Mathematics - 2013-03-14 (page 2 of 6)

κρανίοπεριπολία

10:05

@robjohn

>8(

Vrouvrou

hi

is there anyone ?

?

Ilya

10:23

yes

Vrouvrou

how are you

Ilya

busy :/

Matt N.

It's weird. Most of the time when I read Asaf's comments the image of an angry mob of chickens pops up in my mind. Same goes for Asaf's comments on meta, if not even more.

On an unrelated note: it's been chucking down snow here. Can't remember seeing so much snow in mid-March.

Michael Greinecker

10:40

@Ilya Hi!

Ilya

@MichaelGreinecker Hi, how are you?

@MattN. same here, we have a Christmas weather

Michael Greinecker

@Ilya Good, good. Bit cold though, it started snowing again.

Ilya

I wonder, if it's a present from Siberia

so sad - we had a really warm last week

Michael Greinecker

►

Ilya

@MichaelGreinecker I shall finally watch this movie

@MichaelGreinecker: anyway, I had a question to you, related to MDP

Michael Greinecker

10:45

@Ilya It is very odd, but great for people who like classic rock n roll

@Ilya What about MDP?

Ilya

@MichaelGreinecker suppose we have an MDP over Borel state and action spaces in discrete time.

Michael Greinecker

yup

Ilya

AFAIK, there are two ways to make this model complete: either assume continuity conditions (semi-continuous model)

or allow universally measurable stuff

Michael Greinecker

i think that is the usual approach

Ilya

I'm in favor of the 2nd one due to the generality and nice introduction in Bertsekas and Shreve

now, whenever we have a Borel measurable stationary policy, MDP becomes a Markov Chain

usual one, on a Borel space

can we say that the same holds if we fix a universally measurable stationary policy?

it won't be a classical MC, I guess...

Michael Greinecker

10:48

Hm. The policy is not the problem but the solution. Do you want to know whether stationary problems have stationary solutions?

Ilya

no-no

the point is that, I can assure some optimality of stationary policies, but those are not for sure Borel-measurable

user19161

Hey @ilya!

Michael Greinecker

okay

Ilya

suppose, there is an inequality I that holds over any MC

thus, it holds under any fixed stationary (Borel?) policy over an MDP

thus, it holds over the optimal policy as well

Michael Greinecker

Some almost-everywhere-inequality?

Ilya

10:52

everywhere. More precisely,
$$
|\mathsf E^\pi[U(h)] - \mathsf E^\pi[V(h)]|\leq\delta \tag{I}
$$

where $h$ is the complete history (=element of the sample space), and $U$ and $V$ are different utilities

say, I can solve the problem for $V$ and I would like to use it to approximate the solution for $U$

Michael Greinecker

Ic

Ilya

the point is that $(I)$ holds for Markov Chain, and thus for any Borel stationary policy $\pi$

even in case Borel stationary are $\epsilon$-optimal, I have $(I)$ for the optimal policies

but say I don't have the $\epsilon$-optimality

that's why I wonder, which kind of process is it, when I fix a stationary non-Borel policy

any ideas? @Michael

Michael Greinecker

So the question reduces to something like: Is the orbit of a MC induced by a universally measurable function almost surely equal to some Borel function induced MC? I guess not,otherwise we should get Borel optimal policies.

Ilya

@MichaelGreinecker hm, perhaps - I will bear it in my mind

Michael Greinecker

btw: this is a really cool introduction to relation between optimization universal measurability: jstor.org/…

Ilya

11:00

@MichaelGreinecker thanks, I'm still not very comfortable with analytic sets and the stuff

@Michael: btw! you may help me with my literature search, perhaps

Michael Greinecker

@Ilya I can feel you. That stuff is wild.

@Ilya I have to leave, I'm hosting a guest here today. I'll be around tomorrow. bye

Ilya

@MichaelGreinecker ok :) good luck - I'll try to catch you tomorrow in chat

Michael Greinecker

cu

caveman

11:36

@Ethan, that's Goldbachs theorem not Euler

facepalm math.stackexchange.com/questions/329911/…

the answer is totally wrong......

user19161

@caveman Hey, how is your revision?

caveman

and has been accepted

im not doing revision yet

how do you even accept such a wrong answer

user19161

@caveman Just comment on the post.

caveman

11:52

I posted an answer

even though he's answering a different quesiton, he doesn't even do that right..

user19161

@caveman You can downvote the answer if it is wrong to you.

caveman

it's not wrong "to me"

this isn't a subjective thing about feelings or whatever

Mats Granvik

12:25

I always judge the correctness of the answers to my stackexchange questions based on my feelings.

