UmbralRaptor changed the topic of #kspacademia to: https://gist.github.com/pdn4kd/164b9b85435d87afbec0c3a7e69d3e6d | Dogs are cats. Spiders are cat interferometers. | Космизм сегодня! | Document well, for tomorrow you may get mauled by a ネコバス. | <UmbralRaptor> … one of the other grad students just compared me to nomal O_o | <ferram4> I shall beat my problems to death with an engineer.
<kmath>
<mattdpearce> I'm just going to shout this. PUERTO RICANS DON'T HAVE WATER AND SO THEY'RE TRYING TO DRINK WATER FROM ***SUPERFUND… https://t.co/tttGZKdopR
e_14159- has joined #kspacademia
e_14159 has quit [Ping timeout: 383 seconds]
e_14159- is now known as e_14159
<UmbralRaptor>
AAAAAAAAAAAAAAAAAAAAAAAAA
<soundnfury>
SnoopJeDi: best planet, saturn stronk
<SnoopJeDi>
don't let Ares hear you ;)
<UmbralRaptor>
Meh. One of the problems with solar system formation models is that Mars is too small.
<SnoopJeDi>
I was just having a piss at the God of War angle
<SnoopJeDi>
too small in what way though UmbralRaptor?
<UmbralRaptor>
SnoopJeDi: AIUI, most simulations that generate a Mars get something with more like 1 earth mass instead of 0.1.
<SnoopJeDi>
simulations starting from protoplanetary masses, or...?
* SnoopJeDi
knows nothing about this subfield
<bofh>
^
<UmbralRaptor>
Protoplanets and planetesimals, I think. Though m knowledge is limited.
<SnoopJeDi>
hm, I wonder if that means the knowledge gap is the formation process or the initial conditions (or both?)
<UmbralRaptor>
To some degree both. Of course, Marses could be rare!
<SnoopJeDi>
rare or not, I love Mars
<SnoopJeDi>
and its adorable moons
<SnoopJeDi>
I know the names Phobos and Deimos are supposed to be very sombre but I just...they're so cute
<UmbralRaptor>
A planet with 4 volcanoes bigger than anything on Earth. o_O
<bofh>
I'm mostly confused as to how the heck those two came about, especially Phobos. Asteroid capture?
<UmbralRaptor>
Maybe, but there's also the possibility that they're collisional/accreted from a ring.
<bofh>
Wouldn't their relatively tiny size go against them being accreted from something else, incl. an impact?
<UmbralRaptor>
Compared with our moon, sure. But I want to say that they compare with Jupiter/Saturn/Uranus/Pluto* in moon:primary mass.
<UmbralRaptor>
*ignore Charon
<UmbralRaptor>
!wa phobos mass
<Qboid>
UmbralRaptor: Phobos | mass: 1.072×10^16 kg (kilograms)
<UmbralRaptor>
!wa deimos mass
<Qboid>
UmbralRaptor: Deimos | mass: 1.5×10^15 kg (kilograms)
<UmbralRaptor>
!wa mars mass
<Qboid>
UmbralRaptor: Mars | mass: 6.41693×10^23 kg (kilograms)
<UmbralRaptor>
o_O
<UmbralRaptor>
Okay, I was wrong.
<UmbralRaptor>
The other moons are more like 1e-4 to 1e-6, rather than 1e-9
<bofh>
also oops, I mix up Phobos and Deimos apparently wrt masses.
<bofh>
but yeah, they're *tiny*. like you can trip and fall off of Phobos, for crying out loud! (that fact will literally *never* get old)
<UmbralRaptor>
Jump to the Mars-Phobos L1 point!
<bofh>
oh gods where would that even be?
<bofh>
prolly not very far *from* Phobos, judging by the mass differences.
egg|zzz|egg has quit [Read error: Connection reset by peer]
egg|phone|egg has quit [Read error: Connection reset by peer]
egg|phone|egg has joined #kspacademia
egg|mobile|egg has joined #kspacademia
egg|phone|egg has quit [Read error: -0x1: UNKNOWN ERROR CODE (0001)]
egg|cell|egg has quit [Ping timeout: 183 seconds]
<egg|work|egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a tau Kusanagi
<egg|work|egg>
O_o at the ksp l10n
<egg|work|egg>
arguably O_o at KSP i18n APIs or lack thereof anyway
<egg|work|egg>
also the fun part where they changed to a font that has no arabic support from one that did in their i18n release
<egg|work|egg>
~ksp~
ferram4 has quit [Ping timeout: 383 seconds]
<Iskierka>
Great occurrence: finding that the example makefile given for coursework doesn't work because it's incorrect, they didn't notice because the linker on school computers is lenient, doesn't work on mine which is strict
egg|phone|egg has joined #kspacademia
egg|mobile|egg has quit [Ping timeout: 183 seconds]
egg|cell|egg has joined #kspacademia
egg|phone|egg has quit [Read error: Connection reset by peer]
<UmbralRaptor>
Iskierka: reason C et al. are bad #32770?
<Iskierka>
I mean I don't know if it indicates that. The GNU compiler very clearly defines -lm is in LDLIBS and if everyone bothered to be strict about that then there'd be no problems as it'd always be clarified quickly
<Iskierka>
and the lecturer who made this wouldn't have likely been doing it wrong for years
<Iskierka>
actually, I should look at makefiles for all the other coursework
<Iskierka>
yep, ALL the others do this also
<UmbralRaptor>
Joys.
<UmbralRaptor>
So, I got another email from Totally Not Feket Gabor.
