00:00 - 17:0017:00 - 00:00

12:39 AM
its astounding that there are no comments on the video.

they are waiting for your comment

isn't stanford part of berkeley, so i guess including sri is ok...

I like when their master tellls them they can stop cycling

@Yorch i am sure they got dragged into it against their will.
in my life experience the power flow is in the opposite direction

what do you mean ?

12:43 AM
are you married?
that was rhetorical

no
but there's two people in the bikes
and the person filming tells them they can stop

i did figure that part out, thanks :-)

Cool

it's not the density of points in the plane, it's the density of plane in the points

I still don't know what you're saying
Is the working theory that the camerawoman is the wife of the dude on the bike or something?

1:00 AM
it was a broad observation on life, you introduced the term master, i was suggesting that it may not necessarily apply.
the point is the plane density

1:11 AM
Oh I see

i understood the SRI to be the silly valley one and not the berkeley one but could have been wrong.
stanford is berkeley's ugly stepchild.

1:36 AM
@TedShifrin SRI is listed in Berkeley, so I thought it was a precursor, but maybe not

Guys
Hello
Someone could help me?
I am having trouble to understand how to find the boundary condition for the continuity equation divJ + d\rho/dt = 0
Should J be continuous at the boundary?

@leslietownes You're right; SRI is the Stanford Research Institute.

boo. stanford sucks.
it's amazing now but in the 1950s-60s it was summer camp for rich people. although noted president herbert hoover did go there and did his best with a bad situation.
for a while at berkeley i worked at something called the electronics research laboratory, which is a little weird because i don't think i did anything relating to electronics.

However, the first ARPAnet communication went from UCLA to SRI
it was a logon

that's cool.
early internet stuff is very cool and if it didn't go to the basement of evans hall it is still OK with me.
even if it was, ugh, UCLA.
i do law recruiting there and the students are very sharp. and the math department speaks for itself.

1:58 AM
erl. that paid my way there.
i think my fave on campus place was the math library.
i miss humphrey gobart

@LSS More context might be needed.

2:16 AM
you are also an ERL alum? what a small world.

yep. i really liked hardware but saw none of it while there. the irony of it all.
i mean hands on stuff

i was designing an algorithm and we ended up giving up. electronics were not expressly involved.
i think they were in cory although the grant administrator for my project was in soda.

2:36 AM
meinkraft

3:05 AM
most of my time was in cory, then evans and i avoided rechtel if i could
i spend a good bit of time in the physics basements

3:23 AM
all of those places have been constantly slated for demolition for seismic reasons for 20 years and yet they have no money to replace them with anything.
they may have done campbell. that's where math was before evans.

4:03 AM
hello

good evening.

4:49 AM
hi

yo

the suspense is killing me.

drum roll...

expecting half a pretty female assistant to appear
i guess the best was hyperbole. back to simplifying my incomprehensible home it setup.

4:53 AM
always helpful to simplify the cabling.
i went off on a coworker once, not as you jokingly did but because as he unacceptably was treating a female coworker as a pretty female assistant. i was shouting. it is legendary around the office.
i just lit up. it's nice that my coworkers think it was ultimately funny. genuine behavior in that area, which is what that was, is pretty gross.
at home i joke more or less all the time about being a sexist pig.
my wife understands that the horrible things i say are a product of my environment and not who i really am.

@leslietownes and now she thinks she isn't pretty ;-)

oof, probably. i hadn't thought of that.

Hey, @Ted!

at home i say the worst things i can think of because i think they're funny, but if i hear them at work, it's game over.

Oops ... Didn't realize I was still logged in here. Hi, @robjohn et al.

5:00 AM
you just floated in

good evening mr. shifrin. we have your usual place at the window.
2

I was at duplicate bridge, but just came home and woke up the computer, yes.

Hullo @Ted :)

Heya Edward. Stranger.

Exams are over, I'm back to haunt
lol

5:02 AM
duplicate bridge; is that in case the original bridge fails?
You might need a contract to replace it

i've never played bridge. my grandmother was very into whist and the approximately 90 minutes of my life i spent with her were learning that game.

Bridge is a challenging game ... helps my brain not be totally dead :P
My grandparents played canasta, no bridge.

it seems to be very difficult.
oh, my grandmother loved canasta.

My parents had numerous bridge parties at their house when I was a kid. Pretty well guaranteed that I never played it.

my dad taught me a cool card game. it goes by the name of 52-pickup.

