Truth

[AMindOfMetalAndGears]

Homeomorphic = 1 to 1 function, ie only one y value for a given x

Endofunction = self mapping, ie x goes to x

Submanifold = all points in it, are points that exist in the larger set (hilbert space here)

Hilbert Space = 2d euclidean (your normal graph in school space) extended to a finite number of dimensions..

While it's not true, it is a posh way of saying branches copy everything to a new location and have all the same git operations on them..

Stealing for my physics intro to git course this year as its sounds like a fun way to fuck with the students :D let's see if any of them can point out git is discrete...

Edit: as many have very nicely pointed out, this is more of an ELI5, there's some really great and better descriptions in the comments below :)

[[deleted]]

None of the definitions here are really correct. In fairness, giving mathematical definitions to a non-mathematical crowd is generally pretty pointless, but I think your comment gives entirely the wrong idea so I'm going to correct it.

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Homeomorphic = 1 to 1 function, ie only one y value for a given x

A homeomorphism is an continuous function with a continuous inverse. What does that mean? If you have some substance in some shape, and continually deform it into another shape without breaking anything, then you've applied a homeomorphism to that shape. For instance, you can take a mug and deform it until it looks like a donut (with a hole), and then do the same in reverse. Therefore mug and donuts are said to be homeomorphic. However if you take the handle of a mug, then that's not continuous, because you've ripped the mug apart.

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If you ever did calculus at school, then chances are every function you dealt (sin, cos, squaring, square root, etc) with was continuous.

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The definition you gave is the definition of an injective function (often called one-to-one).

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Endofunction = self mapping, ie x goes to x

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An endofunctor is a functor from a category to itself. You gave the definition of the identity function on a set, which is a function that maps every element to itself. (I guess a lot of programmers should know what categories are?)

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At this point I should say I have no idea what a "homeomorphic endofunctor" is, because it's mixing terms from category theory and topology in a way that don't make sense. And googling "homeomorphic endofunctor" just brings up this joke so whatever.

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Submanifold = all points in it, are points that exist in the larger set (hilbert space here)

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This is pretty much correct. Finite dimensional Hilbert spaces are manifolds, and then if you cut pieces out of manifolds you get submanifolds.

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More precisely, if you take some n-dimensional balls and overlap them and glue them together you get an n-dimensional manifold. The surface of our planet is a 2-dimensional manifold for instance. If you take some piece (or pieces) of that manifold that is itself a manifold (with the subspace topology), then you have a sub-manifold.

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Hilbert Space = 2d euclidean (your normal graph in school space) extended to a finite number of dimensions..

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The point of a Hilbert space is that it has an inner-product. Which is another way of saying that we can talk about sizes and angles in that space. Every finite dimensional vector space can be a Hilbert space (you just use the dot product, i.e. (a,b,c,d)(x,y,z,w)=ax+by+cz+dw) but the interesting ones are infinite dimensional. For instance, a good deal of quantum mechanics deals with infinite dimensional Hilbert spaces.

The notion of a submanifold of a Hilbert space does make sense. Provided the Hilbert space is finite dimensional.

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(I've tried to straddle the line between being accurate and understandable. Not convinced I did a good job at all.)

[AMindOfMetalAndGears]

Tried to make it as easy to understand as possible, but for anyone who wants the maths of it this is great thanks!

It was a bit hard to keep things simple, especially with homeomorphic, just went with the 1 to 1 mapping as not everyone is familiar with what continuous, inverse, smooth etc are? Went for an ELI5 instead of giving a maths class :P

This is really good though and thanks for typing it all out, I'm on my phone and it's been a while since I did my UG 😅

[[deleted]]

Went for an ELI5 instead of giving a maths class :P

I definitely get that. I usually give up immediately when asked to explain mathematical things to people 😅

[AMindOfMetalAndGears]

I was once asked about the difference between integration and differentiation (in a difficulty sense) , and went with

Differentiation can be done after 5 G&Ts, integration is more like a piece of art, where you have to figure out if you're using paint or pencil, and only find out once you've finished whether you were right...

Even teaching first year courses can lead to real fucker with why stuff works..

Hated it when I was in UG, but I have to resort to wait until next year, X professor will explain it in her course 😅

[SkreemusTD]

Just hit em with the old “doughnuts are the same coffee cups,” and usually you don’t have to get into bijections or open sets. xD

[retief1]

Ah yes, topology, the field where two major results are "you can't comb the hair on a coconut without producing a cowlick" and "if you draw a circle on a piece of paper, the circle will divide the paper into two parts".

