The h Bar

Well __something__ is a name reserved for the implementation

what do you mean?

I think you can define your own __whatthefruitmethodnameisthis__() method without problems

it's just...not advised?

Sure, but maybe in the future Python might start using __whatthefruitmethodnameisthis__() to mean something

indeed

then you just don't upgrade python anymore

As I understand it, the "promise" is basically that any methods which are treated specially by the runtime environment will use that naming convention __something__(). So you can freely write your own methods whose names don't follow that pattern, and be confident that they'll never conflict with special methods used by the Python system in the future.

Some of us like upgrades :P

12:11 AM

XD

@DavidZ ahh I wasn't aware of the name mangling. I suppose I made up my own convention then

stackoverflow.com/questions/1301346/…

fun times...

welp, time to head home lol

laters

see you later

12:59 AM

@danielunderwood But there are a bunch a issues there.

uh oh

The [][] array will be contiguous (which is generally both good for vectorizing and allows good cache behavior).

The pointer structure might have all the data in one big contiguous block, but the programmer has to make it so.

But that is probably not what you are noticing.

The big issue probably related to the possibility of aliasing.

There are a lot of optimizations that the compiler can not make if the three blocks of memory have any possibility of overlapping.

I'm installing visual studio now

fun beans

I think you need the restrict keyword. Maybe.

Frankly this is not something I have looked into for some time.

There is also a question of loop ordering. If the compiler doesn't fix it for you, then your loops are not in the optimal order and will be smashing the cache more often than necessary.

I think you would be better with for (i...) for (k...) for (j...) ....

By aliasing, do you mean you have a = b * c and there's a chance a, b, and c occupy the same memory to some extent?

1:05 AM

Start by taking a few minutes to convince yourself that the two orderings do the same thing. Then think about why one is better for cache performance than the other.

that's too hard man...now I gotta worry about the order of loops??

2

._.

Then--perhaps--forget about it, because that compiler should be able to fix that for you.

@enumaris It used to be a big deal (and the "right" order depends on your language choice, too; I'm looking at you Fortran).

I've always just made the assumption that the compiler is much smarter than I am

But like I said, the compiler should be able to help these days.

I don't think I ever worried about loop ordering when writing in fortran

since I didn't know about it

1:07 AM

And I've never seen restrict used...interesting

The key issue in loop ordering is array storage sequencing. "Row major" and "column major" are the jargon words that mark a discussion of the issue.

I think fortran uses "row major"

@danielunderwood Yes.

what is this pch.h file visual studio is including...

ah I forgot to turn off precompiled headers or something...I remember this in the tutorial...

I don't see that option...hmmm...

If you're using VS, you may want to note that there's a distinction between Visual C++ and C++

Or maybe those are just compiler-specific extensions. I remember it being a thing at one point at least

1:18 AM

uhhh

meh, I'll just leave the #include "pch.h" in there

now I just need some small assignments to start my C++ coding

I don't have something I feel like building right now tho...

well nothing that is small enough that I could conceivably build it anyways

1:41 AM

@enumaris Many of the challenges at Programming Puzzles & Code Golf are both small and entertaining. Not that you would be working them for small codes size, as you want to be practicing good style.

hmmm cool :D

user301074

2:01 AM

hi from 2019 :3

hello

Hello from 2018 again!

2:50 AM

Public service announcement: SMBC is funny. Again. smbc-comics.com/comic/werewolf

Physics Meta

3:15 AM

1

Q: 2018: a year in moderation

It's New Year's Day in Stack Exchange land... A distinguishing characteristic of these sites is how they are moderated: We designed the Stack Exchange network engine to be mostly self-regulating, in that we amortize the overall moderation cost of the system across thousands of teeny-tiny sli...

ayc

4:16 AM

@Blue -2 is insane.Yesterday night it was 11 here and I was shivering bloody hell.....But you know I find it very satisfactory to find warmth when very cold rather than coolness when very hot..........Must've been pretty nice trip!

4:54 AM

it's noon now. Last night afterwards I went out to forage, seeing there were still many people on the street at 1 to 2 am though it's raining persistently. And crazily, Eslite Bookstore was full of people, some of them sleeping there. I wonder what's the meaning of sleeping in a public place during new year's eve/wee hours.

5:32 AM

the most gratifying thing I find on Facebook is there are people replying my physics questions posted there.

because I find physics engagers seem never active on Facebook.

Nobody recognizeable

6:24 AM

@JohnRennie you there ?

Happy New year to all.