5:06 AM
I played pickup stix.

it was so funny.

My parents played casual bridge, but I only started learning in college, and then took it seriously only in my adult life.

there was a lot of it in 1015 evans when i was in grad school but i never understood it.

There was go in my day, not bridge.

there was some go, too. that is far too intricate of a game for me to be involved in.
it's really f---ing hard. pardon my french. in chess you can sometimes get over on someone with dumb tricks.
my one-year college roommate grew up in the soviet system and fancied himself a master at chess. he could only draw against me.
way too aggressive.
i never beat him but we drew all the time.
he'd always get into something. especially when playing white. he couldn't help himself.
chess is a psychological game.

5:14 AM
Hi Leslie, did you every play chess with an online bot named Boris? :)

i don't think i have. i have done some blitz chess with mixed results but i prefer the full game.
my playing style is slow and boring and just setting up the position with the most boring things imaginable.
it sometimes works but i often lose.

:) i used to play chess a lot, i was very inspired by style of Mikael Tal.

he was a complete inspiration.
i like viktor korchnoi.

the way he played was fantastic :)

korchnoi was great more or less forever, until he died. that is an inspiration to me.
and he would kill people by playing passively and then sliding in the knife.

5:19 AM
i never heard about korchnoi :-(

you should look him up. he almost beat karpov but did not. he would kill people at seniors tournaments.

yeah i'll look

he was alarmingly consistent in the quality of his playing until he died at age 85. we should all be so lucky.

i like magnus

he's amazing.
i don't even have words for it

5:23 AM
he sortof is an all rounder
he has stage presence, seems like a decent human

i have seen some of his videos where some challengers were found using engine and still they lost :)

yeah, haha. good luck.
i'd put my money on magnus.

for me chess is like table tennis & math, there is a level i play at and that more or less is it. depressing at some level until you accept it

copper that's exactly it for me.
i'm happy if i can beat people in my family, but i suck.

i improve by lateral moves :-)
in life

5:26 AM
it would be fun to see magnus vs stockfish 7 (is 7 the highest level of stockfish?)

and i can't win, i can only draw.
i've drawn against an IM.
enough for me.

i can grab defeat from the jaws of victory, i am creative but no memory for closings

a lot of the closing game does come down to memorization.

and openings, but i am usually more awake then :-)
somehow the olympics just not grabbing my interest

when i play i try to get out of the usual openings as quickly as possible just to see what the other person can do.
the olympics are boring me.

5:29 AM
to combat my memory i like 3+0 blitz

that's brutal but of course you would like it.

i'm amazed the world standardized on time but nothing else
i can drink wine and blitz :-)
no deep category theory thinking going on

we put out a cricket trap in our garage because there were too many crickets in there and then a lizard got into the trap and was immobilized by the adhesive and died. i feel really bad about that.

i don't like when things die at my hands, but what can you do

i did want the crickets to die.
i didn't know we had lizards in the garage, at all. i've seen them outside but not there.

5:32 AM
a little bird fell out of its nest prematurely
i leave it there.
my friend didn't want it to suffer so he crushed it with his shoe

80% of birds die more or less immediately.
i love birds but it's a fact

i know, but i'm still disturbed by what my friend did
we have done much worse, but this one was on the boundary of what i can handle

it is wrong to crush anything.

that would be my general option with one exception
earwigs

if something might be in pain, you kill it immediately. but you wouldn't crush an animal.
that seems wrong.
i don't know.

5:34 AM
he was quick about it, he did not want to inflict pain

in his defense there is very little chance of getting back to the nest if you fell out too soon.
he might have just put it back in the nest, though. it's an urban myth that birds will not care for a bird that has been handled by humans.

this was the case here. somehow years of catholic upbringing lets me believe some winged thing will rescue it :-)
the nest was out of reach
i would have taken that risk

well, sh-t.
the animal was not infected with original sin and is likely in bird heaven now.

i'm going to ask tarantino to make a movie about it, pulp friction
that was bad, even for me

but very much in character.

5:37 AM
the female volley ball teams are playing, a bit distracting
not really a volley ball fan

oh god, i went over this with my bff.
i don't understand the sport but do like people in skimpy outfits. she does too. i think that's the only reason it's an olympic sport.
just a bunch of people perving out about it

norway disagrees
the team refused to play in bikini bottoms.
capital offence i say.
at risk of misinterpretation, generally i think the human form in great athletic shape is something to behold.

i'm generally against the olympics because while there are a tiny number of rags-to-riches type inspirational stories it is mostly celebrating people who had an enormous number of resources growing up.
it seems like a misallocation of attention.
i'm still watching girls volleyball.

i knew a few hopefuls and have met some irish olympians (runners & boxers)
i have met a few us olympians
one was out neightbour at some stage
he had the distinction of being both a summer & winter olympian

that's weird.

