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05:01
I have a hard time to answer this question, any help math.stackexchange.com/questions/2173711/…
What is known about the multiplicative order of matrices over finite fields?
can you be more specific?
In particular I'm most interested in the Galois field with 2 elements, binary matrices
But I'm very interested in the Galois field with general prime order
The matrices in question are square
And the order can be assumed to be too large to feasibly search numerically
Er.. when I say "multiplicative order" I'm generalizing the notion to matrices, what I exactly mean to find is the period of the function $f(k) = \mathbf{A}^k$ where $\mathbf{A}$ is the matrix, and $k$ is an integer exponent
Over $\text{GF}(p)$ it's clearly less than or equal to $p^{n^2}$ for an $n\times n$ matrix, but that bound is pretty useless to me :/
Since it's uniformly random, I can even make some guesses about the cycle length, but I'm pretty stumped on finding an exact result
05:38
Analyze matrices in normal form to see what kind of orders they can have.
Thanks, I'll try this approach
Is there a specific normal form you'd suggest?
is there a way to define wedge^n without referencing bases?
Hey
hey
like referencing alternating forms like seems to lock in a basis
An orthogonal basis of a subspace is a basis $S$ in which for every $u,v \in S$, $(u|v) = 0$ ?
$(u|v)$ being dot product
05:50
no. (u*u) > 0 for u != 0
and 0 is not an element of a basis. So your condition is slightly wrong
otherwise yes
@YashFarooqui "the vector space of alternating n-ary forms" does not "lock in a basis"
doesn't it? is there a basis independent defintion of alternating forms?
$f(v,w)=-f(w,v)$ (for binary) for example
that's not basis independent though
05:59
?
like
V^k -> F right?
it makes no reference at all to any choice of basis
that's what a form is
sure, V^k->F
fine, it may be "basis-independent" but it still has indexing on V^2 that is not geometrically natural
there are no coordinates involved
06:00
is what I mean
I don't know what you mean
"indexing on V^2"?
v \in V and w \in V in your example
V^2 is also a vector space in its own right though
not just the product of two vector spaces
a multilinear form V^k->F does not care about the vector space structure on V^k, it's really a linear map V^\otimes k ->F
(the kth tensor power)
I still don't see your point
there are no coordinates anywhere
there is "first vector, second vector, third vector, ..." but that's not a choice of coordinates with respect to which we are representing the vectors
06:02
why isn't it?
um, why would it be
So there's no geometric meaning to alternating forms?
didn't say that
that's good to know
no geometric meaning wrt V^k
if alternating k form?
huh?
oh, you mean the componentwise addition in V^k? no, not relevant to k-ary forms.
a k-ary form is not a linear map V^k->F.
06:04
you're right. I think I see. The structure of k-linearity puts more structure than just linearity
?
A form is a k-linear map from V \otimes k to F?
I am using k as a natural number
oh less structure
yes
I don't see what you mean. Linear in each "coordinate"
A k-form is a map V^k->F which is linear in each individual argument when the others are held constant. That's how multilinearity works. It's equivalent to specifying a linear map V^{\otimes k}->F.
06:06
yeah
I was using k-linear to mean
bilinear when k = 2
trilinear when k = 3
etc.
okay same page, just different terms
but anyways I think I get it. the reason that there's no "basis-independent" definiton is because thinking of a form as a map V^k -> F is entirely the wrong way of looking at it
it is basis-independent
you seem to be confusing basis for V^k (which is irrelevant since we're not talking about a linear map from V^k) and basis for V
using the quotes to indicate what I was using as terminology
implying that it is incorrect terminology
that's a very confusing way to have a conversation.
@arctictern @Semiclassical hi
I apologize for speaking in a confusing way.