κρανίοπεριπολία

12:43

The questioner has that right.

Amzoti

12:56

Top-10 Reasons you might be an MSE addict!

10. You check your MSE stats a LOT. You occasionally get up in the middle of the night and sneak a peak.

9. Your significant other suspects you are having an affair with MSE. Even when you’re alone with your special person, you do find yourself thinking what other postings might be needing your insightful inputs right then…

8. You “mental solve” while driving or on the train, and sometimes even when you are alone in the shower.

7. You filter everything through your MSE approach and start giving it up- and down-votes, even watching a movie,with …

9

κρανίοπεριπολία

...you $\Huge\text{think}$ they are your friends even though you've never even met them!

user19161

@κρανίοπεριπολία Why not?

user19161

It's not as if people you do meet in person will stick with you through thick and thin.

user19161

But I am lucky enough to have some very close friends who will do that.

user19161

@Amzoti Hey Mr Regards!

Dominic Michaelis

13:07

@jasper you are gray is everything fine ?

user19161

@DominicMichaelis My colour is just what I like to see at that moment. You cannot interpret anything from it!

κρανίοπεριπολία

Haven't you heard, people can pretend to be your friend and it's harder to detect it on-line.

user19161

@DominicMichaelis Anyway, thanks for asking. I will email you again.

user19161

@κρανίοπεριπολία I just wanna point out that people pretend to be your friend in real life too. There's not much diff really.

κρανίοπεριπολία

... it's harder to detect it on-line

user19161

13:10

There are also different levels of friendship, and different levels of trust.

user19161

And yes, I have met enough assholes online and offline to know there are all kinds of people in this world.

Dominic Michaelis

what do you mean with "again" you never emailed me before ^^

user19161

@DominicMichaelis Yeah, that's right. I was wondering if that was correct, linguistically.

κρανίοπεριπολία

GN...

user19161

I am not sure now.

κρανίοπεριπολία

13:12

...GN

user19161

@DominicMichaelis I see you got two downvotes recently!

Dominic Michaelis

yeah but no idea for what

Jayesh Badwaik

@DominicMichaelis you can see them in your reputation change along with the post.

Dominic Michaelis

I see where i got the downvotes

but i don't see a reason for it

Jayesh Badwaik

ohh, that is an old problem.

Tobias Kildetoft

13:14

@DominicMichaelis people don't always give reasons

unfortunately

Jayesh Badwaik

it can be some people trying to get their reputation to a multiple of five.

user19161

Also, over time, friends can become enemies, and enemies can become friends.

JSchlather

@JasperLoy I'll probably just stick with JSchlather I've seen another Jacob here and there.

user19161

@MattN. Yes, I think the same as you. Asaf is quite comically angry it seems.

Dominic Michaelis

oh i still can get such a lot reputation today

i hope there come some nice questions for me

user19161

13:19

Although I am happy that I got many votes for the trig question, I am unhappy that I got less votes than the other answer.

user19161

That is because in my arrogant opinion, my solution is the simplest.

user19161

Anyway, I gave everyone upvotes on that post.

κρανίοπεριπολία

Good job.

user19161

It is also very weird that I got 3 votes today for a question I answered a few days ago, even though there is no bumping.

user19161

Sometimes, this happens because there is a duplicate or link.

Dominic Michaelis

13:26

bumping ?

user19161

Bumping means maybe a new answer or edit was made.

user19161

This pushes the post to the main page again.

user19161

It is then said to be bumped.

user19161

I don't upvote another person more than 5 times a day.

user19161

Otherwise, it will be removed by the script or the mods, or be suspect for sockpupetting.

Ethereal

13:29

I love this guy's name. It represents all of us

user19161

@Ethereal I don't use WA.

user19161

The only math software I use is the calculator, and also TeX.

Ethereal

@JasperLoy I like your dishonesty. :-P

user19161

@Ethereal I really don't use WA. I don't tell lies.

Ethereal

@JasperLoy It's fine... we lie sometimes :-)

user19161

13:31

@Ethereal In this case, I really don't use WA.

Ethereal

@JasperLoy Okay.

Dominic Michaelis

i don't use wolfram alpha i always use mathematica :D

Old John

Hi all

Dominic Michaelis

hi

anorton

Hi!

Just wondering... does anyone here know about generating functions? :)

Old John

13:42

not much

anorton

ok

I was just trying to solve a recurrence, and was running into trouble.

Tobias Kildetoft

@anorton what recursion?

anorton

@TobiasKildetoft math.stackexchange.com/questions/330292/…

oops.

