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4:10 PM
@blue A Java program isn't executed line by line.
The compiler goes through the code compiling it to byte code, and the compiler makes several passes. So it won't attempt to compile the private Node first = null; until after it has processed the code defining the Node class.
It's really no different to the fact that function declarations can come after the first call to that function in the source code.
 
Anonymous
@JohnRennie Ah. I didn't know that! Thanks
 
Anonymous
Interesting. I haven't thought about this before
 
@Blue There are languages designed to support a single-pass compiler (and therefore possible to comprehend on a straight read-through). Pascal for one.
But such languages have to add extra syntax to allow programmers to break-open closed cycles in type structures and calling trees.
 
Compiler design is at the nerdy end even even for computer nerds :-)
 
E.g. `forward declaration'.
 
4:16 PM
Well C has forward declaration ...
 
Anonymous
Oh. I've heard about Pascal. I'll read about it. :)
 
@JohnRennie I can't off the top of my head think of any features of c that require more than one pass. Though I don't know of an example of a 1-pass c compiler.
 
Anonymous
But I'm now stuck with another java stuff:
 
Anonymous
 
@Blue: see
In computer programming, a one-pass compiler is a compiler that passes through the parts of each compilation unit only once, immediately translating each part into its final machine code. This is in contrast to a multi-pass compiler which converts the program into one or more intermediate representations in steps between source code and machine code, and which reprocesses the entire compilation unit in each sequential pass. This refers to the logical functioning of the compiler, not to the actual reading of the source file once only. For instance, the source file could be read once into temporary...
 
Anonymous
4:18 PM
 
Anonymous
I can't understand how they are getting N+(2+4+8+...) and how it is approximately 3N
 
Anonymous
Using GM series summation it should be something of $2^N$ order
 
@Blue no, $2^{1+\log_2N} = 2N = 2+(2+4+8+\cdots+N)$
 
Crenshaw's Let's Build a Compiler walks the reader through writing a one-pass, recursive descent compiler for a simplified pascal-like language without most of the theory typically found in the first few chapters of a compilers textbook.
 
Anonymous
@LeakyNun Wait, how did you get that?
 
Anonymous
4:20 PM
Could you explain?
 
@Blue $2+4+8+16+32+64 = 126 = 128-2 = 2\times64-2$
you only add to $N$, so you only have $\log_2N$ terms
 
Anonymous
Umm, N is not the number of terms? We are going to add upto $N$? i.e. $2+4+8+...+2^x$ where $2^x \leq N$
 
@Blue yes
2 + 4 + 8 + ... + N is what is written
not $2 + 4 + 8 + ... + 2^N$
 
Anonymous
@LeakyNun I thought N terms
 
Anonymous
:P
 
4:23 PM
if your stack has 128 items, would you need 2^128 spaces?
 
Anonymous
Okay, second problem solved. Now the first problem
 
Anonymous
I can't understand how they got N+(2+4+8+....)
 
Anonymous
I'm trying to explain my point of view
 
Anonymous
Say, we do N push operations
 
Is Java your first language?
 
Anonymous
4:25 PM
@LeakyNun Ah, BASIC was my first language. But I guess that doesn't count
 
Anonymous
Then Java
 
so you only know BASIC and Java?
 
Anonymous
@LeakyNun Yes
 
Anonymous
I'm learning C
 
ok, continue
 
vzn
4:29 PM
@Blue hey whats up are you still learning QM?
 
Anonymous
Uh, sorry. Had to go for a while
 
Anonymous
@vzn Yea
 
Anonymous
Suppose we have the array $\{1\}$
 
Anonymous
Then we double it $\{1,2\}$
 
Anonymous
So, upto this step we had 1 array access for copy
 
Anonymous
4:31 PM
And another array access for push
 
yes
 
Anonymous
Say we denote it like $1|1$
 
vzn
@Blue what did you mean youre a "high school passout"? what country are you in?
 
Anonymous
@vzn I just joined uni
 
vzn
@Blue did you graduate HS?
 
Anonymous
4:32 PM
India
 
Anonymous
@vzn How can one get into uni without passing HS :P
 
Anonymous
Umm, so then we again double it
 
vzn
@Blue just not sure what you meant by "passout"... apparently "graduate"... eg in our language "dropout" means "not graduated"
 
Anonymous
$\{1,2,3,4\}$
 
generally high school makes me pass out
so sure
 
Anonymous
4:34 PM
So, $(1+2)|(1+2)$ (push|copy)
 
vzn
probably enjoyed school at least as much as BaS
@Blue so are you studying physics? a class? does it cover QM? what is your major?
 