<bofh>
LOL
<bofh>
Iskierka: yeah, -lm is not default linked, you have to specify it. what on earth compiler includes it in LDLIBS by default?
<UmbralRaptor>
bofh: My favorite thing was when one of his diagrams showed up on /r/vxjunkies
<bofh>
TIL of VXJunkies, that subreddit looks *amazing*.
<SnoopJeDi>
oh yes it is very #kspacademia
<SnoopJeDi>
but be sure to ground your positronic oscillator before you browse, a lot of people miss that in the FAQ :/
<SnoopJeDi>
my current subreddit to love is /r/AskHistorians because *gosh* the answers are detailed
<bofh>
/r/AskHistorians and /r/BadHistory/ are both amazing.
<SnoopJeDi>
I did not realize until last month that the former has a podcast
<SnoopJeDi>
not that I have much time for podcasts, but listened to a handful on a long drive to help a friend move to their new job
<Iskierka>
bofh: it doesn't appear to put it by default, but it accepts it in the LDFLAGS section instead
<Iskierka>
which the compiler in ubuntu handles strictly but the red-hat (probably) compiler doesn't
<bofh>
JPSS & not GOES, which is what I was more interested about, but still fascinating.
<Iskierka>
with all the stuff they throw on the school computers it may or may not be the same one you'd normally get in scientific linux
<SnoopJeDi>
Hadn't heard of JPSS before, but I'm very glad we have good programs and have treated them not-the-absolute-worst in the past, with the crazy season we've had
<Iskierka>
it was annoying to debug because we could clearly see the -lm WAS in the command, but then it couldn't find the math function desired. A few google searches later "oh. The config is just wrong."
egg|phone|egg has joined #kspacademia
<bofh>
SnoopJeDi: yep. also goddamn I am so glad the GOES-16 launch was this year b/c that thing has proven to be beyond invaluable for this year.
egg|cell|egg has quit [Read error: Connection reset by peer]
egg|cell|egg has joined #kspacademia
egg|phone|egg has quit [Read error: Connection reset by peer]
<SnoopJeDi>
agreed, GOES-16 is incredible
<SnoopJeDi>
I'm the sort of guy who never turns down a good picture of home, though
egg|cell|egg has quit [Read error: Connection reset by peer]
egg|phone|egg has joined #kspacademia
<SnoopJeDi>
The video of MESSENGER's fly-by is one of my favorite space things ever
egg|cell|egg has joined #kspacademia
<bofh>
SnoopJeDi: link? I've never actually seen that one.
<kmath>
<sondy> Greetings, space fans. Anyone in astronomy/astrophysics/space with cats want to run @ObservatoryCats next week? It’s easy: post cat pix.
<Ellied>
I mean, systemd, but you could do much worse
<SnoopJeDi>
RHEL is pretty okay, there's always scientific linux, too
<SnoopJeDi>
(it's a RHEL derviative)
<SnoopJeDi>
or it was, I think the new versions are CentOS
<Ellied>
I don't quite get what's, uh, scientific about Scientific.
<Ellied>
I tried installing it last year and it just didn't have a bunch of stuff in its repos that Debian does and I use frequently
APlayer has joined #kspacademia
<Iskierka>
the versions on school computers are on RH still as we discovered while debugging the -lm thing, but then they also only have java 1.7 installed
APlayer has quit [Read error: Connection reset by peer]
<SnoopJeDi>
yea Ellied it's missing a lot
<SnoopJeDi>
Fermilab is weird about everything vaguely on a computer
<kmath>
<edefic> @foophoof Dubapest and Budlin exist in a parallel dimension, they're rather peaceful places, save for the menace of hovercraft-invading eels
APlayer has joined #kspacademia
egg|cell|egg has quit [Read error: Connection reset by peer]
egg|phone|egg has joined #kspacademia
<APlayer>
Hi!
<UmbralRaptor>
!wpn APlayer
* Qboid
gives APlayer an unitary ꙮ
<APlayer>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a stabby moo
<UmbralRaptor>
ln(ꙮ) is hermetian?
<UmbralRaptor>
stabby!
<APlayer>
Honestly, I see some weird sort of tofu there
egg has joined #kspacademia
<UmbralRaptor>
It's a silly bit of Cyrillic, used for writing about seraphim.
egg was kicked from #kspacademia by UmbralRaptor [uhm]
<bofh>
the heck?
<UmbralRaptor>
I think his keyboard b0rked?
<Iskierka>
that's a, uh, first from egg
<Iskierka>
at first you just wonder if he's panicking then it starts to get more interesting
<APlayer>
I like to think he's actually running around his room and screaming that. The neighbours would be wondering by now.
egg has quit [Quit: moo.]
<Iskierka>
ak[]e[]y[] []i[]sa []s[]t[]u[]c[]k[]
<Iskierka>
turns out you can decipher his final messages
<Iskierka>
"my a key is stuck" "help" "HELPHELPHELP" "key stuck" "not sure why" "can't stop it somewho[sic]"
<APlayer>
Sorry?
egg has joined #kspacademia
<egg>
aha, plugging my keyboard out and back in again fixed it
<APlayer>
Have you tried turning it off and on again?