@Nobodyrecognizeable morning :-)

Anonymous

6:52 AM

@ayc -2°C is totally bearable though, with sufficient clothing. It's not as bad as you think. ;)

Anonymous

I hear that in several habitable places in Canada and Russia, temperatures regularly fall down to -20°C and less. They do manage to survive and work normally. Gotta try it someday. And indeed, trying to stay warm in the cold seems waaay better than trying to stay cool in the heat. :P

surviving in cold weather is easier than studying physics in cold weather.

Anonymous

Interestingly, the Himalayan street dogs seem pretty ferocious and wild. They've developed a thick layer of fur and almost look like wolves. I guess that's their natural adaptation to the cold. Didn't spot any cat there, however.

and I find the main reason of feeling cold in cold weather in washing body (even just hands or feet) with cold water.

Anonymous

7:12 AM

Heehee, the term I was looking for is Himalayan Sheepdog.

Anonymous

> This breed may require obedience training in order to domesticate them. Training this breed may be difficult due to its independent and stubborn nature.

7:34 AM

Sounds like physics students to me ...

2

In other news, we may or may not have our first ever close up pictures of a Kuiper belt object - time will tell!

Anonymous

@JohnRennie That's not far from the truth. :D

Anonymous

@JohnRennie Woohoo! I have no idea of the latest news. Lemme see.

Anonymous

New Horizons Spacecraft Homing in on Kuiper Belt Target

It passed 2 hours ago, but it takes a while to get the data back

Anonymous

> After a 13-year journey, the piano-sized spacecraft has covered a distance of four billion miles to reach Ultima Thule in the Kuiper Belt — a donut-shaped region of ancient, rocky bodies beyond the orbit of Neptune.

Anonymous

7:39 AM

> The spacecraft will not be in contact with Earth during close approach but is programmed to send a signal home on the morning of Jan. 1 to indicate its health and whether it recorded all the expected data. The mission team expects the data to be returned over the next 20 months, with an additional year of data analysis and archiving.

Anonymous

Aha. That's some long time. I suppose we'll at least get some images in a few days?

Anonymous

I wonder how long it takes to send and receive (from four billion miles away) and process the images.

Q: How are New Horizons images sent back to Earth?

Apparently the data rate is about 1000 baud. About the same as the first modem I ever owned :-)

Anonymous

11

I'd like to understand how does New Horizons space craft send its data back to Earth, billions miles away from it. I read in a Time article: "Also, at the distance of Pluto, we can only send data back at a rate that’s comparable with an old 1990s modem. Because of that, during the encounter, we...

nasa new-horizons pluto

Anonymous

@JohnRennie Hehe. That's definitely not bad.....for something which is four billion miles away. :)

Q: How can I keep my cat off my keyboard?

7:47 AM

@Blue yes, imagine a modem with a 4 billion mile long cable :-)

Four hours transmission delay according to the top answer, so we'll know around 10:00 UTC if everything worked.

And first pictures by the end of today.

t t t t

1:35 PM

,,, mmmmmm3m /4///t

                                          mmmmm hv hy \

Loong

191

This is a common scenario when typing: When the family assembled for Sunday dinner, With their minds made up that they wouldn't get thinner On Argentine joint, potato^DR&FTGYB`kuhadrggoy867rt98wouth4bfgdhjlkhdsfghhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhf This happens beca...

technology pets

t t t t

2 years old son ^^

2:18 PM

pomegranate vinegar tastes so nice

kartik c.p

2:36 PM

@JohnRennie hi, and good morning. I have got simple question . What else in the universe has no effect on gravity ,Want know is there something existing on the universe and has no effect on the gravity (other than potons)

@kartikc.p "potons" is a dangerous typo

On first thought, I'd say massless particles

Hm, that can't be right, since they do have relativistic mass

Kugelblitz (astrophysics)

2:58 PM

@kartikc.p hi Kartik. Everything that has energy creates a gravitational field. So photons do create a gravitational field even though they are massless. It is even (theoretically) possible to create a black hole from photons. This is called a kugelblitz.

In theoretical physics, a kugelblitz (German: "ball lightning") is a concentration of heat, light or radiation so intense that its energy forms an event horizon and becomes self-trapped: according to general relativity and the equivalence of mass and energy, if enough radiation is aimed into a region, the concentration of energy can warp spacetime enough for the region to become a black hole (although this would be a black hole whose original mass-energy had been in the form of radiant energy rather than matter). In simpler terms, a kugelblitz is a black hole formed from radiation as opposed to...

3:11 PM

Happy new year to everyone from the 1% of my brain that's not under assault from a tiny gnome with a very large hammer.

Anonymous

3:41 PM

@ACuriousMind Wonder if we both are being assaulted by the same gnome. :P

vzn

Nov 18 '17 at 0:43, by Secret

Optimistic Nihilism

►

@Blue Mine says his name is Al.

