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12:00 AM
edison's lightbulb filament, PCR, i don't know. a few synthetic fibers in the vein of gore-tex were also pretty sui generis but not the commercially successful ones. a lot of pharma is just people trying all 50 billion possibilities and finding which one makes a fluorescent thing light up.
which is fine as a form of invention but not the romantic view. i want the struggling artist in the garret.
 
¯_(ツ)_/¯
do you think this is cool?
this little kaomoji?
 
my best friend uses that all of the time. i don't know where she picked it up. we're in our 40s. i think it is the property of younger people.
i did not know the term 'kaomoji,' thank you. previously i just thought of it as 'one of those things that lauren does.'
 
I think the facial features are brought to you from the japanese hiragana alphabet
 
i had a vague sense that that had something to do with it. i like how it aligns everything with the horizontal. so many "smileys" from the old BBS days, and now, require you to turn your head. :-)
i used to use (: because i'm left handed. it drove people crazy.
 
12:26 AM
I think that's the russian way
 
That explains a lot about @Leslie.
 
i may have used it because it drove people crazy and me being left handed is just an excuse.
a little bit of me is the person who never sees a bull without wanting to wave something red in front of it. it's not out of malice, it's just an instinctual sense of humor thing.
i've read a number of profiles of comic actors who had this same pathology. they could never not be 'on' and it interfered with their ability to be real people. peter sellers and chevy chase are two examples.
i'm nowhere near as toxic as those people in other ways but i see the same thing in them that is in me.
 
if $f:\Bbb C\to\Bbb C$ is differentiable at $z_0\in\Bbb C$ then $\overline{f(\overline{z})}$ is also differentiable at $z_0$?
 
this is something i am guaranteed to mess up because of the number of order-2 things happening. the schwarz reflection principle comes to mind but this is not that. are you familiar with the cauchy riemann equations?
 
12:42 AM
I know C-R
 
the answer is no for very boring reasons
$f$ being differentiable at $z_0$ does not imply whatsoever that $f$ is differentiable at $\overline{z_0}$
 
yeah, wow, it may not even be defined there. this is why i was thinking schwarz reflection principle. if something is filling in potential gaps it would need to be known before the question can be answered.
 
oh damn sry, was moving my laptop
 
@leslietownes I let the domain of $f$ be $\Bbb C$
@Thorgott ok but I want explicit example
At least $\overline{f(\overline{z})}$ satisfies C-R
 
@Thor How was your lecture?
 
12:50 AM
you can write one down yourself if you internalize what I said
 
If the domain is symmetric, the answer is yes.
 
@Ted you mean my talk? hasn't happened yet, it will be next wednesday
 
Oh, oops
 
but my function is $\overline{f(\overline{z)}$ not $f(\overline{z})$
 
Yes, it's holo if $f$ is and the domain is symmetric. I already said so.
 
1:03 AM
hey Ted, lemme ping you again
@Ted, please take a look here
 
1:19 AM
@TedShifrin Is that due to schwartz reflection principle?
 
@TedShifrin you're thinking of something correct, but it isn't quite what sodam was asking. the answer to his question is negative.
 
He said domain $\Bbb C$.
 
for the sake of clarity:
False: if $f$ is differentiable at $z_0$, then $\overline{f(\overline{z})}$ is differentiable at $z_0$
Correct: if $f$ is differentiable at $z_0$, then $\overline{f(\overline{z})}$ is differentiable at $\overline{z_0}$
 
Oh, ok, Thor is right. I was making it holo on domain.
I should resign.
Schwarz reflection uses this.
 
i had the pieces i just couldn't or didn't put them together.
 
1:24 AM
@love_sodam it you meant analytic then it follows from the power series.
 
yeah, Schwarz reflection is very nice
the part about a continuous function that's holomorphic on both half-planes being entire pops up in the complex analysis proof of Fourier injectivity that I'm fond of
 
@Lucas I'm on my iPad so I do not want to type much. You can extend the module definition to arbitrarily many factors. What is your issue? In analysis/geometry, vector spaces (i.e., tangent spaces) are the relevant algebraic entities.
 
i like morera. simple and powerful.
 
