egg|nomz|egg 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> egg|nomz|egg: generally if your eyes are dewing over, that's not the weather. | <ferram4> I shall beat my problems to death with an engineer.
<kmath> <AWESoMeStarsERC> 3D printing outreach materials - work done by summer student Dean Patient and PhD student @AdamF_Astro! #scicomm https://t.co/BNqqnToQne
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<rqou> bofh: ping?
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<egg> rqou: bofh answered in the backlog
<rqou> yeah i saw that
<rqou> i wanted to discuss it further
<egg> rqou: bofh is likely asleep
<egg> it's 8:11
<rqou> ah, too early :P
<bofh> rqou: pong
<rqou> ah, good morning
<rqou> anyways, i should probably give a more complete background of what i'm trying to actually achieve
<bofh> yes, that'd upon further thought prolly be helpful, heh.
<rqou> the original problem is "perform FPGA cell placement in an analytic manner (i.e. not simulated annealing)"
<rqou> there are a number of papers describing algorithms to do this, but they all vaguely work like this:
<rqou> fix some cells at some fixed location and then try to minimize the length of wires connecting the cells using some kind of math
<rqou> "fix" the answer that the math returns so that the cell locations are all legal
<rqou> repeat this until some convergence criteria happens
<rqou> so now more specifically
<rqou> most algorithms of this type use various ways to approximate the length of wires between cells, and they usually do so in such a way as to lead to a QP problem
<rqou> the problem with just applying QP is that it tends to cause a very dense cluster of overlapping cells somewhere "in the middle" of the array
<rqou> so the fix is that they then apply various "spread the cells out" algorithms to this
<rqou> and then they add pseudo anchors (that are not movable) to the cells at each of the new locations after applying this fixup
<rqou> and then QP is applied again
<bofh> so my first thought is: how much faster/more efficient are QPs compared to simulated annealing for this problem? SA has the nice property of eggstremely low per-iteration cost, so it *may* actually be competitive. Assuming it's not...
<bofh> uhh
<rqou> it's not clear
<rqou> supposedly SA is slower for larger designs and chips
<bofh> this sounds eggstremely hacky; why not add a minimum spread to the original QP objective function?
<rqou> afaik it's because doing so is hard? :P
<rqou> one problem is that the final result needs to be in integers
<rqou> also, various algorithms use the "spreading out" phase to apply extra hacks for additional objective functions :P
<rqou> such as estimated routing congestion
<bofh> oh, so you actually have a quadratic IP. yecch.
<rqou> oh yeah, the overall problem is super-np-hard and people are just coming up with different sets of approximations for it
<rqou> ok, one paper i read claims that the reason proper constraints aren't actually used in the QP problem is because it makes the problem not convex and/or make the objective function not differentiable
<rqou> so hacks are used instead :P
<rqou> bofh: anyways, as for why conjugate gradient: i am not at all familiar with the problem domain and some papers i read said that they did that :P :P :P
<bofh> well re: super-np-hard: duh, but the right approximation often can have a very good approximation factor
<rqou> yeah, and that's why i'm reading a bunch of papers and just copying what they did :P
<bofh> rqou: so conjugate gradient is what is commonly used due to it being eggstremely simple to implement.
<bofh> (it's kinda like the RK4 of ODE solvers in that regard)
<rqou> lol i'm not familiar with ODE solvers either :P
<rqou> i just ask numpy/scipy to give me the answer and hope it's correct :P :P
<rqou> (this has run into problems before. e.g. sliding mode control (explicitly has a step discontinuity) tends to make the solvers really really sad)
<rqou> bofh: as to why i was considering fixed-point: i was scared of floating point bugs and figured that the final answer needed to be integers anyways
<rqou> seems like that's not a good tradeoff
<bofh> erm, that doesn't help you with actually getting an integer answer from an IP, you have to actually do that carefully (okay you can often use the bruteforce method, i.e. Chvátal-Gomory cuts, but those are slow as hell generally)
<bofh> it's fairly hard to make conjugate gradient do the wrong thing just due to floating-point bugs, tbh.
<rqou> what about "dumb" bugs like "is this in X=2 or X=3? why not both?"
<rqou> as long as i do all the float->int in one place the same way this should not happen right?
<bofh> okay, so an IP is not what you think it is. integer programming as-is is very NP-hard, so what is done is you solve the *LP/QP relaxation of it* (i.e. tossing out the constraint that your solution be an integer), solve *that* since it's very easy, and then carefully round your solution to *the nearest integer solution that is within the feasible region of your original problem*. wikipedia has a very
<bofh> simple example why this is a harder problem than ...
