The h Bar

Anonymous

3:00 PM

Any website or book?

Anonymous

I mean should I continue with java since I know a little bit of it?

Anonymous

Or should I start from the basics again with C

Bernardo Meurer

@JaimeGallego That's bad advice

@blue Assuming your interest in programming is not pure, but applied, you should start with Python

Anonymous

@BernardoMeurer What does "pure" programming mean?

Anonymous

I'm a complete noob. Please bear with me :-P

Bernardo Meurer

3:04 PM

@blue Pure here would mean you're interested in programming itself, not the uses for it. You want to study programming, as opposed to learn how to program

Note that both those goals are equally valid, and perhaps the latter is more suited for most

Anonymous

@BernardoMeurer Ah right. I'm more interested in applying my programming skills that just read theory

Jaime Gallego

@blue I "knew" JavaScript before starting seriously with CS and programming, but on hindsight that wouldn't have given me any advantage.

Bernardo Meurer

@blue Then pick up Python

I have a really good book if you want

Anonymous

@BernardoMeurer Which book?

Anonymous

Is it for laymen? :P

Bernardo Meurer

3:06 PM

Yes

Anonymous

Name?

Bernardo Meurer

hit me an email at meurerbernardo@gmail.com

I can send it to you

Python Crash Course

Anonymous

Okay. One minute

Jaime Gallego

@blue I do disagree with @Bernardo here. Learning from the basics worked out well for me.

And I'm not that interested in theory.

Bernardo Meurer

@JaimeGallego Because you have an interest in programming itself

Anonymous

3:07 PM

@JaimeGallego I do know the basics of classes functions and all from my school java course

Bernardo Meurer

Learning C is extremely demotivating and traumatizing for most people

Anonymous

inheritance encapsulation and all those theory I'm aware of

Bernardo Meurer

because C sucks the fun away from programming

Anonymous

I want to learn applied programming

Secret

C For starters: $$;$$

Bernardo Meurer

3:08 PM

@blue Hit me an email

Anonymous

@BernardoMeurer Yeah, just a minute

Bernardo Meurer

@JaimeGallego C is a horrible first language, look at the structure that CS50 relies on to make a good C starter course

I got good at C when I learned Python well

Anonymous

@BernardoMeurer Sent

DanielSank

@JohnRennie yes. Good portraits can be shot from a distance with a telephoto.

@Danu I didn't know what the symbols meant.

Bernardo Meurer

@blue Sent

Anonymous

3:13 PM

@BernardoMeurer Thanks! Checking it

Jaime Gallego

@BernardoMeurer The only things that were really treated as black boxes were the pointers and the input-reading functions early on. Apart from these, the basics can be learned fast.

Anonymous

It has a .mobi extension. How do I open it? :O

Jaime Gallego

@blue You have calibre?

Mithrandir24601

@JohnRennie currently 26 degrees here! I had blue eyes when I was younger, but they're now (mostly) green

Anonymous

@JaimeGallego Nope. I need to download that?

Anonymous

3:16 PM

download.cnet.com/Calibre/3000-20412_4-10910277.html

John Rennie

@blue Amazon Kindle app

Anonymous

@JohnRennie That works on PC ?

John Rennie

@blue Yes.

@blue download here

Anonymous

Ah, thanks. It's downloading :)

John Rennie

@blue Calibre will open .mobi files, but I find it a bit clunky for reading. I use it mainly for converting .mobi files to EPUB format so I can read them on my tablet.

Bernardo Meurer

3:22 PM

@blue DO NOT USE THE KINDLE APP

It is proprietary malware!

You can get a free, open source alternative here: calibre-ebook.com

Calibre works tremendously well and respects you as a human

Anonymous

Thanks people. I've finally managed to open it with both Calibre and Amazon :P

Anonymous

@BernardoMeurer I saw the first few chapters of the book. I have something to ask i.e. about half of the book on Python deals with the coding syntax and the root files. Will it be better if I work on improving my coding skills in java itself rather than learning python from stratch and then applying it to problem solving. Like, what is extra in python that learning java won't give me?

Jaime Gallego

Java is mainly an OOP language, which may not be that good for a first language.

Bernardo Meurer

@blue Screw Java

Java is a BS language

The only good thing about java is the JVM support

Anonymous

@JaimeGallego Well, BASIC was my first language

dmckee

3:33 PM

@JohnRennie You can also shot your image in a mirror. I've also used the web-cam on a laptop, which seems to generate a bit less distortion.

I think I posted a picture of myself wearing one of the Physics Stack Exchange swag shirts here once.

Anonymous

@BernardoMeurer Okay, but why ?

Anonymous

What extra can I do with python ?