Agreed.
Especially when coupled with Fubini.
 
ratner did a lot of stuff from morera's theorem. maybe she got royalties from the morera estate.
 
1:29 AM
fubini/tonelli is very powerful, it gets glossed over quickly i think.
 
Really? It's the main thing people remember.
And MCT and DCT, of course.
 
I still wonder why that is false and that is correct I can't find example
 
i prefer the supini theorem.
 
well, the interchange gets top billing, but the measurability of the partials can be very useful.
maybe is spend too much time in the gambling world...
 
I read the statement of schwarts reflection principle but the assumption doesn't match. It's much powerful
 
1:32 AM
What's a function that is holo at $i$ but not even defined at $-i$?
 
let me, let me, let me...
 
@TedShifrin It's not real on the real axis...
 
has the makings of a song...
 
sounds like a country song...
 
warbles
 
1:36 AM
interesting man Kary Mullis.............at least according to the wiki article........
 
strange is how i would put it.
entertaining party company
a bit mad.
every time i hear sade's smooth operator my mind floods with differentiable thoughts
 
@copper.hat I was in grad school working on pseudodifferential operators when that song came out
 
similar era
how apropos
@dc3rd mullis was an interesting character, had a very eclectic collection of beliefs.
 
1:54 AM
0
Q: Write the contra positive of the following statement.

Unknown xWrite the contra positive of the following statement. Suppose $x\in \mathbb R$, and we know: for all $\epsilon \in \mathbb R$, if $\epsilon>0,$ then $x\leq \epsilon$. Then $x \leq 0.$ The contrapositive of the statement is If $x>0$. Then there exists $\epsilon \in \mathbb R$ such that $x>\epsi...

Is my contrapositive statement is true?
 
2:07 AM
Hello, in modular exponentiation algorithm with factoring. Do you have any clue why $14^{105} \bmod 5 = (((14^3)^5)^7)$. Then we have $14^3\equiv 4\ mod\ 5$, then $4^5\equiv 4\ mod\ 5$?
 
Look up Fermat's little theorem.
 
the answer to the first question is probably that 3*5*7=105. the rest, let's ponder.
 
@Unknownx somebody verified that it was correct in the comments.
but yes it is correct
 
Thanks
@dc3rd It can be proved by taking $\epsilon=x/3$. right?
 
what can be proved?
be a little more precise.
 
2:13 AM
no....$\epsilon$ cannot be dependent on $x$
also as @copper.hat says be more precise.
 
@Avra Btw, modular exponentiation 'using factoring' is pretty much useless for all non-trivial computations. Because you can't factor. What you really need to do is to write the exponent as a sum of powers of two and use the 'square and multiply' algorithm.
In mathematics and computer programming, exponentiating by squaring is a general method for fast computation of large positive integer powers of a number, or more generally of an element of a semigroup, like a polynomial or a square matrix. Some variants are commonly referred to as square-and-multiply algorithms or binary exponentiation. These can be of quite general use, for example in modular arithmetic or powering of matrices. For semigroups for which additive notation is commonly used, like elliptic curves used in cryptography, this method is also referred to as double-and-add. == Basic... ==
 
I think I still have no idea how to prove if $(v_1,v_2,v_3\in\Bbb{R}^3 )xv_1+yv_2+zy_3=0$ has infinitely many solution then the vectors in that linear system is linear combination of other two and that two are not collinear 😅
 
@leslietownes. Thank you :). @feynhat. Thank you too. I was just wondering why 14^3≡4 mod 5, then 4^5≡4 mod 5?
Does they inject the mod inside brackets each time?
 
It doesn't span cube for sure
 
I mean: (14^3 mod 5) mod 5...etc
 
2:16 AM
@user863565 It could be that all three are parallel. So you cannot eliminate that case. But so what?
 
Sorry I meant ((14^3 mod 5)^5 mod 5) ...etc
 
@dc3rd I mean assuming x>0, we need to prove thre exists $\epsilon>0$ such that $x>\epsilon$. Here we can find $\epsilon=x/3$ such that $X>x/3$
 
@Unknownx that is fine.
 