<rqou> right, i'm familiar with this
<rqou> i'm currently looking into how to implement the "carefully round" part
<rqou> part of it is silly heuristics that people wrote papers about it
<rqou> and part of it is "basic numerics stuff"
<rqou> such as "how to floating point correctly"
<rqou> or whether i should use floating point at all
<rqou> it sounds like i don't really have to worry about the "wat is numerics" part and only need to focus on the silly fpga heuristic part?
<bofh> like, conjugate gradient *is* pretty forgiving
<rqou> do you also have suggestions for faster algorithms?
<rqou> also, do you have anything on how to operate on sparse matrices?
<bofh> Use SparseBLAS and Sparspak (or w/e the latter is called, it's the canonical Lapack extension to sparse matrices).
<rqou> and what about algorithms to be faster than conjugate gradient?
<bofh> I'll reply in a sec, have to be somewhere in right now.
<bofh> egg: PRIVMSG
* egg stabs pinyin
<rqou> lol
<rqou> try jyutping :P
<egg> rqou: that seems far more sensible in its choice of latin letters for consonants
<rqou> i've always had difficulty with it because i've never formally learned either cantonese or jyutping
<rqou> JustABCProblems :P
* egg pokes pinyin in the p, j, x, etc.
<rqou> for maximum fun, use zhuyin :P :P
<egg> s/p,/b,/
<Qboid> egg meant to say: /me pokes pinyin in the b, j, x, etc.
<rqou> you have to learn weird funny symbols _and_ trip over geopolitical issues
<egg> ah yes, the best combination,
<egg> clearly the answer is to use the sumero-akkadian syllabary to write mandarin
<rqou> lolol
<egg> probably saner than Hittite :D
<rqou> but yeah, CJKV hits fun geopolitical issues all the time
<rqou> isn't it great /s
<rqou> inb4 "han unification"
<egg> rqou: tbh that + IVD is probably the sanest solution https://twitter.com/henryfhchan/status/929050914089922560
<kmath> <henryfhchan> @celestialweasel @Kazinsal @mjg59 With a total repertoire of 80,000 CJK characters (and growing), many of which sol… https://t.co/QmaRXUv3b6
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<rqou> i'm vaguely aware of IVD
<egg> rqou: that's an interesting thread on the subject ^
<rqou> nice that they're finally fixing it like a decade+ too late
<egg> rqou: the thing is fixing it required massively broadening "what is plain text", as usual
<egg> as the thread says, this used to be a font issue on top of pre-10646/Unicode encodings
<rqou> yes, i vaguely remember even magic fonts that could "convert" between simplified and traditional
<egg> but now plain text can come with selectors that say "no here it really matters that you use *this* variant for orthographic reasons"
<egg> 6 glyphs for each of U+9F8D and U+9F8C :D
<rqou> heh
<rqou> xn--xi7a needs to gain IVD variants :P
<rqou> does Qboid have a punycode converter?
<egg> no, you could poke Thomas i guess
<egg> or make another bot, we always need more bots to pet
<egg> !u 龘
<Qboid> U+9F98 CJK IDEOGRAPH-9F98 (龘)
* rqou zzz
<rqou> now i'm the one drowning in a sea of papers
<egg> haha
<egg> but are you an egg
<rqou> no
<rqou> also, fortunately, i don't have to write another paper in the end
<rqou> i just need to make some code that works
* rqou actually zzz
<kmath> <whitequark> "Anybody who manufactures [individually wrapped sliced cheese] is familiar" ah, finally, a sentence to match math t… https://t.co/aqKMe31Bom
<egg> bofh: "Apparently the consumer neither knew nor cared that these so-called slices were not actually sliced off a loaf."
<bofh> ROFL
<bofh> I mean, I figured as much, pre-sliced cheese is far too smooth on its edges to have been sliced.
<bofh> h
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<egg> !meow bofh
* Qboid meows at bofh
<bofh> !meow egg
* Qboid meows at egg
<egg> !wpn bofh
* Qboid gives bofh a Galois INTERCAL genome
<egg> UmbralRaptop: bofh: ANBOcat was chasing a shrew inside, so I moved the shrew outside to avoid having to clean up shrew parts; the cat seems not to have understood that the shrew had been moved though, and was confused
<egg> !wpn whitequark
* Qboid gives whitequark a Radon quokka
<bofh> egg: amused that a shrew got inside in the first place, tbqh.
<egg> maybe aided by the cat?
<bofh> oh, that makes sense, prolly trying to hide from it.
