Rabbits Rabbits Rabbits
Reblog this on the first of the month for good luck all month long!

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@compositionalotterfolk
Rabbits Rabbits Rabbits
Reblog this on the first of the month for good luck all month long!
sanest mathematician you know: we need to teach children about groups
I’m ashamed, but I’ve unironically said this before.
Have you ever wondered what a "half composition" of a function would be?
If we say a function "f" is composed with itself "k" times, we can intuitively interpret that as f∘f∘...k times (ie, the kth composition of f), so long as k is an integer; but what about when k isn't an integer?
We could interpret the "a/b th composition of f," as some function "g", such that, when g is composed "b" times with itself, it is equal to f composed "a" times with itself. While this interpretation is sound it still begs a few questions: is there an intuitive way to think of "real" compositions, what about complex?
These questions are interesting, however, I feel they are dwarfed by one you could be considering right now:
If we have some smooth function f, can we find functions that are these "exotic composites" of f? Can we do so for any smooth function?
Recommended preliminaries:
A good understanding of taylor expansions is very necessary.
Familiarity with ODEs would be helpful, but they are not used directly.
One issue here I can see is that you assume that if you have a formula for f*s(x_f) and its derivatives at integer values of s that can be extended to the reals, that it does extend to the reals. Unless you prove continuity with respect to s the non integer values could be unrelated to the integer values. Assuming you do (you probably can), you need to prove that f*s(x_f) is analytic as a function of s (you cannot prove this by the formula for integer values being analytic when extended to reals) in order to say that the analytic continuation of the integer values is equal to the true function.
You probably can do so, but you’re missing important details.
I left out the details on the first point because I thought it might be unnecessary, but the proof does seem incomplete without it:
Let’s consider a point “p” in A a very small distance “r” away from the fix point. Now, if we apply f to p and x_f, x_f clearly does not move, however f(p) is not p, ie it “moves.” The real question is “by how much?” That is totally dependent on the distance r. As we let the distance r grow very small, it is clear that this point p is moved closer to x_f+f’(x_f)r. This is because our first order Taylor expansion about x_f is: x_f-(x-x_f)f’(x_f). This kinda feel like where not actually getting anywhere, but the point is if we substitute this approximation into itself repeatedly we at first can say we seem to get x_f-(x-x_f)[f’(x_f)]^s. Now why is this any better evidence? For linear functions, composition can already be extended, and in exactly this fashion (you can check from here that the homomorphism is held, which does mean that the expression is valid; but uniqueness is uncertain).
The proof that I placed up there is essentially the veiled version of this logic: composing an approximation with certain properties with itself that are certainly preserved.
Tbh, I thought the second point didn’t have much merit, however, I double checked and, it is very important to consider. The entire formulation does not explicitly reference the differentiability of f*s(x) with respect to s anywhere, and almost none of the intermediate steps actually require analyticity in terms of s, only that f*s(x) exists. That is, all but commuting the forward operator and the differentiation operator.
The quickest proof that the forward operator and derivative commute uses the identity e^{partial_s}=T_s, which clearly commutes with other partial derivatives, unless the chosen function is not smooth.
But I do think that this is the only point of issue, as nothing else obviously requires f*s(x) be analytic in terms of s, it all more acts as a proof that it must be (which can be see via and inductive argument).
I think this might be due to a uniqueness issue. If we assume f*s(x) must be analytic, the formulation continues without issue and leads to a result without obvious contradiction. This result should have all the desired properties regardless of the fact that it was constrained. It is possible that there is an f*s(x) that is not analytic, but those answers are not considered.
I think the point you were trying to make was slightly different, but it’s all about deciding what versions of our function we are considering. I should probably prove that a valid analytic function exists; but that’ll take me more time. I might post it later.
If this doesn’t seem like enough, or if anyone wants to take a stab at the proof just lmk!
Have you ever wondered what a "half composition" of a function would be?
If we say a function "f" is composed with itself "k" times, we can intuitively interpret that as f∘f∘...k times (ie, the kth composition of f), so long as k is an integer; but what about when k isn't an integer?
We could interpret the "a/b th composition of f," as some function "g", such that, when g is composed "b" times with itself, it is equal to f composed "a" times with itself. While this interpretation is sound it still begs a few questions: is there an intuitive way to think of "real" compositions, what about complex?