<Iskierka>
it took a bit to decipher the final messages
<egg>
(as you may have figured out by stripping 'a' from what I was seeing my a key was stuck)
<egg>
then I got kicked by a theropod and couldn't rejoin because turns out aaaaaaaaaaaaaa/aaaaaajaaaaaaaaoaaaaaaaaaaaiaaaaaaaaaaaaaaanaaaaaaaaaaaaaaa doesn't work as well as /join :-p
<Iskierka>
who would have thought
* APlayer
adds super glue below egg's a key
<Iskierka>
although it's always telling about how someone uses a computer that they don't recall the right-click menu :p
<APlayer>
Egg: How many times/sec did the key repeat?
<Iskierka>
or at least I assume there's a join option there
<egg>
I tried, found no such option
<Iskierka>
fair enough
<egg>
also the a key triggered stuff in the menus
<egg>
that happened to me once before, never figured out what caused it to get stuck
<egg>
anyway back to principia work
<APlayer>
Ah, wait. I had trouble repeating Iskierka's deciphering trick when I noticed I was stripping all a's. Not just the excessive ones
* APlayer
removes the spam from egg's source code
<Iskierka>
"This is a known bug that has happened before and could happen again. Anyway, time to ignore it."
<egg>
!wpn Iskierka
* Qboid
gives Iskierka a horizontally-polarised TRIAC
<egg>
Iskierka: we know that you know how to mitigate it on your end anyway :-p
<egg>
see we just need a Qboid plugin that detects that and translates what I say
<UmbralRaptor>
Regexes and/or kicks?
<egg>
UmbralRaptor: Iskierka's mitigation is more refined :-p
<UmbralRaptor>
I guess.
<APlayer>
Also, anyone of you developed desktop applications for Windows 7, using VS Community 2017?
<UmbralRaptor>
!wpn -add:adj triaxial
<Qboid>
UmbralRaptor: Adjective already added!
<egg>
!wpn UmbralRaptor
* Qboid
gives UmbralRaptor a thorium durandal which vaguely resembles a table
<APlayer>
Or rather, know a "getting started tutorial" (C++, nearly forgot to mention)
<APlayer>
?*
<Iskierka>
create a main function and go from there
* Iskierka
hides
<APlayer>
Well, there is a whole lot of GUI crap to take care of
<UmbralRaptor>
Skin the GUI, and wear its hide to scare away the other programs.
<APlayer>
Opening an "empty" desktop application project yields a mess that is beyond me to decipher
<Iskierka>
so run it and see if they've given you something that is functionally complete
<APlayer>
And googling stuff returns code that won't compile in VS 2017
<Iskierka>
then if they have ignore everything scary and just start throwing stuff in the gui-thread
<rqou>
i understand why this proof is correct, but how did they come up with the solution in the first place?
<egg>
anyway what I was trying to say was "nice, we have 2 russian speakers"
<rqou>
e.g. "sure, you have shown that X(t)=Phi_A(t, t0)X0Phi_B(
<rqou>
e.g. "sure, you have shown that X(t)=Phi_A(t, t0)*X0*Phi_B(t, t0)
<rqou>
is indeed the correct solution"
<APlayer>
egg: Who else is?
<rqou>
but how did they get this in the first place?
<rqou>
(last minute midterm studying, in case you were wondering :P )
<Iskierka>
I assume whitequark can probably speak russian
<Iskierka>
it would be unusual to live in moscow and be unable
<APlayer>
Ah
egg is now known as egg|nomz|egg
<egg|nomz|egg>
APlayer: whitequark?
<rqou>
egg|nomz|egg: help me with midterms while you're getting nomz :P :P
<APlayer>
The IRC protocol needs a way to send people a bar of chocolate if they helped you. Or if they need to ingest nomz while others need help
<rqou>
yes
<rqou>
except chocolate over in CH-land is probably better that what passes for chocolate here in the US :P
<SnoopJeDi>
APlayer, there's always a sincere "thank you!"
<APlayer>
"Please insert the chocolate into your CD drive to continue..."
<SnoopJeDi>
it's kind of shocking to me how far slightly-out-of-the-way politeness gets you in life
<APlayer>
SnoopJeDi: Well, I cannot say that this channel actually changed my life, but it definitely helped me to change it.
<SnoopJeDi>
like if you say "You helped me with X and Y by doing Z and I appreciate that" it seems to trite but it lands
<SnoopJeDi>
so trite*
<APlayer>
And if people spend an hour explaining things to as thick a person as I can sometimes be, I do not think it's bad to give them a cup of coffee or a bar of chocolate. They'd appreciate it.
<SnoopJeDi>
Not bad at all!
<APlayer>
s/an hour/multiple hours/
<Qboid>
APlayer meant to say: And if people spend multiple hours explaining things to as thick a person as I can sometimes be, I do not think it's bad to give them a cup of coffee or a bar of chocolate. They'd appreciate it.
<SnoopJeDi>
When I first started working in this lab, I accidentally nuked a FEA simulation that had been running for 20 hours or something, and I felt dreadful about it, so I got the person a Starbucks gift card to apologize. Kicked off a great working relationship
<APlayer>
How did you manage to nuke a simulation that was not touched for hours?
<SnoopJeDi>
Clever Stupidity™
<SnoopJeDi>
I was very unfamiliar with the software and naively believed it when it suggested you could suspend and resume simulations (you super cannot do this in COMSOL they are dirty filthy liars)
<SnoopJeDi>
I mean if you're that one Dutch guy on the forums you probably can, because that guy is a FEA wizard, but us mortals just have to suck it up and let the sim run to completion.
<APlayer>
Wait, so there was a simulation running on a machine for nearly a day and the machine had enough spare CPU for you to use it?