5:42 AM
another taught my kids to swim
i never had any concern around water as a result
he was a totally nice humble guy

the only olympian i knew was born rich and had her parents put literally all of their time into her sports career. it seemed excessive, but that is the vibe i get from a lot of them, at least from the USA. too many resources poured into a very weird box.

i only found out when we went out for lunch (which we often did) and he was wearning a leather jacket with the olympic circles on it
"where did you steal that dave?" asked joe

that's 100% what i'd say.

"i was a summer & winter olympian joe"

we might be the same person.

5:44 AM
" nfw dave"
i mean he could at least have had some unlikable characteristic so i could feel good

one time i was at a legal event, and i was talking to someone whom i did not know was a federal judge who said he biked there, and i said "oh, DUI?"

:-)

he has since been on one of my cases.

@leslietownes The UK gold medallist for synchronized diving of some description was in my year at secondary school

i have met a few people in that manner with my lose cannon mouth

5:46 AM
not such a great guy. I commend him for his achievements though

diving is a dumb sport. i said it.

it's only dumb if there's no water under the diving board

my sister's running club is run by an irish boxing medallist

i can splash in the water. give me a few weekends and i'll be in the olympics.

i haven't swum in 1.5 yrs
swum swam?

5:47 AM
you just point at the water and go.
it's stupid.

The diver made some claims about having been bullied constantly, despite being wildly popular, and was moved from our state school to a massively over-priced private school on a scholarship

i love playing in the water, preferrably with waves and not freezing

no disrespect to your friend, edward.

He's a bellend
rofl

or acquaintance.

5:48 AM
a glans of a man?

bellend is one of my favorite terms in the english language.

A glans indeed

it is a problem when one comes up with a great sentence but you know your presnt company will just not get it
in fact they will think it is more than strange

my wife did sports a little bit in college and every one she was around was a toxic and horrible person. just really horrible people.

ll
lo*

5:49 AM
i spend my life trying to be more than strange.

wtf

odd. generally i found the athletic/sports folks to be decent off the field/mat
even the two olympic judo hopefuls who lived off the dole to support their sport

the athletic men i have known have been ok but apparently if you're a girl and you work with girls it can get very awful very quickly.

would not want to meet them in a dark alley...

Maybe it's being in a solo sport or smth

5:51 AM
my wife has a black belt in karate and was disqualified from a tournament for breaking someone's nose. which is why i love her.

lmao

i'm afraid i may have damaged a few noses & teeth

she just went right into it with the elbow.

not in competition though

which is how to do it, if anyone wants instructions.
i've mashed a few teeth out

5:52 AM
anyone watch mcgregor crap out recently?

elbow is the best way to do it, almost anything is going to hit hard

cringeworthy

your elbow is supposed to be super hard (prob urban legend stuff)

I've never really followed any sports except cycling, didn't even watch the tour this year though

5:53 AM
i was sort of a fan until he started rattling on about families
i like an eclectic mix.
i like watching friends & relatives play

the elbow just goes right in there. the best way is to fake a punch and then spin around and do the elbow. you hear it when it works.

nice!

A bat hurts too apparently

i probably do not align with conor politically, there seems to be some weird stuff there.

someone came at me with a stick once (in west berkeley) but i blocked it and the stick snapped
the chap was a bit shocked when i started towards him and he ran away

5:55 AM
the people who do that kind of stuff never have a second plan. that was what awakened me to the world of self defense.

i could have tackled him but i had the dinner
besides, it would not have ended well

they have the one thing they think is going to work and when it doesn't work, you've got 5 seconds and look out dude because it's my time.

Sorry for disturbing the nice discussion. I have a doubt: suppose that $\alpha$ is irrational then I know that there exist positive integer $q_n$ and an integer $p_n$ such that $|\alpha-\frac{p_n}{q_n}|\lt \frac 1{q_n^2}$. From here what can I say about $\lim q_n$ as $n\to \infty$?

what?? maths?

koro thank you for interupting the discussion of how to hit people.