Anonymous
Then, again we double it $\{1,2,3,4,5,6,7,8\}$
 
Anonymous
$|(1+2+4)|(1+2+4)|$
 
vzn
what about you @BalarkaSen any interest in QM?
 
← Just trying to do this cool self-arrow thing for no good reason
4
 
Anonymous
4:36 PM
So, I getting something of the form $2(1+2+4+...N)$ @LeakyNun
 
Not particularly. I borrowed a copy of Griffth's QM once. It mostly seemed like badly parsed mathematics instead of physics to me. It's interesting, for sure.
 
vzn
@BalarkaSen congratulations you succeeded! :P
 
@Blue you need $N$ operations to push $N$ items
 
Anonymous
@vzn Electronics is my major.
 
vzn
@BalarkaSen (lol) do you have any tolerance for alternative approaches?
 
Anonymous
4:37 PM
Yeah, we do have physics courses
 
Anonymous
But not rigorous QM (Just the basics)
 
Anonymous
I'm studying QM on my own mostly
 
vzn
@Blue are you taking a physics course right now? is it reqd for your major?
 
I need a pair of young eyes to help me read some text off a really blurry image. Any volunteers?
 
Anonymous
@vzn Yes. Solid State Physics, Thermodynamics and Classical Mechanics are my current courses
 
vzn
4:39 PM
 
@vzn Alternative approach to which?
 
Anonymous
@LeakyNun But I've already included the push operations in my calculations. Am I missing something?
 
@JohnRennie post it?
 
vzn
@BalarkaSen am working on a new interpretation of QM. want to run it by some smart but "unconditioned" audience... planning to post a question on it maybe tonite...
 
isee.winrar
 
vzn
4:41 PM
huh?
 
@Blue consider $9$ elements
 
If you look at this URL then the fourth picture along shows the label on the underneath of the laptop. I need the Service Tag off that label.
 
@BalarkaSen I was just told 2 papers in good journals is necessary for a good grad school
 
@vzn i dont know much more than a layman, if u want me to look
 
vzn
@djsmiley2k (thx) any physics bkg? yeah the more the merrier :)
 
4:42 PM
If you click on the fourth picture along then hover the mouse over the image it magnifies it. But just not quite enough for me to read the service tag off the label.
 
@vzn It's a passing meme which is overused by a group of people in the math chat, nevermind. I'd like to see the question, but I can't promise I'll read it carefully. I don't really know any physics.
@0celo7 Better start writing then
 
@vzn highschool physics + plus a interest
 
@JohnRennie SERVICE TAG(S/N) 4JKRM12
 
vzn
@djsmiley2k ok cool. the prj is to try to look at classical analogs of the wavefn. it turns out much of the mathematics shows up in classical physics but it seems almost nobody really points this out much. am looking to tighten that connection.
 
@JohnRennie 1903537?62 EXPRESS SERVICE CODE
 
4:45 PM
@LeakyNun Thanks, but it isn't that. If you open this link it looks up the service tag on the Dell site. But the tag you've suggested doesn't match.
 
@JohnRennie AJKR and then 1i +c2an2't 301ee
and a 1 yr old is attacking my keyboard :D
 
@djsmiley2k :-)
 
@JohnRennie how can I know if I read it correctly?
 
@LeakyNun follow the link to the Dell web site and you'll see that 4JKRM12 is the tag for a E5440 not an E6440 as the post describes.
 
@BalarkaSen what's an easy area of math
 
4:47 PM
@JohnRennie ok
 
Is there a journal for topoi?
 
@LeakyNun I've spent ages trying to guess what the tag is and putting it into the Dell site to see if it matches, but with no luck so far.
 
hmmm
+ok that broke imgur XD
 
@0celo7 no idea
everything looks too hard
try some topological robotics; fresh branch
 
Anonymous
@BalarkaSen What's that?
 
4:55 PM
Oh it's something I heard about recently, very cool stuff
Say you have a, uh,
linkage. Right, that's the word.
 
Anonymous
Sounds like a topic for CS guys :P
 
Anonymous
Go on
 
It's actually math.
 