Thanks
 
if you get your cases straightened up :-)
 
2:18 AM
@TedShifrin Yup .(it's really embarrassing that I couldn't prove this statement)😅
 
@Avra yes, the operations 'taking exponents' and 'going modulo 5' commute. For the second part you need little Fermat.
 
Well, write down $v_1+2v_2-v_3=0$ and think about it. (This is just an example. Your constants might be different.)
 
@TedShifrin I have already done that and may be I think I will try to think about it again
 
@feynhat. Thank you.
 
because there are so many overwhelming cases that v1 v2 and v3 will be different
 
2:21 AM
Of course. But rewrite that equation. One step.
You're thinking too much about concrete numbers, I think.
Think about the picture.
 
oh my bad now it makes sense lol
I already thought about this process but you are right I was thinking too much about concrete numbers
 
OK, lesson learned, I hope :)
 
$xv_1+yv_2=-zv_3$ I thought about it before and only now I notice yeah it's linear combination of two vectors
 
That works as long as $z\ne 0$.
 
I've just joined the club of "post deletion" when trying to provide help...............
 
2:27 AM
Do you expect a badge of courage?
 
tip of the hat maybe?
 
Well, my hat is in the other room, but OK.
 
"earning some stripes"........I could walk past the big boy table now.....:) can't sit down yet though
 
@dc3rd club of "post deletion"?
 
https://math.stackexchange.com/questions/4095033/write-the-contra-positive-of-the-following-statement

I was helping somebody after Ricardo had given them an answer, but I went to go look back at the question and it was deleted
 
2:34 AM
@Avra $14^{105}\equiv4^{105}\pmod5$, and if $(a,5)=1$, then $a^4\equiv1\pmod5$
 
anyways....not important
 
@dc3rd Oh yeah, that is not fun
@dc3rd I would have undeleted the question and reprimanded the OP, but the answer was deleted by the author, so there was no answer when the question was deleted.
However, there were a lot of comments given, so it might be appropriate to undelete.
 
Particularly bad since that very post was settled in here ...
 
3:05 AM
@TedShifrin i dislike questions deleted after getting help to hide the fact that help was gotten
 
@robjohn I want mods to sanction such behavior.
I've flagged a few times for that.
 
i wonder why the platform allows it as a default. maybe in other areas it makes more sense. that really upsets me.
 
Prosecute!
 
we file tomorrow. the process server is already on the way to that guy's house.
 
Good man.
 
3:09 AM
I believe that all the mods on this site will undelete and leave messages regarding this, but I don't think that anyone will be suspended for this. Perhaps if they repeat the behavior they might be.
 
I think there should be a standardized warning (like two strikes and you're out).
 
This sounds like something that needs discussion on meta
 
gosh, i always seem to miss the fun.
 
@copper.hat no, we just wait until you're gone
 
we can't all spend our days fussing about in tilden park.
 
3:12 AM
:-) i know that story!
it was down to emeryville on the waterfront to get my rna going.
 
@robjohn If you want my support or collaboration, let me know.
 
you think people delete so their instructors cannot find them?
 
@copper.hat that seems to be the case
The instructors probably would never see it, but that doesn't seem to matter
 
i am little miffed that the covid influx has changed the character so much.
 
this was going on long before that
 
3:15 AM
@robjohn there was no full fledge answer to the question. Ricardo answered him in the comments
 
@dc3rd There was an answer...
 
another parasite. my word of the day
 
actually, it was more of a hint, but it was given in an answer
 
Oh...I didn't even see that.
 
do you get a t-shirt when your rep hits 200k?
 
3:17 AM
@dc3rd You need 10K to see deleted posts
 
I'm quitting the site when I get to 100K.
 
@copper.hat I think I got swag for 100K.
 
yeah, i got that but i was hoping for a nicer t-shirt :-)
i do like the mug.
 