5:56 AM
you mean other than going to infinity?

will $q_n\to \infty$?

you can find such $q_n$

I think that will be true if $\frac{p_n}{q_n}\to \alpha$.

i assume you've done the wikipedia stuff

it's an exercise problem in a book

5:58 AM
oh

it must be true if the rational quotient converges !!!!!

I was seconds away from sending a theorem

the first part was to show existence of ${p_n}$, ${q_n}$ such that $|\alpha-\frac{p_n}{q_n}|\lt \frac 1{n q_n}$

i find it a very peculiar result for reasons i cannot elaborate
$n q_n$???

You're proving the theorem I was going to send I guess

5:59 AM
@copper.hat yes copper, that was the first part of the question.

i see where its going

@copper.hat Hello. Can I ask you for a favor?

from here, that $q_n^2$ on RHS can be also be deduced

Can you tell me how many reopen votes have been cast for this post?

6:00 AM
but my question is what can we say about $\lim q_n$?

@Later i am not a mod
it looks like no reopen votes from where i am standing
and 1 delete vote

@copper.hat Thanks. Can I know the name of the voter?

similarly i am not a mod i just talk an enormous amount of b---s--- on chat and sometimes answer questions.

@Later i have no idea? how could i tell?

i just talk an ass load of crap.

6:02 AM
sometimes i like ass

@copper.hat You cannot see the delete voter?

@Later you mean the deleve voter? no, it just shows a count?

Yes

why would i see it and you not?

Because I am a low rep user.

6:04 AM
i have no special privileges other than being allowed ro answer convex psqs.
i don't think anyone except for a mod can see such things

my wife and best friend are understanding and realize i am an unhealed person but everyone else has some kind of reason about my posts and thinks, let's keep blocking it, and frankly i'm OK with that.

and i am far from a mod

Ok. Thanks.

copper and i are both in jail.
you're talking to convicts.

6:05 AM
i have tried blocking myself because if find myself disturbing
@Koro sorry, i missed the question?

lim $q_n$
The book says: since $\alpha$ is irrational, we have $\lim q_n\to \infty$
I didn't understand this statement

if the quotient converges to $\alpha$ then you Must have $q_n \to \infty$,

10 mins ago, by Koro
Sorry for disturbing the nice discussion. I have a doubt: suppose that $\alpha$ is irrational then I know that there exist positive integer $q_n$ and an integer $p_n$ such that $|\alpha-\frac{p_n}{q_n}|\lt \frac 1{q_n^2}$. From here what can I say about $\lim q_n$ as $n\to \infty$?

well, if $q_n$ is bounded above then you can only get so close to $\alpha$.

@copper.hat I know that. But from the inequality, is it obvious that the quotient ($\frac{p_n}{q_n}$) converges to $\alpha$?

6:08 AM
it is obvious from the $n q_n$ one, since $q_n \ge 1$.

Ahh yes!

it is usually an earlier step in a proof

thanks a lot copper, I understood. I'll take ahead things from here.

excellent!
the there is the bare chested tonga lad who many were drooling over

4 hours later…
9:45 AM
13

This is currently a partial answer, refining the idea given by @reuns. The series $\Phi(s)=\sum_{n=1}^\infty\ e^{-n^s}$ converges iff $s>0$ is real. Using the Cahen–Mellin integral $$e^{-x}=\frac{1}{2\pi i}\int_{c-i\infty}^{c+i\infty}\Gamma(z)x^{-z}\,dz\qquad(x,c>0)$$ with $x=n^s$ and $c>1/s$, w...

The remaining question is whether we can extend this region further.
^I don't understand this. Where else is it possible to extend to?

1 hour later…
10:47 AM
i just cant stop rolling my r's

11:01 AM
Hi, could anyone advise whether there is a standardised way to denote two versions of same variable. I am currently using $A_0$ for the initial revision and $A_1$ for the next revision but I wasn't sure if this is right? Many thanks!

Hi, I wanted to solve the integral: $$\int_{0}^{\infty} \dfrac{cos(tx)}{x^2+4}dx$$
using feynman's trick
If I denote this by $f(t)$, then $f"(t)$ will be:
$$\int_{0}^{\infty} \dfrac{-x^2cos(tx)}{x^2+4}dx$$
writing $x^2$ as $x^2+4-4$, we can further simplify this into
$$f''(t)=4f(t) - \int_{0}^{\infty} cos(tx) dx$$
But isnt this problematic? the integral obviosuly diverges...
Is there something I did which renders feynman's trick wrong or unusable?