<SnoopJeDi>
Sure, FEA isn't really all that parallelizable
<SnoopJeDi>
and this was an 8-core machine
<SnoopJeDi>
I mean it *is* parallelizable but you always pay the piper when you have to aggregate. It's Complicated.
<rqou>
oh, i'm really sorry if i come across as not appreciative
<rqou>
i'm just trying to survive midterm season
<APlayer>
I mean... An FEA that takes a day should probably test more than one thing? Couldn't you parallelize that?
<SnoopJeDi>
I didn't mean to suggest that at all rqou sorry if it came across that way
<SnoopJeDi>
APlayer, it was a 3D model with strong nonlinearities and large spatial extent (w/ small geometry). There's no real way to square the circle, it's a computationally expensive program.
<APlayer>
rqou: I just randomly remembered how much time people here have spent to explain things to me, then I saw the nomz stuff and spit that out
<SnoopJeDi>
Mesh generation is probably one of the biggest places that parallelization *does* help, heh.
<rqou>
but yes, i should really send egg|nomz|egg some EUR/BTC so that he can buy his own chocolate over in CH rather than crappy Freedom Chocolate :P
<APlayer>
rqou: Because in Europe, we usually go to the supermarket and buy our chocolate with BTC. And then we drive to CH and buy some more there with EUR. :P
<rqou>
oh right, they don't use EUR
<rqou>
i forgot
<SnoopJeDi>
yep, CHF
<SnoopJeDi>
(the LHC tour page specifically mentions this I think? the cafeteria only takes one form of currency or somesuch)
<APlayer>
Actually, probably I am the one who has no idea about chocolate or I just only got to check out some tourist stuff, but I can't relate to CH having better chocolate than DE
<APlayer>
It seems more or less all the same to me.
<APlayer>
I mean, there are good brands and bad brands, but they are both there in DE as well as in CH, you just have to know which to buy
<rqou>
those crazy swiss with the pretty purple banknotes that (at least for now) have a higher value per volume density than gold :P
<APlayer>
I much more appreciate the 5 CHF coins.
<APlayer>
I used to wonder if people don't forge them, but every time I visit CH any possibility of this thought recurring just vanishes
<APlayer>
:P
<rqou>
huh, the obverse has a "representation of an alpine herdsman"
<rqou>
that's pretty cool
<APlayer>
And that too. Perhaps it's the lack of mountains and the WWII remnants, but Germany neither has all those pretty wooden huts, not any herdsmen that fit such a stereotype.
<APlayer>
And the best butter is Irish and not German. Well, Danish butter is good too. :P
<SnoopJeDi>
the best butter is schmaltz ;P
<APlayer>
I can't say I like that stuff
<SnoopJeDi>
I'm just being flippant since it's very much not butter
<APlayer>
But well, I don't like quite a bunch of stuff the majority of people does like
<SnoopJeDi>
and because I've only recently come to discover it and love it for roasting veg
<APlayer>
Cheese and Garlic are such examples. Oh, and tea.
<SnoopJeDi>
it also feels like a cool kitchen "hack" to save unused chicken skin and create something very useful with it
<APlayer>
What do you do with chicken skin usually vs. now?
<SnoopJeDi>
uh in the past I would usually just buy skinless stuff if I cooked chicken at all. Now, if I make a recipe where I don't want the skin (actually fairly rare atm), I toss it in a bag in the freezer
<SnoopJeDi>
and when the bag is full-ish, it's time to render schmaltz
<rqou>
anyways, back to currencies. i'm pretty jealous of how europe decided that "ftp-ing fixed-width text files around between banks and the federal reserve" is a shitty system
<rqou>
although here in freedom-land, they also realize that this is a shitty system
<rqou>
so they're "working on" "improving" it
<rqou>
by running the batch jobs at the federal reserve 3x a day instead of 1x a day
<UmbralRaptor>
If computers are faster than they were in the 1960s, why does it take days to add/remove funds?
<APlayer>
Actually, in Europe there is quite a few of things about the US that we rant about. At least in Germany.
<APlayer>
UmbralRaptor: Because the money "frozen" in transfer at any given time generates larger revenues than you might think
<bofh>
Iskierka: what right-click menu? :P (I'm using irssi)
<SnoopJeDi>
Finance is a bizarre social puzzle to me
<bofh>
^
<APlayer>
Likewise, rounding off penny-transfers in favour of the bank
<rqou>
APlayer: well there's that, and there's also the trivial answer of "batch jobs missing each other and having to wait a day"
<SnoopJeDi>
Like all that fuss when Brad Katsuyama came out with the beat-the-buyer-to-the-exchange thing
<SnoopJeDi>
(and the ensuing "HFT is inherently evil!" memes)
<SnoopJeDi>
(I'm of the opinion HFT is a very scummy thing, but probably a very good one to exist in a market)
<rqou>
since i'm adjacent to "sillycon valley" i probably am obligated to now insert some bullshit here about "fintech" "disruption" :P :P
<egg|nomz|egg>
rqou: french chocolate best chocolate :-p
<SnoopJeDi>
bofh, I went on a date this week with a political scientist who focuses on macro-econ stuff in Africa. It was *difficult* to keep the conversation from going deep on econ questions
<APlayer>
egg: You do live in Switzerland, don't you?
<egg|nomz|egg>
yeah but I'm french
<egg|nomz|egg>
(also afk a bit making a journal for the upcoming principia release)
<APlayer>
How does swiss chocolate compare to others around the EU?