@TedShifrin I use the MSE mug all the time
 
my offspring try to hide it when friends are coming over
 
3:18 AM
@copper.hat exactly!
 
Most of my named mugs have worn out.
 
i have 3 mugs i am proud of.
mse
an ad slogan for cadence ("size matters")
 
:57595442 You can up-arrow in the edit field to edit old comments
 
my own company of decades ago
 
Wow ... I have nothing. I guess I'm too mean.
I did edit and it duplicated.
 
3:20 AM
hmmmmm
 
I edit constantly when on iPad.
 
i have a mug from dublin city university. i don't even know where i got it. it's my main mug.
 
why does the ad say "cut the cable cord"? just cut the cord or cut the cable.
dcu? how did you get that?
that is known as university college dublin (ucd) for dyslexics
they tried to recruit me a hundred years ago to do kalman filter stuff i think.
 
i'm working it back in my mind. my wife's mother went there a few years ago, maybe got it from her. i sometimes work with a guy who is a professor there but nobody who works with me gives me mugs.
 
wow, did not expect to see dcu here!
that's two surprises today leslie.
 
3:24 AM
i'm actually involved in a case where basically all of our information is coming from a DCU prof. or ex-prof. i think he's retired now.
 
almost worthy of a cab
 
sharp folks in dublin.
 
i really consider myself a corkman, but i was born there
there's dublin and everywhere else.
despite my origins i am not a city guy
can hold my own on a farm though
pcr & dcu in one day.
 
Udder delight.
 
what a teat :-)
 
3:26 AM
And then you went on the lamb.
 
my associative memory has hit its short limit :-)
 
but only half-cocked
 
More whine?
 
actually, the slang for skipping school where i grew up was "on the lang". no idea of the origins.
 
given the smallness of the world i expect that we have a mutual acquaintance. too much overlap.
 
3:28 AM
tempted but abstaining for my annual tomorrow
i am sure we have legal overlap
 
i might be suing you right now.
 
plus i know where you live
both living up to stereotypes
i don't have those sorts of connections any more.
although...
 
i know a lot of bay area semiconductor people. via work, mostly.
 
my sister visted many years ago and lost her camera in santa barbara
if was found by beverly hills police
 
That's far from Long Beach.
 
3:30 AM
who went through the pics
and found a license plate number
called dublin castle
 
geographically not far, in terms of traffic, very far. might as well be timbuktu.
 
who contacted the consulate in sf who rang me next day.
and we got the camera back.
a year later.
i think the police man was on vacation. i suspect he was not your regular variety
 
that's a surprisingly cool outcome.
 
i like the story. one more for the pile.
i was slapped at a party by the head consular officer in sf a long time ago
am i repeating myself?
quite feasible. finite graph of stories.
 
irish people just do that. potatoes flying out of windows, or breaking windows. slapping. it's how we have fun.
 
3:33 AM
a canadian consular aquaintance was complaining that whe you have 10 irish people at your dinner party you have 10 independent conversations going on simultaneously
it too about 2 decades to find out why i was slapped. entirely non obvious.
not worthy of repeating here.
 
at least you didn't get hit in the head with a potato.
 
:-). love those little guns
 
oh they're too much fun. i was almost arrested for using one of those once. i ran faster than my friends who were arrested. and did not tell.
 
:-). i was never arrested. i went to the station voluntarily.
for 'borrowing' a cabbage.
we left a fiver behind which a neighbour verified, so we were good
 
there was a guy in our town who was a huge racist, and had taught his kids to torment his neighbors, and we thought it would be fun to fire some potatoes into his living room. nothing violent, just potatoes. and it was quite fun to do that.
 
3:36 AM
think the internet is fast, try irish police.
we used to do that sort of stuff.
i got caught once and took a beating.
gosh, so many memories that i had forgotten about!
 
we just thought that maybe the presence of some tubers in his living room would improve his point of view.
 
potatoes work well with sling shots (we called them catapults).
and a lot of folks had corrugated roofs on their outdoor sheds
how totally irresponsible of us.
i would not have survived growing up in the usa.
 
oh i also got very close to quite a bit of trouble with a slingshot. it was the same guy actually, his son used to torment my sister so i tormented them back. ball bearings through the windows of his house.
nobody who knows me now would recognize the person who was doing this.
 
suffering from waves of guilt at the moment. and then you brought up the ball bearings.
 
hahaha
it surprises me that slingshots are legal.
 