2

Q: Generating Functions: Solving a Second-Order Recurrence

I'm self-studying generating functions (using GeneratingFunctionology as a text). I came across this programming problem, which I immediately recognized as a modification of the Fibonacci sequence. I wanted to place my newly found generating function techniques to work, so I tried to solve the ...

It's really a fibonacci sequence, but with larger rabbit litters... :)

$$a_{n+2} = a_{n+1} + ka_{n}$$

where $k$ is a positive integer.

Tobias Kildetoft

but where do generating functions come in?

anorton

To solve it...

Tobias Kildetoft

13:45

(I can see that one could solve it using them, but it does seem like an obvious way to go)

anorton

I know there exist formulas for solving without generating functions, but I wanted to do it with them, just for practice

Tobias Kildetoft

since $k$ is constant, this is essentially like a second order linear ODE

ahh, ok

been a while since I did anything with this

I know the book "analytic combinatorics" has a nice treatment of what happens to the generating functions when they satisfy certain recurrence relations

anorton

Hmm....

Tobias Kildetoft

but I don't recall the author, and I am not even sure if it has been published

anorton

I think I'll look into that book.

Would it be Sedgewick?

algo.inria.fr/flajolet/Publications/AnaCombi/anacombi.html

Sedgewick and Flajolet published a book by that title

Tobias Kildetoft

13:49

looks like the one

anorton

Ok. I have a copy of that... I'll look there.

Tobias Kildetoft

I read a pre-publication copy quite a few years ago as part of a course on this

well, read part of it I mean

anorton

Cool. That's pretty awesome.

anorton

14:02

Don't you just hate it when you make a simple (high school) algebra mistake??? :\ I made a mistake factoring in that recurrence...

Washu

Happy pi day :D

user19161

@Washu Why is it pi day?

user19161

OIC.

Washu

@JasperLoy en.wikipedia.org/wiki/Pi_Day

@JasperLoy going to make my pie when i get back home :)

κρανίοπεριπολία

4 hours ago, by κρανίοπεριπολία

$\Huge\text{Happy $\pi$ Day}$

Washu

14:18

@κρανίοπεριπολία :D

κρανίοπεριπολία

:D

24

A: How many digits of $\pi$ are currently known?

The current record is ten trillion and fifty digits. The last known digit is 1 .

Washu

@κρανίοπεριπολία wow that's a lot

that won't fit in my pie

κρανίοπεριπολία

Yep.

Dominic Michaelis

make a bigger pie

Tobias Kildetoft

it is only $\pi$-day if you write the date in that illogical american way

the real $\pi$-day is of course april 31st

Jayesh Badwaik

14:41

@κρανίοπεριπολία I am not sure that question is worth asking anymore, since now we don't have to calculate the digits serially and anyone can calculate any specific digit from $\pi$ using the formulaes with no requirement to calculate the previous digits.

@TobiasKildetoft I love you for saying that.

Tobias Kildetoft

next step is to convince people to add that day to april of course

3

Jayesh Badwaik

Another pi day is written in ISO format as far as digits allow, 3141/5/9

κρανίοπεριπολία

Jayesh Badwaik

@κρανίοπεριπολία That is a cool phone jacket/sleeve.

Dominic Michaelis

there is no 31 st april

κρανίοπεριπολία

14:49

7 mins ago, by Tobias Kildetoft

next step is to convince people to add that day to april of course

Dominic Michaelis

oh

i guess february don't mind to lose anthoer day

κρανίοπεριπολία

@JayeshBadwaik Yep, notice how you do math as soon as you wake-up?

Jayesh Badwaik

@κρανίοπεριπολία Haha. Yes. :-)

Washu

Math is everywhere

Dominic Michaelis

mh still got some pancake better

Washu

14:51

kicking my butt for not learning properly...

Dominic Michaelis

will make the rest

Washu

but one day i will :)

Jayesh Badwaik

@DominicMichaelis more like taking out a day from august to prevent double 31 in a row.

Will make counting easier for sure for many.

Dominic Michaelis

i can't count anyway

Jayesh Badwaik

Basically have 13 months of 28 days every year, and add five day extra week every fourth year. :-)

Dominic Michaelis

14:59

that would be better

Nimza

Good day!

κρανίοπεριπολία

hi

Nimza

What does mean a wedge product of differential form and current? $\omega \wedge [X]$ for example

@κρανίοπεριπολία hi

"meromorphic (1,0)-form $\omega$ is called weakly holomorphic if $\omega \wedge [X]$ is a closed $\bar{\partial}$-current"

aaaaa, got it

user19161

Ladies and gentlemen, I have capped for the day, thank you for your support.