<egg|nomz|egg>
(well not afk but won't be responding quickly)
<bofh>
SnoopJeDi: yeah that sounds incredibly complicated (& would be mostly over my head, honestly)
<APlayer>
From the POV of a resident
<SnoopJeDi>
bofh, same
<SnoopJeDi>
but that's rather ideal for the context of a date with an academic hehe
<SnoopJeDi>
rapport ezmode: "tell me about what keeps you up at night, starting from square one"
<APlayer>
Also see xkcd: Nerd Sniping
<SnoopJeDi>
pretty much
<rqou>
oh yeah, speaking of nerd sniping
<rqou>
i got nerd-sniped by that paperclip game a few days ago
<rqou>
fortunately(?) i beat it
<APlayer>
Is there some kmath functionality that provides xkcd links given a name and/or number?
<rqou>
but it has accounting/finance, and space! :P
<rqou>
(spoilers?)
<bofh>
SnoopJeDi: that's a very nice question for moments like that, going to have to remember it.
<SnoopJeDi>
oh I wouldn't phrase it *quite* that way, but it's easy enough to get an academic talking
<rqou>
linear algebra question: what's "the point" of Sylvester's Inequality?
<egg|nomz|egg>
"Elon Kerman"
<rqou>
this inequality: rank(A)+rank(B)-n <= rank(AB) <= min(rank(A), rank(B))
<SnoopJeDi>
being able to make useful statements about the rank of transformations and compositions thereof is useful?
<rqou>
i can see that, but i've never actually used the inequality itself
<rqou>
even though i did successfully prove it for homework
<SnoopJeDi>
you can interpret rank(AB) <= min(rank(A), rank(B)) as "the degeneracy of the composition is limited by the more degenerate member of the product", I think
<SnoopJeDi>
yea same not sure I've ever come across it myself
<rqou>
oh egg|nomz|egg btw my intuition for that problem i asked you about a few days ago was incorrect
<rqou>
according to the solutions, i need to use the "Bellman-Gronwall lemma"
<SnoopJeDi>
and the -n bit (where I think A is (n,m)?) is comparable in that you assume the worst case degeneracy?
<SnoopJeDi>
don't take what I say on faith I'm not thinking about it very hard or rigorously
<rqou>
yeah, n is the dimension of the "intermediate" vector space
<rqou>
so yes, i intuitive understand why that lemma has to be true
<rqou>
er, the inequality
<SnoopJeDi>
maybe I don't understand what you're asking, then
<rqou>
i'm just wondering under what circumstances would sylvester's inequality actually help me in a proof
<rqou>
because i've never actually used it anywhere
<rqou>
but it's in the lecture notes, so it must be important?
<SnoopJeDi>
anywhere you have a composition of transformations and care about the rank of the composition, heh
<SnoopJeDi>
good question for your prof in the specific context rqou, I assume this is that systems course?
<rqou>
this is linear systems
<SnoopJeDi>
they can probably give you a very specific answer to that question
<SnoopJeDi>
like a particular example of such a composition
<rqou>
which is slightly less insane than my robotics course that i'm going to be playing catch-up on after this midterm
<rqou>
the robotics course is the one where i need to find a solid block of time for someone to pretty please help me understand tensor products
<rqou>
because the way we're treating things in the course is awful
<Iskierka>
tensor = vector that doesn't have to represent a direction/magnitude and product should work the same way as with any other case of matrices & vectors
<rqou>
and then how does it end up replacing all of the weird "hat" operators and skew-symmetric matrices that egg|nomz|egg was really unhappy with?
<rqou>
tensors are particularly weird because apparently there's at least three different ways to think of them
<rqou>
"machine learning people" - it's a bigger bag of numbers
<SnoopJeDi>
this is generally true of any mathematical concept, heh
<rqou>
"linear algebra people" - a cartesian product of vector spaces and dual spaces
<rqou>
(why is this useful? idk)
<rqou>
"some other people" - somehow basis-independent transformation
<rqou>
(how? idk)
* Iskierka
: don't think about it, matrices just have defined behaviours, go with them
<rqou>
until you're trying to convince numpy that you're trying to multiply a list of vectors with a list of matrices
<rqou>
and then you will be sad because numpy's api sucks
<rqou>
and then you will need to struggle through the explanation of how to use "einsum" to get what you want
<SnoopJeDi>
yea, einsum is pretty aggravating since it ends up just doing a loop anyway
<Iskierka>
at least it's not matlab
<SnoopJeDi>
(i.e. it's not Fortran-fast)
<SnoopJeDi>
if you think numpy is bad though, beware pandas ;P
<bofh>
can't you just cffi out to lapack in that case tho? I def. have done that in the past at least.
<SnoopJeDi>
oh yes probably
<SnoopJeDi>
I've never needed anything to go that fast that badly
<SnoopJeDi>
I think the #1 case where I've used it is applying a bunch of rotation matrices to a bunch of positions where broadcasting doesn't do quite what I want
<rqou>
iirc applying some kind of "do an observation" matrix against an observation
<bofh>
I've begrudgingly had to allocate from within a segfault handler since doing paging in that manner for large stacksizes wound up being dramatically more efficient.
<bofh>
So glad I was eventually able to kill off that code tho.
* SnoopJeDi
nods
<SnoopJeDi>
yes, I know all of these words
<bofh>
Like I made sure to get rid of it for a reason, I didn't want the person dealing with the codebase to have to try to comprehend what in the everliving hell it was doing.