3:43 AM
you had to be an adult to get one from the shopkeeper. but we knew the right adults.
yeah, the fuss with guns when you can get something like a slightsshot.
 
mine was 'borrowed' from a neighbor. we didn't have enclosed garages in our neighborhood, we had 'car ports.' and i knew where they kept it and i borrowed it, used it, returned it, with nobody the wiser.
 
we used to do that with boats (dingys)
but everyone knew about it.
 
borrowing without asking is just fine as long as nobody needs the thing while you've borrowed it. this is a moral instruction i intend to impress upon my daughter.
sometimes i tell my wife the stuff i got up to when i was a kid and she's horrified by it.
 
given the responses i get to the filtered stream i decided to write on mse instead.
you did whatttttt
different reality.
 
i'm like "sorry, did you not have racist jerks in your neighborhood? what would you do?"
 
3:46 AM
there was a sort of rough justice growing up.
one newish elementary school leaned a little heavy on a kid. the following monday he showed up all black & blue.
not suggesting it was right, but he was gentler subsequently.
 
it's also different being a girl vs. a guy. people were always testing me physically and i developed tools to deal with that. growing up as a girl is more of a psychological experience.
 
yeah, i could not deal with the psychological stuff.
 
it's much simpler if it's just "i want you to stop doing what you're doing, so i'm going to hit you." the mental stuff is another level
 
it was the same with our teachers. the physical ones were actually respected. the mental ones, well...
looks like a logic question to me :-)
 
the syntax leaves something to be desired, but you could spend days with kaplansky's formula. martin argerami provides really good answers in operator theory. i think i met him once but i don't remember.
there are a few people who comment on my answers, and i comment on their answers, and i'm pretty sure i know them from somewhere.
but it's all smoke and mirrors.
actually i did meet him at a conference. i remember now. he worked with several people i worked with. very sharp.
 
3:53 AM
@dc3rd question is undeleted if you want to post an answer.
 
there's someone else who sometimes snipes on operator theory questions before i can get to them, and i know him because he's another student of my advisor.
 
i have never met someone i knew before here.
which is a little surprising.
i did meet someone from here once. in caffe med on telegraph.
its my meeting someone from the internet story at parties.
love the shocked look first, once i met someone...
 
i hated that cafe. the cappuccinos were terrible. but i liked the vibes so i'd go there anyway.
 
i liked the vibe and the motely cast. the grump bar fellow (forgot his name) was not a reason to go there.
 
it seemed like more of a coffee place.
 
3:57 AM
i just liked hanging out there. and moes was across the road and codys at the end.
bar as in coffee bar
forgot the right term...
 
i went back right before the pandemic and literally everything i used to go to was gone. or closed. it was not a great time for me.
 
only moes is left.
cafe roma is cafe strada.
still old profs trying to hit on young pretties.
 
i met my wife in cafe milano. right by telegraph and bancroft.
very bad coffee drinks, i always got the tea. it was the one thing you could get for under a dollar. i expect it costs more than that now.
 
there used to be a baskin robbins there if i remember
and an orange julius on the corner of telegraph
 
for about half of my time in berkeley/oakland i lived behind a double rainbow on college avenue. it was great. and then it went away.
 
4:02 AM
where is how i learned the different between irish chips and american chips
hey, where are my chips?
 
haha i'm asking for the actual chips. which i ordered. hello?
america's supposed to be good about service, where are they.
 
to be fair, it was a language issue and i am in his country
plus he probably could not understand a word i was saying
 
4:22 AM
another $-{1 \over 12}$ question. so much real stuff and this is what garners attention.
 
I am extremely sorry for deleting the question. I won't repeat it again.
 
the unknown deleter...
you generated some excitement here
 
sorry
 
i don't know what happened, just that something happened
 
i won't repeat this behavior.
 