κρανίοπεριπολία

yw

Dominic Michaelis

15:07

congratulations

i still need more than 100 ...

Tobias Kildetoft

I am still at 0 for today

anorton

@JasperLoy WHAT? How did you do that so fast?

I've never capped... :\

user19161

@anorton That is slow. Capping at GTM 0100 is fast.

anorton

Have you done that before, too? :D

user19161

Maybe a bit more than that, yes.

Dominic Michaelis

15:09

the fastet cap i made was at 8:00 GTM

user19161

Around GTM 0400.

user19161

Tomorrow I need to do something important, wish me luck.

user19161

Also, 640 more points to attain 20k...

Dominic Michaelis

i do

κρανίοπεριπολία

Good luck.

Dominic Michaelis

15:17

yeah good luck

user19161

I was thinking, if today is pi day, which day is e day?

anorton

@JasperLoy the 71st of February, what else? :D

user19161

@anorton I was thinking, maybe 27 Jan.

anorton

Ok... in that instance, I guess the American system of writing dates is a bit off...

Garbage Collector

@JasperLoy: Where are you?

user19161

15:25

@GarbageCollector I am in the world.

user19161

My actual location shall not be revealed.

Garbage Collector

@JasperLoy Oh, you changed your blue screen. I usually locate you by searching the blue box.

user19161

@GarbageCollector Yes, I like to see different colours.

user19161

@GarbageCollector The most reliable way is the user number.

Garbage Collector

@JasperLoy That is correct. Btw, I got 3 down votes for tex.stackexchange.com/questions/6676/…

Dominic Michaelis

15:29

without a reason as far as i can see

user19161

@GarbageCollector And what are the downvotes for?

Arkamis

Skullpatrol

Garbage Collector

@JasperLoy Maybe from the TikZ fanatics who don't like me to criticize the PGF manual.

user19161

@GarbageCollector I think each has its good points, let people use what they like.

Arkamis

@κρανίοπεριπολία You are a raiders fan, right?

κρανίοπεριπολία

15:31

@Arkamis Yep.

Arkamis

Then lament with me the treachery that has happened.

κρανίοπεριπολία

about?

Arkamis

For Wes Welker is now in your division, which means he is no longer on my team

user19161

What is Raiders? Is it baseball club?

κρανίοπεριπολία

NFL

Arkamis

15:33

Football (american football)

user19161

Ah, football, not soccer.

user19161

Of course, I call soccer football.

Arkamis

The Broncos just got about four times more scary.

Garbage Collector

@JasperLoy and @:8511208 you look nearly similar.

user19161

@GarbageCollector What is 6275?

Dominic Michaelis

15:34

i don't know if it is still snowing or snowing again

Garbage Collector

@JasperLoy The skeleton.

Arkamis

Seriously, and they signed Rodgers-Cromartie? What the fuck?

κρανίοπεριπολία

@Arkamis We ain't afraid of no DONKEYS HHHHHEEE HAAAWWW

Arkamis

You should be

Two years ago that team was starting Kyle Orton and people were putting up billboards begging for Tebow

Now they've got Peyton Manning throwing to Wes Welker, and just signed one of the best CBs in the league. This is like bizzaro world. If you told 2011 me that this was what the future looks like, I would have had you committed to an insane asylum.

κρανίοπεριπολία

There is a rumor that Chucky may return to the Raiders....

... or at least the NFL.

Arkamis

15:41

That's an annual rumor. I'm shocked it hasn't happened yet

κρανίοπεριπολία

I posted a question on the Sports.SE about the Raiders wanna see?

Arkamis

yeah

Is the entire text of the question just "WHYYYYYYYYYY??????????"

κρανίοπεριπολία

Funny guy.

Arkamis

I found it!

κρανίοπεριπολία

@Arkamis Good job Sherlock.

Arkamis

15:46

heh

Dominic Michaelis

@GarbageCollector i like the way the pgf manual is written f

Arkamis

The answer is basically "Al Davis."

He got old, and insisted on having his old crusty hands in the soup

κρανίοπεριπολία

He is the leader of the Dark Side

@Arkamis Big Al

Garbage Collector

@DominicMichaelis But unnecessary information makes it verbose.

Jayesh Badwaik

@GarbageCollector I did not find it too verbose. :-/

Garbage Collector

15:50

@JayeshBadwaik The talk about Karl's students is verbose (for me). :D

Dominic Michaelis

let me google verbose

i did find them funny

Garbage Collector

@DominicMichaelis Karl's students should not be explained too much. :D

Jayesh Badwaik

@Arkamis Do you have any idea about PSU and purdue computer science programs for undergraduate?