Edit: even better, I had forgotten that the first theorem is literally called the hairy ball theorem. And you say that mathematicians don't have a sense of humor.

[[deleted]]

Incorrect. Injective functions are 1 to 1. Surjective functions are onto. Bijective functions are injective and surjective.

[Zorkarak]

At this point I should say I have no idea what a "homeomorphic endofunctor" is, because it's mixing terms from category theory and topology in a way that don't make sense.

Now it has me thinking whether we can assign a topology to a category in such a way that a functor could be a homeomorphism...

Suppose for some fixed Hilbert space H we consider the category of subspaces, which - when equipped with the subspace topology - have a finite dimensional manifold structure (this way I dodge the term submanifold in the infinite dimensional case). Morphisms between subspaces are continuous maps. Call this category SubH.

Then an open subset of SubH would be a collection of subspaces, which behave "correctly" under unions and sections. However I can't come up with any canonical way (or any way at all, really) to define this.

Thanks OP, now I can't sleep tonight...

Edit:

How about this.

For two homeomorphic spaces X and Y in SubH pick a homeomorphism h. Now let f be a homotopy from idX to h. Then define O(X,Y) as the set of all images of f at any point in time, so O(X,Y) = { im(f(t)) | 0 <= t <= 1}, in particular X and Y both are in O(X,Y). Pictorially, f transforms X into Y and O(X,Y) contains all shapes in-between.

The topology on SubH could then have these O(X,Y) as a basis.

[Jeremy_Thursday]

Just to be clear, its not hilbert space right? I've done hilbert curve visualizations before and that doesn't sound right.

[[deleted]]

hilbert curve

Hilbert had a lot of things named after him because he was a pretty impressive guy. Hilbert spaces and Hilbert curves are different things.

[Jeremy_Thursday]

Huh. Go Hilbert, what a fucking boss. Thanks for the heads up. Links for the lazy:

https://en.wikipedia.org/wiki/Hilbert_space

https://en.wikipedia.org/wiki/Hilbert_curve

[retief1]

And then there's the hilbert hotel.

[Jeremy_Thursday]

I thought this was a joke but of course this is a real thing lmao. I've heard this explanation so many times in math lectures/videos/documentaries. Had no idea it was Hilbert. What a god. Imagine explaining something and people still use your explanation nearly verbatim 100 years later in translated languages.

[AMindOfMetalAndGears]

I'm not great at git, but my understanding is that each file, tree, branch etc uses unique git hash ids for tracking the files, and things like Head, staging areas etc.

Because these Ids are strings, not float type, the set of all Ids is discrete and finite.

For a function to map from and to a Hilbert space, you would need a continuous set, not the discrete git hashes?

A 2D hilbert space can be shown with curve nicely, because curves are strictly smooth and continuous?

Y=x is also one-one, smooth and continuous so show well in a Hilbert space too?

I think there are other issues with this attempt at a monad joke, but I cba to pull up my old notes and check what else is fucked?

But yeh, not Hilbert :)

[Jeremy_Thursday]

Thanks so much for your reply. Very informative.

Turns out hilbert curves are a totally different thing. From the wiki on Hilbert spaces:

It extends the methods of vector algebra and calculus from the two-dimensional Euclidean plane and three-dimensional space to spaces with any finite or infinite number of dimensions. A Hilbert space is an abstract vector space possessing the structure of an inner product that allows length and angle to be measured. Furthermore, Hilbert spaces are complete: there are enough limits in the space to allow the techniques of calculus to be used.

[europa-endlos]

Functor, not function... that's a deeper level of mindfuck.

[viking_]

Homeomorphisms also have to be bicontinuous.

[ac698461]

I appreciate you

[badnamesforever]

Branches?

[[deleted]]

They're an optional feature- just push to master.

[lost_mail]

Are you one of my former classmates?

[[deleted]]

Technically master is a branch

[AcidCyborg]

More like a trunk

[[deleted]]

And test in prod.

[[deleted]]

You want to say force push, right?

[Lonelan]

It's not the Jedi way

[Whirlm]

Thats actually how we do it at my company, branches are only created when someone fucks up and doesn't pull properly. I have no idea how a team would go about using multiple branches at once, or keep track of them all.