<whitequark> very shrewd
<APlayer> Can I assume two interplanetary departure trajectories to be reasonably similar (i.e. will arrive at target with not-too-extreme corrections either way) if the hyperbolic excess velocity (and direction) as well as the inclination are the same?
<APlayer> (@egg in particular)
<APlayer> What I am looking at exactly is estimating a departure burn as an instantaneous change of velocity, while in reality, it will be carried out as a spiralling slow burn, and the final periapsis may have a different altitude
<UmbralRaptop> egg: are you sure that ANBOcat wasn't trying to teach you to hunt?
* UmbralRaptop 🔪 sleep
* UmbralRaptop 🔪 check deposits
<Qboid> awang: whitequark left a message for you in #kspacademia [28.07.2018 09:56:16]: "poke me about flux"
<awang> whitequark: flux?
<egg> !pet whitequark
* Qboid pets whitequark
<whitequark> awang: you were gonna solder something
<awang> whitequark: Oh right
<awang> Got some eyeglasses frames where the loop holding the lens itself detatched from the part of the frame holding the glasses to your head
<awang> Unfortunately my insurance sucks, so replacing it doesn't seem that viable right now
<awang> But I happen to have a soldering kit around and was thinking of soldering the thing together
<awang> And was wondering what kind of flux would be appropriate
<awang> If that's even something to worry about
<whitequark> yes
<whitequark> what is the frame made of?
<whitequark> can you remove the lens from the part of the frame you're going to solder?
<awang> I don't know off the top of my head, unfortunately
<awang> May have to wait until I get home to get that info
<awang> Yeah, the lens can be removed
<kmath> <DreamerHyena> I believe in Exhausted Woman in Starbucks cryptid ☕ 👽 https://t.co/dNYau8eRRf
<awang> The glasses are also painted, but that can probaby be solved with a dremel/sandpaper or something
<kmath> <gvkonsta> Nells also seems to deal with the Helsinki heatwave by being even more of a derp. She’s just hanging out in this po… https://t.co/1OdKJuONUL
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<awang> Never mind, turns out I still have the frame in my backpack
<awang> Looks like I forgot to take it out
<awang> whitequark: Looks like the frame is stainless steel
<awang> idk what kind specifically
<whitequark> stainless steel is kind of a pain to solder
<whitequark> it's probably 304 or 316
<whitequark> lemme think about it
<whitequark> I think your best bet is brazing with silver solder and a small torch.
<whitequark> you don't need flux because silver solder already comes with some sorta flux.
<whitequark> lemme grab some amazon links
<whitequark> wtf
<whitequark> awang: what's your locale?
<whitequark> can you find an ACR shop nearby?
<whitequark> amazon doesn't have any decent solder of the kind I have in mind
<whitequark> nor any of the fluxes I'm looking for
<awang> whitequark: Ohio
<awang> ACR?
<awang> Oh wow
<whitequark> aircon/refrigeration
<awang> That sounds quite a bit more involved than I expected
<awang> Hmmm
<awang> We have two home improvement stores nearby, but guess those aren't sufficiently specialized to stock what you're thinking of?
<whitequark> any high-silver (>50%) flux-coated rod will do
<whitequark> cadmium-free though I think they're all cadmium-free now
<whitequark> flux doesn't have to be white, though I've personally only worked with white rods
<awang> Hrm
<whitequark> then use one of those tiny butane torches https://www.amazon.com/QG-Pencil-Welding-Soldering-Lighter/dp/B06Y2J74T8
<whitequark> doesn't have to be this one, but you need a small torch specifically
<whitequark> with a nice blue flame
<awang> Hm
<awang> Guessing using whatever electronics solder I have layout around won't cut it? :P
<awang> These are going to be interesting to find
<whitequark> stainless? absolutely not.
<awang> Also, white flux?
<whitequark> you need higher temperatures and more aggressive flux for stainless
<awang> Ah
<whitequark> mind you, there might be other ways of soldering stainless, but *this* one is the one I can put my word behind
<whitequark> because I've brazed stainless with this kind of flux specifically with excellent results
<whitequark> white flux
<whitequark> the rods I linked are coated with flux on the outside
<whitequark> it's white, and I've only used white
<whitequark> I think it's borax
<whitequark> but I'm not sure
<whitequark> I've also seen blue and orange on amazon sold rods, not sure what's up with the color
<whitequark> but I don't think the specific kind of flux matters here
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<awang> Oh
<whitequark> also, your electronics solder is probably Sn/Pb, which isn't something I would wear on my sweaty skin every day
<awang> Looks like the silver solder carried by the local home improvement store is for plumbing
<whitequark> yeah that works
<awang> I'm not sure that any of the solder sold here has lead in it, thankfully
<awang> They're all the spool kind of solder though
<awang> Not rods
<whitequark> oh then it doesn't have flux
<awang> Yeah
<whitequark> the problem is you really don't want liquid flux
<awang> The electronics solder had a rosin core, but the descriptions here don't seem to say there's any core
<whitequark> you want a flux paste
<whitequark> no, they don't make cored solder for those applications
<awang> Ah
<awang> Flux paste, flux paste...