Anyways I think I got it. Thanks arctic tern!
06:44
I think I made a nice dent in the problem: When $\mathbf{A}$ is a binary $n\times n$ matrix, the least exponent $k$ which takes $\mathbf{A}^k$ to the identity matrix must divide $\sqrt{2^{n^2-n}} \prod_{i=1}^n (2^i - 1)$
That's pretty much already enough to make a reasonable computer search
07:42
@sequence see in Wikipedia Divisor function. Then see the case $\alpha=0$, that is $\tau(n)=\sigma_0(n)$, a notation for the number of divisors of an integer $n>1$, where $\tau(1)=1$, and for example since $1,2,3,$ and $6$ are the divisors of $6$ then $\tau(6)=\sigma_0(6)=4$. See your case $\alpha=0$ in the section Series relations. Is not required a response of this comment, good luck.
Good morning all users, bye.
For some reason now linear algebra is starting to make sense for me, like out of nowhere now I can see the relations
For some reason now linear algebra is starting to make sense for me, like out of nowhere now I can see the relations
@Maks por ejemplo?
Puedo deducir cosas tipo dimensiones, porque la dimension de la suma de subespacios es la dimension de la interseccion + dim de la suma
O porque el rango + nulidad de una transformacion lineal es la dimension de V
Otras cosas sobre la base dual, como la existencia y unicidad
O porque si una transformacion es isomorfica entonces su nucleo es {0}
cosas simples pero antes no podia deducir de donde salian
buenas suertes cuando tentas de usar la intuicion para dimensiones 4+
08:01
Porque la intuicion ?
@Maks never mind
thanks for the input @arctictern
08:19
I've got a program that determines the exact order of an 80x80 in about 1 minute now :)
08:36
Hello!!

I want to find the rank of the matrix $\begin{pmatrix}0&1&1\\ 0&0&1\\ 0&0&0\end{pmatrix}$, but I am not really sure what to do in this case where the first element is zero. Could you give me a hint?
I think it is 2
@DHMO How did you find it?
@MaryStar because it has 2 linearly independent vectors
Ah, so we don't have to do anything for example using Gauss or something else, right? So, it is not a problem that it starts from zero, is it? @DHMO
right
08:47
@DHMO Ok. Thank you!!
09:25
We have the tableau $\begin{pmatrix}
\left.\begin{matrix}
1 & 0 & \alpha \\
0 & 1 & \beta \\
0 & 0 & 0
\end{matrix}\right|\begin{matrix}
c\\
d\\
0
\end{matrix}
\end{pmatrix}$

Since there is a zero-row, do we conclude that the column vectors are linearly dependent? Or to check the linearly (in)dependence of the column vectors do we have to check if there is a zero-column?
Do you have an idea? @DHMO
@MaryStar the former
A lot of things in my brain are tree dimensional (and no I have not made a typo, but perhaps I used imprecise language)
@Secret so make it more precise
Ah ok... The number of linearly independent row- and column vectors is the same. And from the tableau we get that there are 2 linearly independent row- and column vectors, or not? Therefore the dimension of the the vector space spanned by the solumn vectors is $2$, right? And this is also equal to the rank of the matrix, right? @DHMO
My brain thinks like a tree where every node give a random number of branches. Therefore, messy brain
09:38
@Secret for example?
@MaryStar yes
e.g. Doing some calculus exercise, and then suddenly I think about vector spaces because a multivariable function has 4 entries, which reminded me of 4 dimensions, which then remind me of R^4
@Secret I see
Do we also that the dimension of the solution space is equal to the numer of free variables? @DHMO
@MaryStar I think so
Therefore, it is $1$, or not? @DHMO
09:42
I think so
What is a geometric interpretation of all these information? Do we get that two column vectors are either a multiple of each other or they are on the same line? Or is there also an other interpretation? @DHMO
Ich habe keine Ahnung
Entschul.
Kein problem
10:05
Claim:
> As scary as it sounds, Daily Routine is suspected to have countably infinite number of parameters, since the procedural nature of Daily Routine means the nodes occur in discrete numbers thus there exist a bijective mapping of them to the natural numbers
Background context: Consider Daily Routine to have some kind of digraph structure
meanwhile:
12
Q: Can there exist an uncountable planar graph?

Joshua PepperI'm currently revising a course on graph theory that I took earlier this year. While thinking about planar graphs, I noticed that a finite planar graph corresponds to a (finite) polygonisation of the Euclidean plane (or whichever surface you're working with). By considering, for example a full t...

Lol. I just happened to demonstrate another example of how random my brain is when it comes to connect things
32
Q: What is the difference between discrete data and continuous data?