Danu

2 days ago, by Danu

@DanielSank Since $U(2)$ is compact and connected, every element of $U(2)$ of the form $\exp(iA)$ for some $A\in \mathfrak u(2)\cong\mathfrak su(2)\oplus\Bbb R$, hence $A$ is a linear combination of Pauli matrices and the identity (here, I use the physicist convention for exponentiating with a factor $i$, which makes $\mathfrak u(2)$ into the space of Hermitian (as opposed to anti-Hermitian) matrices)

Bernardo Meurer

@blue tech.jonathangardner.net/wiki/Why_Java_Sucks

Danu

@DanielSank so which symbols? The $\mathfrak u(2)$ and $\mathfrak{su}(2)$?

$U(2)$ is the space of unitary matrices acting on $\Bbb C^2$, I should probably have mentioned that

$\mathfrak u(2)$ is simply the space of Hermitian matrices

and $\mathfrak su(2)$ is the space of Hermitian, traceless matrices

Jaime Gallego

3:36 PM

@blue Python is quite good for beginners because of its simplicity, which forces you to focus on the program itself, not on the syntax.

Java has its quirks and is more complicated, but go for it if you really want to.

Danu

so when I say $\mathfrak u(2)\cong \mathfrak{su}(2)\oplus \Bbb R$ I mean that if you take a Hermitian matrix $A$, you can decompose it into a traceless one, plus something proportional to the identity (with $\operatorname{tr}A/2$ on the diagonal), i.e. $A=A_0+\operatorname{tr}A/2 \cdot \operatorname{id}_2$ where $A_0$ is traceless

The Hermitian, traceless matrices form a 3-dimensional vector space spanned by the Pauli matrices, while the diagonal matrices proportional to the identity are obviously a 1-d vector space spanned by the identity.

Anonymous

@JaimeGallego Thanks. That seems reasonable

Danu

Those four matrices, Pauli + identity, give a basis of the Hermitian matrices

Now, every unitary matrix $U$ is of the form $U=e^{iA}$ where $A$ is Hermitian, hence a linear combination of Pauli + identity

And to see how $U$ acts, you just use the power series expansion. Thus, if $A$ preserves that vector in your Hilbert space then $U$ will do so too

Therefore, you only have to check it for Hermitian matrices, and therefore only for Pauli + identity, since they form a basis.

Does it all make sense now? @DanielSank

Balarka Sen

@Danu This is getting a bit old.

Danu

@BalarkaSen I found it in a 1967 paper though.

So shaddap :P

Balarka Sen

3:44 PM

no u

there's better category theory jokes than the co word play

FU

Come at me bro

Nice fite posture

3:47 PM

lel

Jaime Gallego

The original is Nighthawks, by Hopper. Incredible painting.

Balarka Sen

It's good painting but meh

Danu

I don't see why it's considered that great.

Then again, that kind of stufff is impossible to explain anyways

Balarka Sen

Maybe it's artistically significant somehow. I don't understand painting in general so it's quite possible there's some technical greatness to it.

Painting is a very very technical art, or such is the impression I get

Jaime Gallego

4:09 PM

IMO, realistic painters do not have the respect they deserve. I would rather have an Ilya Repin painting than Starry Night.

This particular one is impressive.

Balarka Sen

"I love realistic pictures. Eg The Treachery of Images"

my taste in art is nonstandard. i like the stuff which puts you on a high

Jaime Gallego

Again with the drug comparisons? ;)

Balarka Sen

sure why not man

Danu

@BalarkaSen That's funny though, because abstract art does that much more strongly for me.

Balarka Sen

Well, it depends on what you call abstract art (also, I did not just have painting in mind when I said it)

Futurist/Cubist/Vorticism? For sure!

Danu

4:20 PM

My living in Munich has predisposed me somewhat to liking the early abstract art by e.g. Kandinsky, Marc, etc.

Balarka Sen

yeah Kandinsky is weird

Danu

Don't like it?

Jaime Gallego

Spaniards have an obsession with realism ever since the Lazarillo de Tormes. Writers don't create stories of fantasy, they prefer writing realism.

Danu

In figurative art, I really liked some work by Sorolla that I saw a year or so ago

Jaime Gallego

I would never picture a guy in Zaragoza thinking of Hogwarts.

Balarka Sen

4:24 PM

Um, there has been very very surreal works in Spanish literature? I don't understand what you're saying.

@Danu heh, when it comes to these stuff, my usual preference options of "i like it" and "i don't like it" usually don't work

Danu

It doesn't come out well at all there

Looks quite different it real life.

Jaime Gallego

@BalarkaSen Yeah, they do exist, but they're exceptions to the rule. The main driving factor of fantasy literature has been Latin American influence.