<bofh>
:P
<SnoopJeDi>
CS666 - Skeleton Management for Scientific Software
<SnoopJeDi>
our local machine shop course for grads is actually registered as PHYS666, heh.
<bofh>
so such a course would be *incredibly* useful for so many people in so many placea.
<bofh>
and I'm not exaggerating whatsoever.
<rqou>
machine shop is a 600-level course?
<rqou>
or is this not standard american numbering?
<bofh>
6xx is common as a starting point for grad courses.
<rqou>
ooh, "machine shop course **for grads**"
<rqou>
i see
<rqou>
afaik machine shop isn't even required here
<rqou>
just lots of math :P
<rqou>
even for mechanical engineering
<rqou>
(and yes, i do have machine shop training, even though i'm a "CS guy")
<bofh>
<shrug> so do I, I find it's an incredibly valuable skill to have, honestly.
<rqou>
linear algebra question: why are all norms equivalent in finite dimensions, but this isn't the case in infinite dimensions?
<bofh>
because the unit ball of a Banach space fails to be compact under any norm topology for infinite dimensions.
<rqou>
sure, but why?
<bofh>
alternatively, because *all* linear maps between finite-dimensional vector spaces are continuous (bounded), but this fails for infinite dimensions.
<bofh>
which direction are you more interested in, why it works for finite dimensions or why it fails for inf8nite?
<rqou>
why it fails for infinite
<rqou>
actually, more important intuition question first:
<rqou>
what's the intuition behind "null(A) is the orthogonal complement of range(A*)"
<rqou>
i've worked through the proof for this, but i still don't "get it" intuitively
<bofh>
hmm. I'm not sure I have a good intuitive explanation why either, actually. egg|nomz|egg?
<SnoopJeDi>
rqou, it's not a required course unless you wanna use the common shop. My lab used to be MOSTLY about magnet fab so every student ends up taking it, even if they're doing design work.
<SnoopJeDi>
It's actually *most* helpful to theory people to take such a course, because then hopefully they don't do drawings like an asshole with everything toleranced to 2 mils or whatever
<rqou>
"theory people" like all of UCB? :P
<SnoopJeDi>
(or just using metric in general when you absolutely should NOT be using metric)
<SnoopJeDi>
((unless you want *really* expensive tubing, I guess?))
<rqou>
heh, you obviously don't work in EE with weird metricized imperial everywhere
<SnoopJeDi>
err, I don't mean "don't ever use metric"
<rqou>
e.g. "2.54 mm pin pitch" "1.27 mm pin pitch" "2.5 mm pin pitch because i hate you"
<SnoopJeDi>
I mean don't use metric when the stock is sold in imperial
<SnoopJeDi>
Or more generally, match non-critical dimensions to stock where you can
<rqou>
EE has stuff that was originally imperial, but now the drawings are all in metric
<SnoopJeDi>
And other misc. "tricks" that if missed can increase fab/consultation costs by orders of magnitude
<SnoopJeDi>
(this happens a *lot* with detectors)
<rqou>
oh, EE doesn't really have this problem because of the power of photolithography :P
<SnoopJeDi>
right, it's probably much less a problem heh
<rqou>
i mean, it probably matters to the company making the chip package
<rqou>
which isn't me, so <shrug emoji>
<SnoopJeDi>
right but not for chip design
<rqou>
i was thinking for PCB design
<rqou>
where it doesn't matter at all
<SnoopJeDi>
same enough
<rqou>
as long as you actually got it right
<rqou>
and didn't mix up 2.54mm vs 2.5 mm (thanks japanese connector manufacturers)
<SnoopJeDi>
LOL what
<SnoopJeDi>
mm or cm?
<SnoopJeDi>
oh nvm 0.1"
<rqou>
there's a defacto standard of 0.1 inch pitch on random connectors
<rqou>
but some japanese connector manufacturers have connectors that are 2.5mm pitch instead
<SnoopJeDi>
thanks, "sigfigs"
<rqou>
for bonus points, there's usually enough tolerance that this will work for a sufficiently small number of pins
<SnoopJeDi>
hoo boy if there's a curriculum piece I'd love to be totally rid of, it might be sigfigs
<rqou>
it only stops working when the connector gets longer
<SnoopJeDi>
what a complete and total waste of everyone's time
<rqou>
<troll>just do everything with random variables instead</troll>
<SnoopJeDi>
propertly teaching error analysis is *not* as complicated as all the bullshit hand-waving
<SnoopJeDi>
like, shit, we expect our students to be aware of Pythagoras coming in, and simple error analysis is basically the same thing
<rqou>
but what if there's an exponential, or errors are correlated? :P
<SnoopJeDi>
> simple
<SnoopJeDi>
But to answer the question, you tell the students "sometimes this is complex and that's when you crack out one of a dozen tomes dedicated just to this subject to cook up your errorbars"
* SnoopJeDi
gestures to HEP
APlayer has quit [Ping timeout: 204 seconds]
<bofh>
sigfigs are utter trash snd a waste of everyone's time & can we please stop teaching them already?
<SnoopJeDi>
but ± is soooooooo complicated
<SnoopJeDi>
how can we possibly expect our students to understand that reporting 15 digits is pointless when the errorbars are in the first decimal place? they'll never grok it!