AlbortWhat is the difference between discrete data and continuous data?

Search for that because I initially think "discrete number" is ambigurious
Therefore in summary: My brain=Given a proposition, which each word or each phrase is considered a node. There is nonzero probability that a random number of branches follow for each node. This process can be repeated indefinitely with nonzero probability
What is the englisg word for "gluing" solutions of a differential equation ?
or "recollement" in french.
10:28
I only found "Adjunction space" for recollement in the context of topology, not sure about differential equations unless the solution space is equipped with a topology
no it is just joining or gluing the solutions at a point x0 so that the joining have some requested regularity. usually I use wikipedia to find this, but I can't seem to find the wording this time.
you might be looking for the term "Boundary conditions"
10:47
I've just obtained the prime factors of a 19728 digit integer :3
Or concretely, 10x the length of a paranoid RSA key
(the number is actually $2^{256}$-smooth *(actually actually (2^{217}$, to be exact), so it's not groundbreaking, but it sure feels good since it's for an app)
but what is the number of digits of the smallest factor ?
the smallest factor is $2$ and the largest factor is $160619474372352289412737508720216839225805656328990879953332340439$, the rest look Poisson distributed
(588 unique factors)
if it has that many small factors, it is not really RSA safe.
@user90369 many thanks for your feedback, I didn't know such question from the literature but now with your feedback I have more idea. Many thanks then for your attention and help.
@pilko I just said above it's $2^{217}$-smooth.
or I guess some people call that concept "$B$-friable" instead of "$B$-smooth"
the reason I compared it to an RSA key was to illustrate why I couldn't just throw usual methods at it
10:58
oh, ok.
but I could analytically factor it down enough to get ECM to chug it out in the end
Hi @robjohn how's it going?
BTW since many people joined the chat, any answer to my question around 11:28 ?
11:42
0
Q: Normal distribution restricted to a specific interval expression.

user8469759Let $X \sim \mathcal{N}(\mu,\sigma)$, i.e. $X$ is a random variable with distribution $$ p_X(x) = \frac{1}{\sqrt{2\pi}\sigma} e^{-\left(\frac{x-\mu}{\sqrt{2}\sigma}\right)^2} $$ I haven't touched probability theory for a while it is then possible I'm mistaking something. I want to find the dist...