Anonymous
Okay
 
So a linkage is like a bunch of axes with the end of one axis attached to the front of another.
And the end of the very first axis is fixed to the origin.
Like, a thing like "V" is a linkage.
 
4:57 PM
@JohnRennie 4QKPYZ1
 
Where the first vertex of the "V" is fixed.
So it's free to move with some constraints like those, you see
The angle between the two hands of "V" is allowed to vary
It's like our hand
 
@LeakyNun well that is an E6440, but the second letter of the tag is surely a J
 
Anonymous
Oh. I think I am getting a rough idea of it.
 
@JohnRennie does it matter?
 
@LeakyNun yes, because I want the manufacture date of the laptop. The tag uniquely identifies the specific laptop so it tells you when it was made and when the warranty runs out.
 
5:00 PM
@JohnRennie alright
 
@Blue So given a linkage, which can consist of as many hands as you want, you can ask what is it's moduli space. That is basically a thing which keeps track of how much degree of freedom the linkage has.
 
@LeakyNun That's the nice thing about Dells. If you're buying secondhand the tag can be used to check all the details and even check that it hasn't been reported stolen.
 
Anonymous
So....it's like constraint analysis
 
Anonymous
(Hope that sounds right)
 
A linkage with one hand can rotate 360 degrees, so the moduli space is the circle, or as fancy mathematicians call it, "S^1". A linkage with two hands, well, each hand is allowed to rotate 360 degrees, so the moduli space is S^1 x S^1, which is a torus. And so on.
 
5:02 PM
@LeakyNun I suspect it's a lost cause. I've e-mailed the seller to ask them the tag and I'll just have to wait and see if they reply.
 
Anonymous
@BalarkaSen I see. Pretty interesting
 
@JohnRennie what's your best guess of the express service code?
 
@Blue You can also ask the more straightforward question of what are the possible motions you can get from a planar mechanical linkage.
 
@LeakyNun 4JKHM12 but that isn't correct
 
@JohnRennie I mean, the 10-digit number
 
5:08 PM
Stuff like that can happen. In fact any planar algebraic curve can be obtained from motion of a linkage.
 
@LeakyNun I can't read that at all ...
 
Anonymous
@BalarkaSen I think I heard that before....somewhere
 
Anonymous
Yeah, that's true
 
Anonymous
There is a proof also iirc
 
Yes, of course there is a proof. It's all math :P
I think it's nontrivial to obtain linear motion from linkages.
 
Anonymous
5:11 PM
But, is this really a new branch? Constraints have been studied for a long time
 
Anonymous
I'm not sure though
 
Topological robotics is, stuff like studying configuration/moduli spaces of linkages.
There's a lot of open questions and potentials in there.
 
Anonymous
@BalarkaSen Huh, I agree
 
At least, that's what someone I met in the workshop who is interested in this told me.
 
Anonymous
How were the other students you met in the workshop?
 
5:14 PM
Some were pretty cool.
The one who told me about this was actually an engineering student, who switched to math in 2010 or something and is now a grad student in TIFR
He knows his stuff
There were a few grad students from TIFR, one I met is kind of a demigod of a sort in geometry and is now going to Princeton
 
Anonymous
wow
 
Anonymous
cool stuff
 
There was a big CMI crowd
 
Anonymous
@BalarkaSen Of course. All the math nerds go to CMI :P
 
Anonymous
BTW this year I came to know a very very weird math nerd
 
5:18 PM
I had a nice lunchtime chat with a guy from CMI who smokes weed and watches movies
 
Anonymous
He was an IMO medalist
 
Anonymous
But he joined Medical
 
Anonymous
:P
 
Anonymous
X'D
 
vOv
 
Anonymous
5:19 PM
He was in the top 100 in JEE last year
 
Anonymous
Phew
 
Anonymous
He seems to be completely crazy
 
Anonymous
A doctor who is a math-nerd. Weird combo.
 
Anonymous
@BalarkaSen Well, that's not uncommon
 
Anonymous
Many people in colleges smoke weed
 
Anonymous
5:21 PM
Even in very good colleges
 
I need to make an advertisement
 
I haven't seen a random college dude who knows Tarkovsky in the night sky
 
"Selling soul for analysis writing credit"
 
@Blue I have to say I found cannabis destroys your ability to do maths for 24 hours.
 
I wonder what the longest time I've gone without any math is
 
5:22 PM
I pretty much gave it up after I discovered that.
 
