard-rock metal-ish band

dmckee

7:22 PM

fooObj *p = new fooObj();`

allows you to access a member function (method) by

p->bar(baz, quip);

John Rennie

@BernardMeurer: In the UK Radio One has a rock show on Sunday evening, and the DJ Daniel P. Carter is very keen on Kvelertak.

Bernard Meurer

@JohnRennie I'm passing a pointer to the object, but the compiler isn't liking it when I try and access the member function

@JohnRennie Their new album is neat

0celo7

@ACuriousMind A convex set is star-shaped about any interior point, right?

dmckee

This is equivalent to (*p).bar(baz, quip) but easier to read.

Bernard Meurer

@dmckee Lemme try

John Rennie

7:24 PM

@BernardMeurer I'm not so keen on the metal end of the rock spectrum.

Bernard Meurer

@JohnRennie Do you like Jazz?

John Rennie

All my life I have hated Jazz with a passion. It is the most boring form of music there is.

dmckee

@BernardMeurer I like jazz. I really do. But I never want to sit and listen to it for more than a few minutes at a time.

But most jazz players seem to like to cut ten minute tracks.

Impedance mismatch city.

John Rennie

I used to get dragged along to Jazz clubs at uni and I found drinking myself into insensibility was the only way to survive.

0celo7

@JohnRennie yikes

even worse than pop gangster rap?

Bernard Meurer

7:26 PM

@JohnRennie Oh god hahahaha

@dmckee Some cool new Jazz: youtube.com/watch?v=pTloZPT62IM

John Rennie

But then I like psychedelia and space rock, so my taste in music is highly suspect :-)

0celo7

space rock?

John Rennie

This is fairly typical of my listening these days:

mixcloud.com/barry-mart/earth-calling-20th-july-2016

0celo7

oh god

what is this

sounds like a 60s movie soundtrack

John Rennie

It's got a stupid intro

Fast forward past it

dmckee

7:29 PM

@0celo7 Nothing can be worse than the soundtrack for Ladyhawke. Ruined what could have been a really good movie.

Bernard Meurer

@dmckee No worky

cannot convert ‘cv::CascadeClassifier’ to ‘cv::CascadeClassifier*’ for argument ‘1’ to ‘void loadFromHeader(cv::CascadeClassifier*, char*)’

0celo7

@dmckee I don't know, @BernardMeurer says my music is atrocious

Bernard Meurer

It is, it really is

0celo7

@JohnRennie this isn't bad at all

@BernardMeurer I actually listen to incredibly popular music

you don't know what you're talking about, clearly

Bernard Meurer

@0celo7 That's why it's bad

Or, actually, that's not why it's bad

0celo7

7:33 PM

what kind of logic is that

Bernard Meurer

but in recent years incredibly popular has been a marker for bad

dmckee

@BernardMeurer It says that you are trying to pass an object where it expects a pointer-to-object. But I can't help much without seeing your code.

In the code I used above, you would simply pass p as it is the pointer-to-object.

Bernard Meurer

@dmckee Here you go

It's a little messy

the function I'm trying to implement is the one at the top

dmckee

What line is throwing the error?

Bernard Meurer

11

No, wait

wrong error

23

dmckee

7:38 PM

Well, you defined faceCascade with

CascadeClassifier faceCascade;

So it is an object. Not a pointer to object.

Make line 23

loadFromHeader(&faceCascade, face_array);

or make line 21

Bernard Meurer

Oh

God

dmckee

CascadeClassifier *faceCascade = new CascadeClassifier();

Bernard Meurer

for fucks sake me

Let's see :v

@dmckee Works! Thanks!

dmckee

The former is probably better from a RAII prospectice as long you are happy with the default initialization.

Bernard Meurer

RAII?

dmckee

7:43 PM

Resource Acquisition Is Initialization. It's a set of practices for preventing memory leaks (ideally, or at least reducing their number).

If you're going to program in c++, you should look into it.

Bernard Meurer

@dmckee Reading on it now

David Z

oooh, I found a rare moment when people aren't talking about differential geometry

dmckee

No. We're talking about c++, instead. Because this is the physics chat room, that's why.

David Z

I guess these are the things we all have in common: programming and math. Everyone's specific interests in physics are too niche to provide any common ground.

dmckee

Yeah. You hear a lot of programing and technology talk in the bar at conferences, after all.

Bernard Meurer

7:57 PM

C++ is funky

David Z

well, that's one way to put it

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