* SnoopJeDi
froths at the mouth
* bofh
glares
<SnoopJeDi>
When I taught labs I had to spend a full session unlearning whatever stupidity their chem profs had embedded
<SnoopJeDi>
(and it did seem to be universally their chem profs)
<SnoopJeDi>
hehe, reading these historical papers, 1000 μA called out as a high current
<SnoopJeDi>
not that it's small or anything, but IF ONLY YOU KNEW olde timey people
* Iskierka
looks sideways at 130W CPU at 1.2V
<SnoopJeDi>
beam current not real current :P
<SnoopJeDi>
(PSI is the world record holder at ~2.3 mA average beam current)
<SnoopJeDi>
for the proton energies I care about, anyway
<SnoopJeDi>
but mA scale is a pretty intense beam regardless, the people writing in that ~50s context aren't wrong, they just don't know enough about space charge yet
<bofh>
which is interesting since I think the vacuum tube folks learned about space charge around that time frame?
<SnoopJeDi>
(Courant-Snyder didn't publish until 1957)
<SnoopJeDi>
oh well they were almost certainly aware of it as a thing
<SnoopJeDi>
but the reaction to it was probably an ambivalent shrug because other issues dominated a bit more
<bofh>
Ahh. Point.
<SnoopJeDi>
I'm currently writing intro material for the origins of weak focusing and longitudinal dynamics, working up to "okay from cyclotrons we got synchrotrons, here's C-S strong focusing theory and whoooop let's go back to the cyclotron and shove that ish in there!"
egg|nomz|egg is now known as egg|zzz|egg
<bofh>
Now that you mention it, how did synchrotrons originate? "oops we have this annoying synchrotron radiation happening in our storage rings... wait what it's accidentally crazy useful for a bunch of things"?
<SnoopJeDi>
ah yea! so I wasn't suuuper familiar which is why I'm reading all this historical stuff (things are generally a *mess* before Courant-Snyder, but I LOVE this M.E. Rose paper it's wonderfully clear)
<SnoopJeDi>
I need to dig down this story to make sure it's true, but apparently Lawrence et al. thought they could have constant B_z for the original cyclotron
<SnoopJeDi>
didn't work, had to shim the machine to get it to work (operating under the assumption that things weren't uniform I guess?)
<bofh>
(oh probably)
<SnoopJeDi>
what they ended up de facto doing was introducing a radial gradient in B_z, which is what gives you weak focusing and what the main stuff I've been reading focuses on
<SnoopJeDi>
they were *pretty* familiar with the RF dynamics and understood the implications of leading/lagging the RF peak pretty well in terms of stability
<SnoopJeDi>
i.e. if you're ahead of the peak, a fast particle gets less oomph, a slow one gets more, so longitudinally you're fixed inside an "RF bucket" (this is literally what we call it)
<SnoopJeDi>
If you then drag the central energy (either by varying the RF frequency or by varying the magnetic field defining the reference orbit), you drag the whole beam
<SnoopJeDi>
the former is darned sophisticated even today so synchrotrons did the latter I believe
<SnoopJeDi>
I think I like the history of my field more than I like the work ?
<kmath>
<Fermilab> For the first time, the Large Hadron Collider is accelerating xenon nuclei for experiments. https://t.co/yNAd1ThYac
<bofh>
The history of accelerators certainly seems interesting, especially inasmuch as a lot of the key discoveries seem to be half accidental, half "we knew this for awhile in another context, but oh hey it perfectly applies here".
<bofh>
LOL
<bofh>
I *believe* most synchrotron light sources vary the magnetic field but that's highly tunable GHz oscillators & wideband klystrons are kind of, erm, not really a thing. Especially the latter.
<SnoopJeDi>
oh yea it's a wild ride in terms of history
<SnoopJeDi>
I have a book on the SSC/TNRLC that needs readin'
<SnoopJeDi>
although it's very much a personal perspective (I bought it 99% because it canonizes my boss being a pain in the ass)
<SnoopJeDi>
Literally a quote in it that says "This came to be what we referred to as The [Boss's Name] Problem" or something like that
<bofh>
rofl.
<bofh>
That's amazing.
<SnoopJeDi>
I like the old pictures of the machines, too. Accelerators produce a lot of fascinating aesthetic.
<SnoopJeDi>
Particularly striking to me are photos from ISR at CERN
<SnoopJeDi>
(as well as how super-duper novel "hey what we had two rings and smashed them into each other" was at that time)
<bofh>
Which is to me kind of mind-boggling honestly considering how standard that is nowadays.
<Qboid>
[#1596] title: Handle collisions with scenery as collisions | Not sure whether we want this in Chasles, but it seems cleaner and faster, and should provide better logs.... | https://github.com/mockingbirdnest/Principia/issues/1596
<kmath>
<DickKingSmith> Huge congratulations to the BBC subtitles team for perfectly capturing the spirit of 2017 through the medium of gui… https://t.co/npvaVz5kuC
<rqou>
it's full of totally insane equations and i have no idea what is happening at all
<rqou>
there are points, velocities, a giant pile of dots, and a huge mess of matrices
<egg|zzz|egg>
coordinate-happy!
<egg|zzz|egg>
but it does name some Lie groups so it has that going for it
<egg|zzz|egg>
which is nice
<rqou>
so um, first question
<rqou>
if my frame B is at the center of the sphere (slide 5/95 in the bottom right)
<rqou>
why does it even have a velocity?
<rqou>
ooh wait
<rqou>
the rotation isn't around the center of the sphere
<rqou>
the rotation is around the big cylinder
<rqou>
wait a minute
<rqou>
there's only one velocity because there's only one joint
<rqou>
so what exactly is being changed?