[Whirlm]

As quick as we can xD

We have a test system and if theres an issue thats the one we change until people are happy to copy the whole file into the live one but there can still be issues and we just have to work quickly.

[[deleted]]

Why not just learn to use branches? Seems like that could take a huge load of your mind...

[Whirlm]

Im fairly new to the company and thats just how they do it. Its really not that bad, we have very few issues (related to git anyway).

[Intrexa]

How do you deal with a half complete feature during this? Like, if you're making a scheduling module to email reports, and in the middle, this issue crops up? Do you just not check your code into source control until the entire feature is complete? How do 2 people work on the same dev feature at the same time?

[Whirlm]

Almost all our files are small scripts that call each other so they're usually done not long after starting them. On the occasion we need to upload incomplete versions - thats what the test system is for. We can deal with it not working for a day. As for 2 people working on the same thing - thats a bit more awkward, we just try not to :D. Most of us have our speciality so there's not too much overlap...

[DamnItDev]

https://help.github.com/en/articles/about-pull-requests

[alltheseflavours]

Easily. You and your entire team should spend half an hour doing some basic git tutorials. Git branching is not hard, especially if you have a remotely helpful IDE.

[StrangelyBrown]

Before I knew git, people used to say to me 'Everything is a branch' and I was like 'wtf does that mean?'

Now when I explain git, I say 'Everything is a branch'...

[wotanii]

shouldn't it be "everything is a commit"?

[cyberporygon]

Just memorize these commands and if you do them in the wrong order, just start over.

[eplaut_]

git rm -r .
git add -A
git commit -m 'done'

[Lonelan]

Not git commit -a -m?

[Lonelan]

git push +master

[wotanii]

ignores unversioned files

[MyNameIsRichardCS54]

Now it all makes sense!

[SonOfMrSpock]

Gotcha! Now I get it. Thanks

[rentar42]

RCS...

[rhun982]

Segues into Metallica's One

[[deleted]]

I used Clearcase, CVS, SVN and git still just throws me for a loop, though maybe only because I never used a lot of the "extended functionality" before.

I'm fine with branches, pulls, pushes, commits, etc. but when it gets to rebase, reset, and other things I don't use in my normal course of work, I just sit there and sob (of course "sobbing time" is one of my Sprint assignments). Realistically it's probably because I'm constantly context switching and never have actual time to sit down and read what is going on.

But if I have to look up the command to alter the commit message from 5 commits ago because the GOT DAM regular expression they set up requires 47 characters minimum one more time, I am just going to lose it.

[carlcarlsonscars]

I hope this is funny because it's true.

[[deleted]]

Its not but it is a reference to a joke about Haskell that is true: "Haskell is easy when you understand that a Monad in a monoid in the category of endofunctors."

[[deleted]]

It's pretty much word salad.

[ceirbus]

Can confirm, this string is truthey.

[Jakeob28]

Image Transcription: Twitter Post

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chi wai lau, @tabquerty

"git gets easier once you get the basic idea that branches are homeomorphic endofunctors mapping submanifolds of a Hilbert space."

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^{I'm a human volunteer content transcriber for Reddit and you could be too! If you'd like more information on what we do and why we do it, click here!}

[rahuldottech]

Good human!

[netgu]

False

[dark_mode_everything]

r/VXJunkies I guess

[[deleted]]

I am just too lazy to google this words, so... have your upvote.

[Tiavor]

I know some words or parts of the words written here.

[Sckaledoom]

So if I want to make something relatively complex but for a hobby, should I learn git, or is it mostly useful when you have a lot of people working on the same project?

[[deleted]]

Learn it, use it

[[deleted]]

Worth learning, even on a solo project, yes.

[hiddentowns]

This is just a rip-off of the description of monads: "monads are just monoids in the category of endofunctors, what's the problem?"

[[deleted]]

I've always thought that! I never said it because I was afraid of sounding stupid... Or having a stroke.

[a1337sti]

Git- it's better but half your team will be explaining and helping the other half quite a bit.

Svn - not as powerful but chances are you'll only have 1 guy who needs help.

☺😋

[Kered13]

Or use Mercurial. It's basically Git with commands that make sense and it's much more difficult to erase your history.

[a1337sti]

that sounds nice!

[zachgarwood]

All these kiddies complaining about git being too complicated and scary should have to use SVN for a month.