4:33 AM
Jimi hendrix is amazing.
 
5:12 AM
@BalarkaSen @SayanChattopadhyay I promised this centuries ago but do you guys still wanna hear a 'proof' of Kontsevich's recursion formula?
 
6:03 AM
hello everyone
any ideas on how to solve $$(D^2-1)y= xsinx + (1+x^2)e^x$$
 
6:38 AM
 
Hello guys I don't understand the notation of nth order ODE F(d^ny/dt^n,...,y,t)=0
 
Here, they show how to derive the value of 2 order determinant
Now , after solving for x and y . I got these values
What I noticed is that they put green colour value in 2nd equation and not 1st one. Why is that ?
 
What is meaning of a "V-shaped recover"?
recovery?*
 
Why don't you put them into the equations and find out why @SrijanM.T ?...You'll get the answer of why they do that.
 
@RajorshiKoyal please stop asking your non math questions here.
 
6:52 AM
Are we not even attempting to look things up online now @RajorshiKoyal ?
 
@satan29 solve for $x$? is $D$ a constant?
 
D is the differential operator...
the LHS is y''- y
 
So you're solving the differential equation then.
 
7:14 AM
yes..
 
 
1 hour later…
8:32 AM
When calculating the slope for the curve AB , who do we take tan theta and not tan alpha.
Ik AB is a curve but tan theta is bigger angle
Right should alpha
 
what is alpha ?
 
Angle between Delta x and the slope
This is what I think the answer should be. Am I right ?
a,b,c,D are values of f(e)
 
9:15 AM
@SrijanM.T That is what $\theta$ is, just taken at a point further out. The whole point of taking the limit is that the triangle gets smaller and smaller, getting even closer than where you drew $\alpha$.
 
Ohk. @robjohn I got it now.
My tan (theta 4) is right ?
 
sure (but for the straight line, all the tangents will be the same)
 
Yes. But it true that tan theta 1 is not equal to tan 2 , 3 or 4
 
@SrijanM.T in your diagram, with the straight line, they are the same. In a more general picture, where the line is replaced by a curve, they might not be the same.
 
Ohk.
Let us say if values of a,b,c = 1cm ,2cm,3cm and e = 4cm. Then , how is 1/4 = 2/4 = 3/4.
 
9:25 AM
@SrijanM.T No, if you take the tangent, you do not divide all of those by $4$ cm
you divide them by the particular $x$ value associated with them
the tangent is the $\Delta y$ value divided by the $\Delta x$ value
 
Oh ohk
Yeah. I saw that
 
The $\Delta y$'s get smaller, but so do the $\Delta x$'s
 
Yes
Just last Q sir
Here , if f(y) inc , then so will delta x and delta y
But , if we make f(y) small and x inc on condition , why is dy/dx negative
 
You should really try to use MathJax, it would keep everyone here from having to squint at the images, and even make it possible to use pieces of your formulas.
let me look
 
@robjohn Ohk. Sure.
This is the image of required to see
 
9:30 AM
If $y$ is decreasing with $x$, then $\Delta y\lt0$ when $\Delta x\gt0$
So $\frac{\Delta y}{\Delta x}\lt0$
@SrijanM.T In that figure, $y$ is increasing with $x$
 
Ok.
@robjohn So ,when we say y is decreasing with x.
So , there two names in the figure
delta y and y
How is it even possible if f(y) decrease
x will increase
Also , delta y = 0 should mean that a small number - big number
That is what I’m not getting. if f(y) . So does it decrease from point B
or point A
 
$x$ increases from $A$ to $B$ so $\Delta x\gt0$
in that picture if $x$ increases, $y$ increases. If $x$ decreases, $y$ decreases
$\frac{\Delta y}{\Delta x}\gt0$ either way, whether you go from $A$ to $B$ or $B$ to $A$
 
9:56 AM
@SrijanM.T: in that picture, the tangent is negative
As $x$ increases, $y$ decreases, and vice versa
 

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