 
2 hours later…
13:20
@skillpatrol pretty good, but very busy. How are you doing?
13:35
How do bounties work?
God damnit! I just ran a numerical solver for two and a half hours... forgot to save the result to a file, just printed it out to the terminal
14:04
hi chat
@MickLH Ugh, that sucks.
@MickLH Did you have the settings etc. saved at least, so that you could immediately re-run it?
14:25
If I reply to the message of a non-pingable user, will the user be pinged?
14:39
if $F(x,t): S^1 \times [0,1] \longrightarrow S^1$ is a cts function is $\frac{F(x,t)}{|F(x,t)|}$ the identity?
$S^1$ is the circle in $\mathbb{R}^2$
@DHMO if you want you can reply to a message I wrote in the chat of TeX stack exchange a few months ago to find out, I should no longer be pingable
however if I go to look for that message I might log into the chat :)
@s.harp replied
Just got pinged
:o
this is creepy
although can you ping me normally?
14:44
but you are still not pingable
so maybe I am pingable
ah k
@Riemann-bitcoin. the identity of what?
sorry of $f:S^1 \longrightarrow S^1$
@AlessandroCodenotti buongiorno
If $F$ maps into $S^1$ wouldn't $|F|=1$?
14:47
How's $f$ defined?
Hi @DHMO
@AlessandroCodenotti Sto cercando per una intuizione di insiemi aperti
f is arbitrary (from $S^1$ to $S^1) I am trying to show that $S^1$ is not simply connected by assuming it is nullhomotopic then out of the homotopy deriving a contradiction from the fact that I made a homotopy from the identity on f to the constant function.
@DHMO those containing a nbhd of their points
Again, if $f$ maps into $S^1$ then wouldn't you always have $|f|=1$?
Besides, the identity is a function $S^1\to S^1$, not a function $S^1\times[0,1]\to S^1$
14:51
Oh I see ...
@AlessandroCodenotti entonces cual es una intuicion del entorno?
Porque los conjuntos abiertos son todos entornos del elemento
that does not work I need to do something else thank you
por ejemplo, (0,1) U (100,101) es tambien un entorno de 0.5
aunque 101 es muy lejos de 0.5
just taking f=id we get the contradiction
@AlessandroCodenotti piensas que puedes entender espanol hablado en lugar de espanol escrito?
14:56
Not really
eso es muy interesante....
@DHMO an open set containing the point, which sounds kinda circular...
@AlessandroCodenotti pero se supone que "entorno" de un punto es muy cerca del punto
funny how the italian you're talking to is speaking english instead of italian :P
@BalarkaSen and i'm speaking spanish to him
15:01
sure
Seems like a pretty good way to practice language skills, actually.
@Semiclassical yes, but some people here don't like it
@BalarkaSen do we have a name for this particular topology on S: $\tau = \{\{x | x < s\} | s \in S\}$
talking other language should be fine in the chat. not sure why people won't like it
Well, it can feel a bit spammy if you can't actually understand it.
But ehhh.
@DHMO You mean S is ordered?
15:05
@BalarkaSen yes
@Semiclassical or they're jealous :p
well in the physics chatroom they seem to be quite strict on this
the reason being the mods can't modulate what you say if you're speaking in another language
Yeah.
At the same time, if you can't understand what someone is saying it's hard to get offended by it.
@BalarkaSen i can't write Spanish and I'm more used to talk about math in English so I just answer in English :P
Give me an example of a open set containing a point x in the usual topology that is not a neighbourhood of x?
@AlessandroCodenotti you can write in Italian
@Secret an open set by definition is a neighbourhood
@DHMO I think this is called the right order topology
15:09
But aren't neighborhoods must contain some open sets that contains the point x?
@Secret in that case the open set is the neighbourhood itself
@AlessandroCodenotti Fair enough.
@AlessandroCodenotti o grazie
Going by that, I think it'd be the left order topology
what's an intuition of a neighbourhood?
15:13
It's pretty big
goes all the way to the right/left
@BalarkaSen is that a reply to me?
@Semiclassical woops, well the names make sense if you think of a total order as a straight line
@Secret here's my current (flawed) understanding: an open set is such that it is (contains) a neighbourhood of every point; a neighbourhood is which contains an open set containing that point...
Just had another AT lecture, we discussed properties of fundamental groups, the homomorphism induced by a continuous map, they're preserved by homotopy equivalences ans homeomorphisms, stuff like that. It's funny how much we can say even without knowing how to compute any of them
@Semiclassical wasn't it left?
15:19
...
(I'm very sorry for the message above)
@AlessandroCodenotti the intuition of nearness still isn't working...
Well here's a counterexample:

{{},{a,b,c},{a,b}}

{a,b} is open but it does not contain a neighborhood of c, which is {a,b,c}
I knew I should've said "correct" :P
@Secret {a,b} contains a neighbourhood of a and b
I meant "a neighbourhood of every point [in the set]"
15:22
@DHMO but the neighborhood of a and b is {a,b,c} since {a,b} is open and is contained in {a,b,c} by the definition of neighbourhood you provided above?
@Secret {a,b} is also a neighbourhood of a
I didn't say it contains every neighbourhood
@DHMO so by contain, we don't necessary need that be proper?
i.e. {a,b} contains {a,b} is valid?
yes
and I also use contain for $\in$
which adds to the informality
@DHMO Yeah. I thought you were looking for description of nbhds of the topology you mentioned, but apparently not
ok so that means: Any open set is a neighbourhood
15:25
@Secret yes, by definition
[That irrational set problem] I don't see how that induction can fail except it is weird that for each iteration (by picking a ratioanl z between x and y where x > y, and then iterate this process indefinitely to get to the result of dense) it means the open sets that can be unioned to form the irrataionals are becoming shorter in size yet have the same cardinality, and they are always countably many of them
so logically, those open intervals can get arbitrarily small. I suspect that might be how they screw up the induction proof
@Secret the open sets cannot be unioned to form the irrationals
because every open interval must contain a rational number
@Balarka I read how to show that $\pi_1(S^1)=\Bbb Z$ from Hatcher's, the whole covering spaces idea is fantastic, I would have never come up with it
o sorry I said that upside down. Let me check those facts again...
@AlessandroCodenotti Yeah, it's a fundamental idea.
The isomorphism is given by, as I assume you know already, sending a loop $[0, 1] \to S^1$ to the endpoint of it's lift $[0, 1] \to \Bbb R$.
15:33
[Recap]
Fact 1: Irrationals are not a countable union of open intervals
Proof: as mentioned above using countablity of rationals