<whitequark> ok uhh
<whitequark> this works
<awang> Does "water soluable flux" count as paste flux?
<whitequark> link?
<whitequark> oh yeah bernzomatic does good stuff in general
<whitequark> hm
<awang> Handy
<whitequark> let's see
<whitequark> no, this is SnCuAg solder with <1% of Ag
<whitequark> it's "silver-bearing"
<whitequark> you need silver solder with >50% of Ag content
<awang> Ah
<awang> Didn't realize there was a difference there
<awang> All new terminology for me
<whitequark> yeah I don't see anything in home despot
<awang> :(
<whitequark> ok so here's flux for you on amazon https://www.amazon.com/Harris-SSWF1-Stay-Brazing-White/dp/B07DGYWQML
<whitequark> $5
<whitequark> but it's $24
* awang hochos Konsole
<awang> ctrl-click for links appears to have broken :(
<awang> whitequark: Thanks for the links!
<awang> btw, what exactly makes stainless so painful to solder?
<whitequark> the other way around
<whitequark> copper is way too easy to solder
<whitequark> but also, the same things that make it stainless: the thick chromium oxide layer protecting it from rust
<whitequark> for the same reason, aluminium is incredibly painful to both solder and weld
<SnoopJeDi> can confirm
<whitequark> in case of welding, you have to do AC welding: reverse the polarity regularly to break the sapphire growing on the surface
<SnoopJeDi> my dad snapped an aluminum mast once and managed to find someone who could do the weld but jeez.
<whitequark> it's easier to braze both aluminium and stainless than weld
<whitequark> because when brazing the oxide layer doesn't grow as much, for various reasons
<awang> whitequark: Wait, so technically what I'm going to be doing with the glasses is brazing, not soldering?
<awang> Oh wow
<awang> Glad these frames don't have aluminum in them then
<awang> Oh, also
<awang> I suppose I should sand off the paint prior to any kind of soldering?
<whitequark> whitequark: yes, but soldering and brazing are an artificial distinction made just by temperature
<whitequark> I think anything over 400°C is brazing
<whitequark> the process is the same, joining parts by melting a solder and sucking it in through capillary action
<whitequark> and the use of flux preventing oxide formation on the base metal
<whitequark> where the base metal itself doesn't melt
<whitequark> er, awang ^
<whitequark> sand off the paint, yeah, preferably
<whitequark> the rest of the paint will likely flake off too after you finish
<whitequark> or at least a significant part of
<awang> I see
<awang> The torch is required because regular irons don't get hot enough?
<awang> That and I guess it might be kind of hard to heat the frames right
<awang> Is that pencil torch you linked one you use?
<whitequark> yes, not hot enough
<whitequark> the frames will be very easy to heat, they're tiny
<whitequark> I use an uhhh'
<whitequark> I use a Bernzomatic torch that can output up to something like 3 kW
<whitequark> because I use it on 1/2" copper pipe among other things
<whitequark> I suggested a pencil torch for you specifically because you want to work on these eyeglass frames, it's perfect for that
<whitequark> I mean, -I- could probably solder your frames even with the torch I have here, because I've spent a few dozens of hours messing shit up
<awang> Er
<awang> I was meaning hard to heat with a regular soldering iron
<awang> Awkward contact area
<awang> But yeah, easy with a torch
<awang> Copper pipe for your refrigeration experiment? :P
<awang> Now I'm slightly tempted to start breaking things on purpose just for excuses to solder more things
<whitequark> try to practice on some junk stainless first
<whitequark> maybe on a nut
<whitequark> get a feel of how the solder flows
<awang> Good idea
<awang> I'll have to see what I have lying around the house
<egg> whitequark: "home despot"?
<UmbralRaptop> egg: for the DIY dictator. (actual store name is Home Depot)
<egg> bofh: UmbralRaptop: aaargh the slice of cloudless vanished https://www.meteoblue.com/de/wetter/vorhersage/seeing/villequier_frankreich_2968472
<egg> UmbralRaptop: should I try some more imaging at 40ish % cloud cover, and what should I look at
<UmbralRaptop> maybe
<UmbralRaptop> Mars?