These questions are interesting, however, I feel they are dwarfed by one you could be considering right now:
If we have some smooth function f, can we find functions that are these "exotic composites" of f? Can we do so for any smooth function?
Recommended preliminaries:
A good understanding of taylor expansions is very necessary.
Familiarity with ODEs would be helpful, but they are not used directly.
Extension of the Fibonacci #s via Composition of Functions
There are plenty of ways to derive the extension of the Fibonacci numbers to the reals. But one way is a personal favorite for me.
I have a few questions if you don't mind.
So from the action of (1) and following to (5) should not that matrix be ((1 1), (1 0)), since acting F on the vector in (1), one would want the x1 to carry over. Though I may be misunderstanding how you arrived at that matrix.
Either way, I was able to reproduce the very left hand matrix in (6), but I have the columns swapped. I'm pretty sure that's because of the differing matrices, I continued on with the one I mentioned before.
But so from there, deriving the very right hand matrix in (6), I'm not entirely sure how you derived it if not from the shortcut for getting the inverse of a 2x2 or row reduction. I assume some of my confusion stems from some trickery of the golden ratio, always able to rewrite it into slightly more convenient forms, but regardless of that, it looks as if you calculated the determinant of the left hand matrix to be 2+phi, but I calculated 1-2phi. Well, really I got 2phi-1, but due to the column swapping I know it differs by a minus sign.
But so 1-2phi is sqrt5, which is what you have in the denominator in (7), which is not equal to 2+phi, so I don't know if I'm misunderstanding something or there was a typo at some point or something. At the end, using your matrix for F in (5) I got the same as your (7), if I understand the result is basically just the upper right hand of the matrix representing the Jacobian of Fs? So as far as checking your matric calculator, checked!
But using the different matrix that I suggested I have basically the same thing, but a minus sign on the second term, so [phi^s-(-phi)^(-s)]/sqrt5.
I was curious, so I plotted these, at lest the best a real number plotter would do with that -phi, and both your solution and the one I got lie on the curves for cosh(s*ln(phi)) and sinh(s*ln(phi)) That makes sense of course since that essentially looks like both solutions, just depending on the fractional representation of whatever decimal is being input for s.
I guess I really only ended up having the one question to ask about how you arrived at your matrix representation for JF. Anyway, I hope I'm not being too forward in typing all this, this is a really fun problem to think through!
I looked at the photo of the blackboard I did this on and I totally got the Jacobian flipped when translating it over in (5) ;-; and I straight up am inncorrect in (7) T_T.
Regardless my work that reaches (6) uses the correct matrix, so if yours is different I would have to imagine that either I made a mistake or that when you made your Eigendecomposition, you chose different columns to have the chosen eigenvalues.
Also in (6) to invert the matrix I augmented it with the identity matrix and did row operations (I had limited internet and don’t generally memorize shortcuts), and then I simplified (using golden ratio magic) till I thought it looked good enough. I think in the process of simplifying I lost a ^{-1} exponent in the numerator of the top right entry of the far right matrix.
For (7), the known closed form solution is a difference in the numerator (which you have), and I don’t have access to the program that I made do my algebra, but I remember at least trying to check it.
In future I will not be posting math at; I think it was ~1:00?
Thanks for catching me, working with actual examples is a weakness of mine.
Item: A Thought Bubble Rarity: ✦ Uncommon
Has a game ever genuinely changed how you think about something?
Feed your dashboard by answering my question, blogger.
I used to play factory sims, primarily satisfactory. While I think the game is wonderful, I didn’t like it (I want it clear that I think it’s a good game, not my cup of tea). But I would play it anyway. I would put hours into that game, and I felt each hour was wasted. After so many hours is when I realized that if I’m not having fun, that isn’t an absence of some QoL feature, that means I shouldn’t be playing the game.
That kind of started a wave (or perhaps was caused by some wave) of me realizing that I should do what I enjoy. It was such a bizarre thought: that I was allowed to enjoy myself. I even still wonder why I ever thought otherwise, or why it often feels like this thought still looms over me.