<rqou>
egg|zzz|egg: this feels really dumb, my "numbers representing my velocity" have to get changed just because i changed the frame of reference
<rqou>
but there's only one actual motion happening
<egg|zzz|egg>
well that's what a reference frame is?
<rqou>
sure, i guess
<rqou>
how come a matrix can somehow turn my point into a velocity?
<rqou>
that doesn't seem like it should be possible
<egg|zzz|egg>
rqou: I mean, if I tell you that an apple is moving at (1729 m/s, 420 m/s, -69 m/s) you know nothing about how fast my apple is moving with respect to you, nor in which direction, since I have not specified the reference frame
<rqou>
ok, that part makes sense
<egg|zzz|egg>
You do know that the apple is metrically Nice in that reference frame
<rqou>
now why is it possible to somehow convert a point into a velocity by multiplying a matrix?
<egg|zzz|egg>
*vomits*
<rqou>
also, this matrix has both subscripts and superscripts
<egg|zzz|egg>
ignore that, this is abusing notation in silly ways
<rqou>
how do you even typeset this?
<rqou>
V^_{AB}^A or something?
<egg|zzz|egg>
^_^
<rqou>
so the first problem is that i don't even understand how this operation is even possible
<rqou>
to somehow take a point q, multiply by a matrix, and end up with a velocity
<egg|zzz|egg>
my guess is that if you consider your position to mean "motionless at the given position in >whatever frame<", then this is just a rigid motion
<rqou>
then on the next slide (7/95 in the bottom right) there is a matrix with a dot
<rqou>
but why is the matrix changing with time?
<egg|zzz|egg>
rqou: but like this obviously needs some definitions of the notations, wasn't there a lecture of sorts to go with it?
<rqou>
the lectures are awful
<rqou>
so nobody goes to them :P
<egg|zzz|egg>
the absence of lectures leaves you with having to reverse-engineer them though, so that's tricky
<egg|zzz|egg>
those slides aren't self-standing
<rqou>
i'm looking at the textbook on the side
<rqou>
also, i did go to the lecture where these slides were used
<rqou>
but i didn't understand anything about what was happening
<rqou>
hmm ok, i see why the matrix is changing with time
<egg|zzz|egg>
I have no idea how the frames A and B are actually defined, so that makes it harder to follow anything past slide 5
<rqou>
it's in the diagram on slide 5
<egg|zzz|egg>
(also what the hell is this ninety-five-slide thing)
<egg|zzz|egg>
rqou: that's not a definition that's squiggles on paper; how do the axes rotate, if at all? how do the origins move?
<rqou>
these are the slides from the TA-run discussion section
<rqou>
there are also lecture slides
<rqou>
hmm, the lecture slides from this part seem to be missing
<rqou>
whee
<egg|zzz|egg>
bofh: want to do some egyptology on rqou's slides?
<rqou>
ok, i think i understand what the first few slides are doing
<rqou>
so the A frame doesn't move
<rqou>
the center of the cylinder is the rotation axis
<rqou>
and the sphere moves with the arm and the cylinder as they rotate
<rqou>
so the B frame is moving in a circle
<egg|zzz|egg>
where is its origin, how do its axes rotate
<rqou>
B is at the center of the sphere, and i guess the axes rotate with the cylinder+sphere thing as well?
<rqou>
you should add robots to Principa, what could go wrong?
Technicalfool_ has joined #kspacademia
<egg|zzz|egg>
if the origin of B is at the centre of the sphere, then the centre q of the sphere moves not, in contradiction to the blue expression
<rqou>
er, hmm
<rqou>
that's what i thought initially
<bofh>
egg|zzz|egg: I'll try, but this really isn't atopic I'm.hugely familiar with or good at. sec.
<rqou>
so point q obviously does move relative to the A frame
<rqou>
somehow this motion gets expressed in the B frame?
<rqou>
but the numbers corresponding to "q in the B frame" don't change
<egg|zzz|egg>
bofh: me neither, I'm a pure mathematician (or I guess an i18n engineer lately), not an egyptologist :-p
<egg|zzz|egg>
(okay i18n might be more related to egyptology but afaik there are no plans for ancient egyptian as a youtube site language)
<bofh>
touché
<rqou>
so they've basically expressed a motion vector relative to the B frame, but that's not the thing you want to integrate to get the "numbers corresponding to q in the B frame"
<rqou>
because that's obviously always (0,0,0)
<bofh>
(damn. what about Sumero-Akkadian cuneiform?)
<rqou>
hmm, the textbook doesn't make this any more clear
<egg|zzz|egg>
bofh: I've been jokingly pushing for mongolian written in mongolian, I think that would drive the CSS nuts :D
<rqou>
so the textbook just writes q_a(t)=R_{ab}(t)q_b
<rqou>
duh i guess
<rqou>
and then they try to find d/dt q_a(t)
Technicalfool has quit [Ping timeout: 383 seconds]
<rqou>
which the textbook writes as Rdot_{ab}(t) q_b
<rqou>
the textbook then doesn't say anything about v_q_b until much later
<rqou>
so i guess ignore that part?
<rqou>
oh wait
<rqou>
the textbook explains v_q_b(t) as R^T_{ab}(t)v_q_a(t)
<rqou>
so it's changed the velocity vector back into the B frame
<rqou>
but the velocity is somehow???? still doing something with the A frame
<egg|zzz|egg>
*vomits*
<egg|zzz|egg>
nope
<egg|zzz|egg>
nopenopenopenopenope
<rqou>
er, did i understand it wrong?
<egg|zzz|egg>
rqou: dunno, but if it's that it's horrible