11:54 AM
Oh i thought my doubt was be cleared but its not so, here it is once again

the limit is 0

oh yes e^(-infinity) from the graph, oh yes
Also want to confirm e^-(2/5) is not same as e^(5/2) right?

e^(-5/2) = 1/e^(5/2)

12:32 PM
@satan29 differentiating under the integral (Feynman's Trick) does not always work in all situations.
@cookies without any more context, I would say that that is correct.

@ComFreek thank you

@satan29 Try $\int_0^\infty\frac{\cos(tx)}{x^2+4}\,e^{-sx}\,\mathrm{d}x$ using Feynman's Trick, and then let $s\to0$. You can get $\int_0^\infty\cos(tx)\,e^{-sx}\,\mathrm{d}x$ by integrating by parts twice, I believe.

12:50 PM
"Fix $x \in I$. Then there is a number $M$ depending on $x$ such that $f(x) = P_n(x) + M(c-x)^{n+1}$, where $P_n(x)$ is the nth expansion of the Taylor polynomial at some number $c \in I$."
what's guaranteeing that $M(c-x)^{n+1}$ is a number here for all $x \in I$?

$\lim _{h\to 0}\left(h^{\frac{-2}{3}}\right)$
h--->0^(-2/3) how is it infinity??
or better question maybe, why is 0^(fraction that is<1) infinty?

@AdilMohammed notice the negative in the exponent makes you switch numerator and denominator

(Assume everything above as delete pls, i cant delete and it and I don't want people to think I forgot exponential formulas)

i always forget exponential formulas and im proud of it

1:02 PM
@AdilMohammed small numbers to negative powers get big

@robjohn - no worries thank you! :)

@shintuku when would it not be a number?

@robjohn (i am squeezing my brain currently, i remember my teacher telling you wont understand anything in this chapter unless you revise limit. Guess I'll have to take my last years book eeeee)

1:18 PM
@AdilMohammed For example, $\lim\limits_{n\to\infty}\left(\frac1n\right)^{-1}=\lim\limits_{n\to\infty}n=\infty$

1:44 PM
@robjohn oh, I realized that, since there is always a number that expresses the difference between a function and it's taylor polynomial, that expression is fine
thanks for the hint

1:55 PM
In differentiation of tan^4(x)
I used chain rule
Let t = x.
dy/dt = 4(tan^3) * t
dt/dx=1
So , answer is 4(tan^3) * x
But online , answer is different
Where am I going wrong

2:24 PM
@SrijanM.T $$y=\tan^4(t)\\\frac{\mathrm d y}{\mathrm d t}=4[\tan(t)]^3\times \frac{\mathrm d}{\mathrm d t}[\tan (t)]$$

@Wolgwang Ok thanks
@Wolgwang If integration of x^2 = x^3/3 +C. Then ,differentiation of x^3/3 +C is not coming x^2.
How come this is not true ?

Hey
Wanna watch a two-hour unedited Zoom conversation about knot theory?
2
In which I teach a mathematician friend about knots

@SrijanM.T It is $x^2$...

@Wolgwang
I get is 2x^2 / 3 by using division rule.
Can you tell where is the mistake or just in brief what to do @Wolgwang

2:46 PM
@SrijanM.T It is $(\frac{x}{3})^3+c$ not $\frac{x^3}{3}+c$

Ohkk @Wolgwang
Thanks a lot.

3:08 PM
mmh, $1^x$ can be 2
interesting
mmh, is it true: $1^x=2 \Leftrightarrow 1=2^{\frac{1}{x}}$, sure if x goes to infinity the right side is true, but feels wrong

I have done the same Calculus problem three times. I still get the wrong error. I think it is an algebra error. What is the best way for me to find the error? Any ideas?

3:26 PM
@robjohn but why
or more appropriately. what was in that particular integral that made it fail
@robjohn well the last integral is just the laplace transform of cos(tx) so its a known integral...

1 hour later…
4:41 PM
@satan29 you cannot apply the Leibniz integral rule blindly. the integrand in $f'$ is not integrable.
@SAJW for $x \neq 0$ we have $1^x = 1$, so the equivalence is meaningless.
@Bob you must be making a mistake. if you do not want to consider other approaches then you have little recourse other than to revisit your computations.

4:54 PM
@copper.hat how did you deduce that?

@copper.hat I don't know enough about complex numbers, so is it bogus or valid? youtube.com/watch?v=9wJ9YBwHXGI&ab_channel=blackpenredpen

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