I’m pretty much over playing games I don’t enjoy, but I’ve found it leads to me to play games very little, and I think it’s just a little sad in that sense.
Don’t Drink Water!
Water is actually super dangerous, consider the facts! (NOT PROFESSIONAL ADVICE)
Extension of the Fibonacci #s via Composition of Functions
There are plenty of ways to derive the extension of the Fibonacci numbers to the reals. But one way is a personal favorite for me.
Which math is your favorite
I don’t know all that much math, the highest level course I’ve formally taken so far was an ODE course, but my school doesn’t have anything higher so I’m just getting credits for subjects I already know this semester.
I’ve been reading analysis books, and I think it is the favorite so far (subject to change). I feel a bit out of depth, but I think I’m getting enough out of it anyway.
I haven’t interacted with much else. I tried to look into some topology but the book I got was very boring. I’ve been reading a lot more, so If anyone has any (math) book recommendations I’d love to hear them.
so I got into grad school today with my shitty 2.8 gpa and the moral of the story is reblog those good luck posts for the love of god
okay so i just got my dream job??? a week after applying to it?? and now i’m thinking….maybe this is the good luck post
…..not even six hours later i got an offer of a well paying full time long-term job with free room and board in queens in nyc, allowing me independence and a way to escape an abusive situation and an unhealthy environment
likes charge reblogs cast, folks, this is the good luck post
i need all the help i can get for finals
Hey so
the last time I reblogged this post right before I got a great job, in a permanent work-from-home position, with benefits, retirement, and a salary literally 3x what I was making before, doing something I really like.
So you know.
This might be the real one, y’all.
what the hell? i could use some luck *hits reblog*
World Heritage Post
reblogging again… need it bad lol
*hits reblog* please I need the luck
Here's a fun little math puzzle, not too hard. Classify all mereomorphic functions f such that for some point p f misses p except possibly at p in which case f(p)=p
I gave it a go bc I’ve been studying complex analysis and I’m not all that confident (please let me know if I made mistakes):
I’m assuming “misses p” means there dne t in C that is not equal to p such that f(t)=p. With that definition we can state f(z)=p is a condition we disallow.
Since p is technically an entire function f(z)-p is meromorphic. Any meromorphic function can be expressed as a ratio of entire functions, which in turn, may be factored using the Weirstreiss factorization theorem. If the function in the numerator has a root f(z)-p must have a root thus breaking the condition. Skipping a few steps using the weirstreiss factorization, we should be able to reach f(z)=p+(1/g(z)), where g is an entire function.
If we want to specifically make the exception for p to be a fix point of f, it is first necessary that g does not have a root at p and second we must have some factor that goes to zero in the numerator iff z=p. f(z)=p+(z/p - 1)^m / g(z), should be sufficient, assuming m is a natural number (including zero) and g is an entire function without a root at p.
I stand in the wind and I let the moments wash over me. Cold and biting, hiding me from my own warmth.
As I stand dormant, my emotions are greying. Resigned to my torment, I feel I’m fraying.
I seek no shelter, there is none that I see, spare the grass that stands here with me. It’s insufficient— I’m insufficient, insufficient to stand in this field.
I will die in this field, proving just that.
A few months ago I was playing Minecraft in hardcore mode. At the time my headset was broken, right in half, simply due to repetitive stress, but it was broken nonetheless. Thus I was playing Minecraft in utter silence (naturally in the middle of the night). At some point around gaining access to diamond tools and low level enchants, I spent a night mining, notably close enough to the surface for mobs to spawn on the surface. I say all of this to preface my death to a creeper. While the notion is simple the experience was outlandish. With no noise, no feedback I was dead; one moment alive another gone. The incredulity and astonishment I experienced was so intense, that the moment seemed to extend, stretching time, deprived from all sensation except for the message of my own death. I think I learned something about how it is like to die because of that experience; with one moment extending for what seems a lifetime, wondering how this could have come to be, failing to understand what action has deprived you from interacting with the world any longer. Of course, I see this as just one way to die, I’ve had other experiences that I expect death to feel like, but I also wonder what gives me such certainty in such an uncertain subject
Afterwards I was really annoyed bc I had just started building a really cute pink house on a cherry blossom mountain, and now I couldn’t even finish it.