Balarka Sen

Ah, yes, I was thinking of Latin American literature. I guess you were thinking of Spanish literature as opposed to Spanish-language literature.

DanielSank

4:49 PM

@Danu perhaps

dmckee

5:02 PM

@BalarkaSen It is iconic in part because it was an early example of taking the 'ordinary moments' philosophy of impressionism and doing in in the enhanced color and contrast, high-detail modernist style.

Personally I am a big fan of impressionism, but done right that modernist style can be just as striking.

And the things that the hyper-realists get up to have to be seen to be disbelieved.

Balarka Sen

Thanks, that's a nice summary.

Secret

For some reason I can see scenary in most abstract paintings

Here I see a bamboo forest

Jaime Gallego

2

That reminded me of this picture

They finally got a shot of Jupiter's poles

DanielSank

5:25 PM

@Secret "some reason" ?= You are human

Physics Meta

6:04 PM

0

Q: Deleting answers to "Homework questions"

I've recently answered the question Find the vector position of a moving object. The question surely isn't well-stated and seems like a straight-forward homework question. Two problems: 1) What I don't understand is the strict "no homework questions" on this site. Firstly, Stack Exchange aims t...

discussion

no_choice99

8:44 PM

hey guys if diffraction of visible light around objects depends on the wavelength of the light then why don't we see a rainbow like pattern in the shadows on the ground of say leaves on trees?

Jaime Gallego

8:54 PM

@no_choice99 There are several reasons for that.

no_choice99

hmm really?

i guess I'll ask the question on PSE coz i dont see it being asked ever

Jaime Gallego

You'd be hard-pressed to find double-slit interference in leaves. A gap between two leaves, for example, may diffract if it's thin enough, but the single-slit pattern is much harder to see. The only bright spot is on the center.

Also, because light from the sun is not monochromatic, the patterns get all mixed up.

no_choice99

im not looking for a double slit. diffraction occurs around objects, be it a single sphere

Anonymous

@no_choice99 Basically the reason is too many interferences occur that they overlap and you can't perceive it. But in some cases like on the back of CD's or DVD's you do see the rainbow like pattern you are talking of

Anonymous

Google search diffraction grating

Jaime Gallego

9:02 PM

@no_choice99 Yes, but even in that case it's too chaotic to see.

no_choice99

well i can clearly see the diffraction. the edges of the shadow are fuzzy as hell unless i reduce the distance between the leaves and the ground

Anonymous

@no_choice99 Well, then what's the problem? It will obviously be fuzzy

Jaime Gallego

But you don't see the colors, just the shadow's penumbra.

no_choice99

the problem is that i'd expect to see rainbow colors because the diffraction depends on the wavelength

yeah i just see the penumbra

Anonymous

@no_choice99 You can't see the individual colors. The reason being multiple interferences and irregularities in natural structures like leaves.

no_choice99

9:07 PM

i just posted the question in case you guys want to answer there

hmm but i still see diffraction occuring

it's not like it's even hard to see it. and that diffraction does depend on wavelength...

Anonymous

I don't know why you are going on saying "diffraction depends on wavelength". How does that change the fact that multiple interferences makes it impossible to see individual colors?

Anonymous

I never denied that diffraction is still occuring

no_choice99

i dont know

Anonymous

Don't know what?

no_choice99

by intuition the shorter the wavelength the less it is diffracted

xray wouldn't show fuzzy leaves is my guess

so i would expect to see redder around the edges, then greenish and then blueish very near the black shadow

that's how i think for now. how do i debug myself

Jaime Gallego

9:16 PM

The process is not as tidy as a simple dispersion.

Anonymous

The theory that you learnt for diffraction is applicable only when the opening is very very small(comparable to the wavelength of light)

Anonymous

Those red and blue and all...don't expect to observe them in reality

dmckee

9:41 PM

Guys, the reason for the penumbral shading around shadows on Earth is primarily the non-point nature of the sun.

Bernardo Meurer

@dmckee Not true. It's because the shadows are alive, and that shading is their way of expressing their feelings

dmckee

That thing is half a degree wide, so there is a region at the edge of the shadow that seems some of the sun's disk.

Yes, if you used a white point source then the patterns from the different wavelengths would be apparent in the first order and wash each other out at high orders, but that pattern is itself spread out of the extended nature of the source.

Physics Meta

11:01 PM

-1

Q: Poll: do you ignore the homework tag?

I want to tackle an teensy tiny bit of the homework debate: How many people set the homework tag on their ignore list as a way to improve their experience of the site? This is one of the arguments for keeping the tag around, but there's not much to go on regarding how important this mechanism is...

discussion homework

Bernardo Meurer

11:11 PM

@dmckee I think you will very much enjoy this easy68k.com/paulrsm/doc/trick68k.htm

Transcript for