Fact 2: By induction, the complement of union of closed intervals is a union of open intervals
-> Hint: This does not hold for irrationals. figure out why
@Secret wait, was that what I gave you?
Yep. I'll read it again in detail later because I want to have it very clear since I guess similar ideas can be used in more general cases
Feb 26 at 11:40, by DHMO
@Secret apparently fact 1 is true and fact 2 does not apply to the rationals
Sorry, I mean rationals
@Alessandro Indeed it can!
But I won't ruin the fun for you.
@Secret are you typing a long message?
15:37
Nope, I am thinking...
add oil
oil?
to his brain?
fish oil.
@s.harp it's a phrase only Hongkongers would understand :p
because omega 3 and stuff.
15:40
We have a phrase like that too
@BalarkaSen :o
@s.harp add oil is a transliteration of 加油, it means "Keep it up"
@Secret not a transliteration :p
you meant a word-for-word translation or verbatim translation
This is because 加 is add, and 油 is oil
Are there spaces with a finite, nontrivial fundamental group?
15:43
@Alessandro RP^2
The fundamental group is Z/2
It's also easy to convince yourself that the CW complex given by a circle, with a disk attached along the boundary by the map $z \mapsto z^n$, has fundamental group Z/n.
Indeed, for n = 2 this space is RP^2.
Hm, interesting, I'll think about it because I can't see it right now
Amusingly, the fact that RP^2 has fundamental group Z/2 has some implications in physics. (I specifically have in mind topological defects in liquid crystals.)
It's just that S^1 has fundamental group Z, and if you attach a disk along the degree n loop, then nZ gets modded out.
Also $SO(3)$ has fundamental group $\Bbb Z_2$
which has important consequences in physics :)
SO(3) is in fact RP^3
15:48
See this MO answer here for what I have in mind: mathoverflow.net/a/45838/55904
And has the same pi_1 as RP^2 because its the 2-skeleton
@BalarkaSen aha, that makes sense
@AlessandroCodenotti so the intuition of neighbourhood has nothing to do with nearness?
"nearness" is formalized via neighbourhoods
how?
15:54
I would rather say neighbourhoods are fat and coarse blobs around a point
@s.harp so are non-neighbourhoods
But non-neighbourhoods can be as fine as you want
the condition that something is a neighbourhood of a point gives it a necessary amount of fatness
@Secret ^
think about balls in metric spaces
a neighbourhood around a point is something that contains some ball around this point
this means it has to have some sort of inner fatness to it
that's because balls are the basis of the metric spaces
15:56
yes
but i'm talking about general point-set topology
if you make a neighborhood bigger in any way, it still remains a neighbourhood, making bigger can only make it fatter
well for general point set topology,I guess the fatness of nieghbourhoods is guarenteed by it properly contains an open set, so open sets are sort of something like a generalisation of a $\epsilon$ ball
@Alessandro Hm. What I wonder is if there is a subspace of R^3 with finite fundamental group.
@Secret I beg to differ. the balls are the basis, so their generalization is the basis
open sets are arbitrary unions or finite intersections of basis elements
15:59
Modulo nicety assumptions (eg, CW complex) it should be provable but I don't have one off the top of my head.
@DHMO yeah that makes sense, as open sets can also be a neighbourhood
@s.harp I'm afraid I can't help you with that
One rather irritating thing: As far as I know, there aren't any experimental realizations of topological defects classified by nonabelian homotopy groups.
That was meant as an answer to Balarka*
This phone is hard to use sometimes
Ok, I was confused
16:00
The ones I know of are all classified by stuff like Z or Z/n.
In principle the defects of a biaxial nematic liquid crystal should work like that, but it's never been observed.
Sure, @Alessandro, I was just throwing out a question
[That irratonal question] This is getting nowhere. The complement is not closed because it does not contains all its limit points e.g. 0
@Secret you need to attack the logic
namely, induction
16:04
It's an interesting question though
I'm so confused, i'm doing a simulation that runs some system along a gradient of an error function, independently of the random seed the error function first gets small and then goes up again to some stationary value
How can you pick closed intervals (the singletons) if the rationals are not even well ordered

Let P() be the proposition P(n+1) will be completely out of the window because there is no next one.