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<UmbralRaptop> !wpn -add:adj 511 keV
<Qboid> UmbralRaptop: Adjective added!
<UmbralRaptop> egg: depends on cloud locations. I'm also going to suggest eagle nebula, omega nebula, and wild duck cluster.
<rqou> wait, my friends and i are not the only one who use the "home despot" joke?
<UmbralRaptop> rqou: I thought it was ubiquitous in the US.
<SnoopJeDi> I've not heard it before
* UmbralRaptop was still somewhat surprised to see colorlessfermion use the term.
<whitequark> i picked it up from bofh
<awang> UmbralRaptop: Why 611 keV specifically?
<awang> s/6/5
<Qboid> awang meant to say: UmbralRaptop: Why 511 keV specifically?
<UmbralRaptop> awang: blame the mass of the electron, and the typical energy of a photon from the electron-positron annihilation reaction.
<SnoopJeDi> e- + e+ -> γ + γ
<UmbralRaptop> Incidentally, there's "50 Ω" in there for some reason.
<UmbralRaptop> *there as in Qboid.
<egg> UmbralRaptop: hm, those might be treed for a bit
<bofh> egg: I mean Mars is at closest Earth approach until like 2287 tonight & bright as shit; seems like the obvious target imho :p
<iximeow> it's also a reddish orange dust ball :|
<egg> UmbralRaptop: how about Cas/And/Lac
<UmbralRaptop> The dust is fading, right?
<egg> bofh: what iximeow said, it's kind of boring tbh :-p
<UmbralRaptop> BL Lac!
<UmbralRaptop> (actually, don't. It's only interesting for studying astrophysics)
<egg> what's BL lac
<UmbralRaptop> Blazar with an infamously featureless spectrum.
<egg> cat is running around
<UmbralRaptop> cat!
<egg> ohai ISS
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* egg pokes seeing with a stick
<egg> UmbralRaptop: jupiter is supposed to be potato-shaped most of the time right,
<UmbralRaptop> Jupiter, Phobos, close enough.
<egg> also there are no stars in the field so that's unstackable anyway
* egg tries deep-sky things instead
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<bofh> UmbralRaptor: yes but presumably ome can't achieve Jovian escape velocity just by tripping over your feet & falling?
* UmbralRaptor looks around for the nearest mi-go to question.
* egg stares at seeing
<egg> UmbralRaptor: so exposures longer than 10 s don't actually eggsist, right? >_>
<bofh> egg: wouldn't that just completely saturate the sensor?
<egg> the sky is dim
<egg> i'ts more that tracking and seeing issues would yield oddly shaped stars :-p
<UmbralRaptor> egg: depends on target, etc.
<UmbralRaptor> (er, bofh also)
* UmbralRaptor wonders why this phone keeps on thinking by "bofh" I mean "bodhisattva"
<SnoopJeDi> what's the difference?
<SnoopJeDi> (I just yesterday read Hesse's "Siddhartha")
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* egg pokes approaching nebulosity with a stick
<egg> UmbralRaptor: there is a great nebulosity in andromeda
<UmbralRaptor> Is the nebulosity metal rich?
<egg> probably
<egg> also optically thick
<egg> also it covers Cas, too,
<egg> it makes observing the better-known great nebulosity in andromeda a bit tricky,
<egg> also skycircle is rising
<UmbralRaptor> Are Her or Cyg clear?
<egg> Her is underground
<egg> cyg might be clear but I'm not sure it would be by the time I'm done finding anything up there
<egg> (I could install the diagonal focuser on the finder but recollimating the focuser would also lose time, and without diagonal looking up is tedious
<egg> also tbh there are a lot of great nebulosities
<egg> Mirach is clear again though
<egg> argh of course now the nebulosity is back on top of the nebulosity as soon as i start eggsposing
<bofh> this is all sounding eggstremely nebulous, tbh.
<UmbralRaptor> I'd say that this was why some places got into radio astronomy, but it only explains the UK. Australia, however…
<kmath> <sjs917> Gosnell: Sub-subgiant stars are stars that fall between the subgiant sequence and the main sequence. They tend to d… https://t.co/ZyUUMfcEnP
* awang hochos Excel
<awang> Why would zoom be an undo-able thing >:(
<awang> And why does "redo" keep redoing past the top of the undo stack
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* egg takes some darks
<egg> !choose processing time|zzz time
<Qboid> egg: Your options are: processing time, zzz time. My choice: processing time
<egg> ;choose processing time|zzz time
<kmath> egg: processing time
<egg> stabbity choose processing time|zzz time
<bofh> processing time :P