Sometimes I will open a book at 3am and pretend to read
 
@Blue Kapil Pause ?
 
@JohnRennie I have heard that from actual potheads, actually.
 
Anonymous
@AlexKChen Nah. An Indian guy named Tamoghna Ghosh. He was in the same institute as me. :P
 
@Blue I remember seeing a profile pic of him on quora in FIITJEE uniform... that guy ?
 
5:24 PM
Is quora an Indian website
 
Anonymous
@AlexKChen Yes. He is in AIIMS Delhi now
 
Or are Indians that desperate for homework answers
 
How the hell he went to IMO ?! He never went to IMO, but he cleared INMO, though.
 
Anonymous
@AlexKChen He did.
 
5:25 PM
Aaaaand the chat is about JEE et al
 
@Blue Which year ? 2015 ?
 
lol
 
Anonymous
@AlexKChen 2016
 
My program hell in a nutshell:
2
Q: Hold remainder of shell script commands until PBS qsub array job completes

a.gilI am very new to shell scripting, and I am trying to write a shell pipeline that submits multiple qsub jobs, but has several commands to run in between these qsubs, which are contingent on the most recent job completing. I have been researching multiple ways to try and hold the shell script from ...

 
Hi @BalarkaSen, can you give me a tour of the interesting stuffs about algebraic curve ? (Mostly connection to NT and other stuff ?)
 
Anonymous
5:26 PM
@0celo7 If you wish, I'll stop
 
@Blue in a class
You can continue
 
Anonymous
@0celo7 That's true
 
@Blue Of course you're (or he is) lying
 
Anonymous
@AlexKChen Maybe he didn't win a medal
 
@Blue It shows you all the 6 guys from a country, and only 6 contestants from a country can participate, regardless of they get medal or not.
 
vzn
5:29 PM
@JohnRennie youre familiar with the wave eqn for classical physics right? wondering if anyone has tried to figure out exactly how it differs in QM... seen anything along those lines?
 
@BalarkaSen Did you see my question ?
 
@AlexKChen That's a too general thing to ask for.
Besides, I don't know number theory.
 
@BalarkaSen Oh really ?!?!
 
Anonymous
@AlexKChen I don't know. I know this much that he went to New Zealand for IMO (coz he was absent for about a month). Either someone gave me wrong information or he lied or the teachers who told me lied.
 
Number theory is pretty boring
There's some interesting ergodic stuff
 
5:32 PM
@Blue You can verify it: There's a Physics SE user who was in the 2016 India team (and was in this year's team too)
 
Anonymous
@AlexKChen Huh. Who?
 
I forgot the userID, but do remember seeing him on Aops.
 
@0celo7 Ergodicity is good stuff.
 
Hi, everybody.
 
Hello
@Blue IMO was never held in newzealand. Maybe it was APMO
 
 
looool
 
Anonymous
@PrathyushPoduval ah...maybe
 
Anonymous
That's more probable
 
I can really connect to this meme
 
But then I tried a google search and came to know APMO is held in the respective countries :|
 
Anonymous
5:49 PM
I really don't know the details
 
Anonymous
Maybe it was a rumour
 
Anonymous
Created by some guys at fiitjee
 
Anonymous
I never bothered to check whether he was on the list
 
@Blue BASIC counts: serious programs have been written in it.
Though many BASIC variants instill bad habits and I would encourage people to chose something else for a newbie's first language when you have influence.
 
Anonymous
@dmckee My fist language was actually Logo
 
Anonymous
5:53 PM
lol
 
Anonymous
But I feel too ashamed to mention it
 
Anonymous
:'D
 
Nothing wrong with LOGO as a language.
 
Anonymous
Ah, turtles n all :P
 
The hype surrounding it and the pathological focus on the drawing abstraction was over the top and rather nauseating.
 
Anonymous
5:56 PM
@BalarkaSen Can we continue with Linear Algebra tomorrow afternoon around 3pm-5pm? I want to wrap my CS lesson by tonight or else it keeps getting delayed.
 
Anonymous
I'm free all afternoon
 
Anonymous
If you are free I'll ping you at 3pm sharp
 
@Blue Sure
 
Anonymous
Thanks. So 3pm-5pm. :)
 
6:25 PM
@BalarkaSen I found a GSM about ergodic theory for Riemannian manifolds. No clue if I'll ever read it
 
Sid
@WrichikBasu looks like your proposal got deleted
 
My reading list has grown by 10 since last week
It does seem pretty interesting
 
6:42 PM
@JohnRennie are you still here?
 