Now suppose we use that cantor zigzag mapping (forgot its actual name) to index the rationals so as to impose a well ordering(?), then the open intervals that result by taking the complement of say the singleton union [1/2,1/2] U [1/3,1/3] will be the reals with 2 holes. Now moving onto the next step of the induction, say [1/2,1/2] U [1/3,1/3] U [2,2] then you still get something with 2 holes beca
@Secret the rationals can be enumerated. We talked about this already.
@DHMO I know a recurrence for the rationals. I posted it on main and the question got deleted.
@Secret the complement of [1/2,1/2] U [1/3,1/3] U [2,2] has exactly three holes
16:16
No wait a sec... let me think again
Let me try to write out the induction and see what happens...
Let the rationals $q_i\in\Bbb {Q}$ be enumerated by the naturals $i\in\Bbb {N}$

Base case {$q_1$}, complement $(-\infty,q_1)\cup (q_1,\infty)$ true

2nd case {$q_1$} $\cup$ {$q_2$}, complement $(-\infty,q_1)\cup (q_1,q_2) \cup (q_2,\infty)$ true

Inductive case $\bigcup_{i=1}^k$ {$q_i$} $\cup $ {$q_{k+1}$}, complement $(-\infty,q_1)\cup (\bigcup_{i=1}^k(q_i,q_{i+1})) \cup (q_{k+1},\infty)$ true

Induction to the naturals
$(-\infty,q_1)\cup (\bigcup_{i\in \Bbb {N}}(q_i,q_i+1))$
-> ???
16:40
@Secret and then?
Ok, I don't really see any wrong logic here. The induction looks fine and thus the complement of union of closed intervals gives the union of open intervals
so you give up?
I recall you flashed one small hint before you deleted it earlier, something to do with the sequence (-1/n,1/n)
I am still trying to think how it fit in all of this
@Secret that was before I realized it was my question... and it isn't really relevant
"induction to the naturals" ?
16:42
@SteamyRoot I am sort of testing him, so I would appreciate if you leave this matter between me and him
Fair enough
Good luck :P
Then I am really stuck. Given how we can enumerate the rationals, thus avoiding the issue of well ordering and infinite descending sequences, and that so far by putting in singletons one by on I still not seeing anything weird popping out in terms of the logic, I don't really know what is happening and how it fail
@AaronHall which message is reported?
@Secret what do you expect me to do?
@DHMO Yeah, unless there's another hint, I gave up, I don't see anything that suggest something is not right
@Secret tell me what induction proves
16:46
Given a proposition P(m) for m < n, if P(m) is true, then m=n and P(n) is true
har.... what formulation is this
Because we are dealing with a countable set, we need to use transfinite induction
that isn't what you used
which generalise the usual induction up to n
@Secret this still doesn't make sense to me
16:49
If P holds for any number m < n, then P holds for n
that is better
but that still isn't what you used @Secret
Actually the $\omega$-th case should look like this:
$$\bigcup_{i\in \Bbb{N}} \{q_i\}$$
and then take its complement, but the problem is I don't know how to prove this since this obviously does not have the same expression as the base case and the successor case (what is said to be the inductive case above)
@Secret actually this is what I mean by fact 2
so essentially you already have the answer
but you said it does not hold for rationals, and I fail to see how it does not hold (other than the limit ordinal $\omega$ case may be false?)
The base and successor cases holds well
@Secret tell me what (the ordinary) induction proves
the one we learn in school
16:56
Show P(1) is true
Assume P(n) is true, show P(n+1) is true
Then P is true for all naturals
assuming that you learnt induction in school
@Secret so do you see how it fails?
Nope it still looks pretty fine
heh...

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