Anonymous

Hmm, makes sense --- AI's hammering my left brain too. Can't think straight no more. So 2019 is the takeover year? I guess.

The only things that are going to be hammering my brain this year are the tall infographics¹

[1]: https://xkcd.com/1273/

@Blue Oh, damn non-serif font. That's a small L in my message, not an I

Loong

3:53 PM

@ACuriousMind Is that gnome Paul Simon?

4:21 PM

Is it just a giant coincidence that we have quantization procedures?

What do you mean?

Like being able to do canonical or path integral quantization. Like we should have a quantum to classical limit, but there's no reason that we could have a classical to quantum procedure is there?

I agree with the general sentiment.

kartik c.p

4:39 PM

@ACuriousMind,@JohnRennie. how can we define energy in brief terms. I can't simply visualize it i mean how it works and how can i imagine it in my brain

@kartikc.p You can't visualize energy because it is just an abstract thing. See physics.stackexchange.com/q/3014/50583, physics.stackexchange.com/q/138972/50583

Also, please just ask any questions to the room in general - there's no need to ping specific people with it unless you think they'd be especially interested in it.

@rob Why did you lock physics.stackexchange.com/q/3014/50583? When did we decide this question is off-topic?

5:28 PM

@kartikc.p the trouble is that the work energy is used in lots of different ways to mean lots of different things. So when you're asking what energy is that's a meaningless question.

5:56 PM

It worked!

New Horizons did photograph Ultima Thule!

Tweets here

NASA page here

ZeroTheHero

6:11 PM

@JohnRennie yes this is actually amazing...

FYI nytimes.com/interactive/2019/science/…

user301074

6:31 PM

In Quantum mechanics an black-hole event horizon's Area is allowed to decrease over time (and thus violate Area's theorem) because the null-energy condition is not (in general) valid in QM?

user301074

Good morning

Do long conversations in comments get retroactively moved to chat? I just saw this physics.stackexchange.com/a/120039/24839

@danielunderwood AFAIR, an objection with canonical quantization is that one can construct a mapping from the classical Hamiltonian to the quantum Hamiltonian by upgrading dynamical variables to operators (i.e., removing certain commutative structures), implying that somehow quantum mechanics can be derived from classical mechanics

6:48 PM

@danielunderwood They get moved to chat whenever a mod chances upon them and thinks they'd belong better in chat

But in your case I'd see not much benefit in preserving the conversation and rather delete it wholesale, leaving only 1 or 2 comments to alert future visitors that the content of the answer is...controversial

@GodotMisogi but is it just a coincidence that we can do that? Unless there's something deeper underlying both CM and QM, should there really be a classical to quantum mapping? I think that may be the idea behind geometric quantization, but I'm not familiar with that (or if it's even widely accepted)

@ACuriousMind yeah I didn't really understand why that one was accepted

7:04 PM

@danielunderwood I would think it's a matter of interpretation. Just because building blocks are building blocks doesn't necessarily mean their larger structures may not have similar representations to their quanta

I also just thought that the underlying interpretation is that quantum mechanics is considered to be more general because it explains certain experimental results that CM can't, and is associated with its "free-er" structure (in the sense of free groups, free algebras, etc.) with its non-commutative structure

I personally don't see a problem with "generalisations" in such an interpretation, like having second-order changes in a path integral describing QM effects and realising that we're working in low-energy limits or whatever with renormalisation, as long as the new mathematical theory conforms to experiment. But that's probably because I'm a noob at this, and don't really know what else to think

Is this question unclear or does it require some prerequisite knowledge I'm not aware of?
https://physics.stackexchange.com/questions/451577/a-question-on-interpretation-of-transitions-from-initial-to-final-states

rob

7:32 PM

@ACuriousMind I have no recollection of my state of mind when I locked that question. Maybe I thought it was too broad for our current standards, but then why lock instead of close? I plead insanity. March-me was having a rough time.

@rob Sooo...you don't object if I just unlock it again? :)

rob

@ACuriousMind Not at all. A superficial reading makes me think it might stay closed as too broad, but I'm fine being overruled there as well.

@danielunderwood I think you should think of quantization more like this: It is not "reversing the limit", it is answering the question "What is an example of a quantum system that has this classical system as its classical limit?"

Note that e.g. ordering ambiguities mean that canonical quantization is not 1-to-1, i.e. indeed picks "examples" rather than a unique quantization

@rob I've unlocked it for now; if anyone wants to VTC it the normal way they can but I don't think any of us should close it unilaterally

@ACuriousMind By ordering ambiguities you mean examples such as normal ordering v.s. Weyl ordering?

8:22 PM

@GodotMisogi yes