Hi guys would appreciate some help if possible!
For a Deuterium molecule, I have that $E_l = \dfrac{\hbar^2l(l+1)}{mR^2}$.What are the allowed values of l if the total spin is 0 or 2? I think it is 0,2,4 since individually the nuclei can only have l=0,2. Would you agree?
 
The barcode reads 4jsbm12[ with checksum 104x1+20x1+74x2+83x3+66x4+77x5+17x6+18x7 = 1294 which leaves a remainder of 59 when divided by 103, corresponding to the character [, which validates my reading.
the interpreted serial tag is 4JSBM12 which does not correspond to anything.
And yes, I spent some time with a table of how to decode barcode.
I guess I'm two hours too late
 
@LeakyNun that.... is amazing
 
edit: 4JSBM12 is valid.
 
:O
@JohnRennie ^^
Ok, that is getting bookmarked, Bravo!
 
7:33 PM
@Avantgarde Holy shit things get more and more dark and (redacted: flipped) up in this album trilogy of Walker.
The Drift is a million times darker than The Tilt, and apparently Bish Bosch reviews says it's complete madness
 
@BalarkaSen I survived the first day of algebra
 
Congrats!
 
Sid
@0celo7 First day? Linear Algebra?
 
Anonymous
They are selling radioactive stuff on Amazon
 
Anonymous
wooooaaaaaauuuwwww
 
@Sid Representation theory of finite groups
Basically linear algebra with big words
 
Anonymous
lol...maybe I should start making a nuclear reactor in my backyard with this XD
 
@Blue that's my specialty
 
Anonymous
@0celo7 I know I know..your uni is the largest radioactive material importing facility in US or something. You told me. :P
 
Largest nuclear engineering school
 
Anonymous
7:49 PM
@0celo7 Oh, yes
 
and we have one of two nuclear breeder reactors in the world
 
Anonymous
I guess you already worked with radioactive stuff. Has any major injury happened in your uni campus till date?
 
Sid
@Blue Isn't that illegal or something
 
No, HF is the real danger though
@Sid No.
There are probability limits to how much U you can own
 
Anonymous
@Sid I don't think so. Many kids have already made such stuff
 
7:51 PM
I imagine it's less than the amount needed for criticality
@Blue Fusion reactors, not fission
Making a basic fusion reactor isn't impossible. Fission without explosion is much harder
And you need a LOT of metal
 
Anonymous
MIT rejected one guy because he made a nuclear reactor in his backyard (safety pedants :P)
 
Anonymous
@0celo7 Huh, but uranium can't be used for fusion. Isn't it?
 
You use light isotopes for fusion
 
Anonymous
Maybe they used some other metal
 
I would think a homemade U fission reactor would be pretty damn hard
 
Anonymous
7:53 PM
The one on Amazon is Uranium
 
Yeah I know
 
Anonymous
@0celo7 Yup. I know. Below Fe (56)
 
@Blue Well... If it's not a really, really safe reactor, it's not a good reactor, so he didn't do a good job of it...
 
The Chicago pile used like 1 ton of shielding and everyone involved still got irradiated
Actually no, that one wasn't even shielded
during the war they didn't have time for shielding lmao
At X10 they put uranium sausages into the reactor with poles
They pushed the spent fuel out of the back and into the river for cooling
the whole area is radioactive now
 
Anonymous
@Mithrandir24601 They could have taught him the safety rules. C'mon, how many high schoolers have that kind of courage and enthusiasm to build such stuff? But ok, that is open to debate.
 
Anonymous
7:56 PM
@0celo7 wah, sounds bad
 
@BalarkaSen did you get to Section 7.3 yet?
 
Sid
@0celo7 Chi town is radioactive? :o
 
@Sid X10 was in Tennessee
and yes, Tennessee is radioactive
some of it at least
Chiraq is just a war zone
 
Sid
Whoa, Tennessee is radioactive? Isn't that supposed to be bad?
 
there are some places where you should not eat the dirt, yes
actually the bigger problem is Hg
 
Anonymous
7:59 PM
I guess people are not allowed to enter those zones
 
Anonymous
What about Hg?
 
they used Hg for making bombs or something and they dumped unholy amounts of the stuff in the woods
they had no clue it was bad in the 40s
 

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