Arkamis

@JayeshBadwaik Not really.

I don't know much about CS in general.

Jayesh Badwaik

okay, no problems. :-)

Arkamis

15:55

Both schools have generally good reputations overall, though

My grandfather did his electrical engineering degree at Purdue, way back in the day.

Had a couple of friends who recently graduated there, but they were Civil Engineering and Nuclear Engineering, respectively.

κρανίοπεριπολία

You're a Pats fan right?

Arkamis

Yeah

κρανίοπεριπολία

The tuck-rule will burn in every Raider fans heart for the rest of our collective lives....

Arkamis

Legit call.

κρανίοπεριπολία

Too legit to quit.

Arkamis

16:02

Man, you might have gotten a bad break there

But that's nothing.

David Tyree -- and the five missed holding calls on that same play. The ball sailing through Rodney Harrison's hands. Welker's drop in 2012. Bill Buckner. Aaron Boone.

Really, being a Boston fan is a life of suffering.

2

user19161

@arkamis Why did you change your name?

Arkamis

@JasperLoy Because I wanted to distance a post from my real name somewhat.

Vrouvrou

hi

user19161

@Arkamis I see.

Arkamis

I made a fairly scathing analysis of the current way statistics are used in science.

user19161

16:06

@Arkamis So what?

Arkamis

Didn't want that to come up on a Google search. Many of the people who review my work have backgrounds in stats.

user19161

Oh, so work related.

user19161

Anyway, I think I won't go to the other room anymore. Too many people have hurt me there.

Arkamis

Which room?

user19161

Sometimes, I don't know if it is intentional. I can't guess people's thoughts.

user19161

16:13

Something could be said jokingly, or something could be said otherwise.

Garbage Collector

@JasperLoy I hurt you?

Jayesh Badwaik

@Arkamis What is the deal with declaring major after two years? Is it possible that one does not get to select a major because it is very competitive? (in reference to Penn State college of Engineering)

user19161

@GarbageCollector Not you.

user19161

Hey @peter how are your classes?

Peter Tamaroff

@JasperLoy Haven't started yet.

youtube.com/watch?feature=endscreen&v=L2cfxv8Pq-Q&NR=1

Dominic Michaelis

16:24

why is there no very low quality option for closing a question

user19161

@DominicMichaelis Aren't the other options enough?

Dominic Michaelis

it would fit for the homework questions where no effort is done

user19161

@Arkamis The Eng room.

Peter Tamaroff

@DominicMichaelis Because voting to close for "very low quality" would rule you out as a "bad person" to put it nicely.

κρανίοπεριπολία

@JasperLoy They are a bit strange there.

Jayesh Badwaik

16:27

@PeterTamaroff this has been posted here before.

Peter Tamaroff

@JayeshBadwaik What about youtube.com/watch?v=Uk-I85A5-hU

user19161

@κρανίοπεριπολία I never flag people in chat though, and I try to look at things in multiple ways before deciding what people mean.

κρανίοπεριπολία

@JasperLoy But that is JUST you ...

user19161

@κρανίοπεριπολία But it is true that everthing said has multiple interpretations.

Jayesh Badwaik

@PeterTamaroff Hahaha.

κρανίοπεριπολία

16:29

@JasperLoy Yes, context is everything.

Dominic Michaelis

my little pony

user19161

But there were two occasions in the past where I was really upset in that room. They were quite long ago.

κρανίοπεριπολία

Being upset in that room makes no difference to them I have found.

user19161

So I think I won't go there anymore, QED. Maybe they wanna get rid of me too.

user19161

After all, I am just a pineapple to them.

κρανίοπεριπολία

16:30

Perhaps.

You are a banana here.

Dominic Michaelis

bananas are no bad fruits

κρανίοπεριπολία

I enjoy them.

@JasperLoy It's better to be a big fish in a small pond, than a small fish in a big pond.

user19161

@κρανίοπεριπολία It's better to be a banana than a pineapple, QED.

κρανίοπεριπολία

Yep.

user19161

@κρανίοπεριπολία Yes, that is true.

κρανίοπεριπολία

16:39

@JasperLoy You are the $\huge\text{BIG BANANA}$ around here pal.

user19161

@κρανίοπεριπολία Anyway, I hope Charlie is fine.

κρανίοπεριπολία

Me too :(

@JasperLoy Like they say "if you can't stand the heat stay out of the kitchen."

user19161

@κρανίοπεριπολία Do you feel hurt by some people in there too?

κρανίοπεριπολία

@JasperLoy Yes, but I always try to protect my feelings on the internet.

Dominic Michaelis

i have no feelings, i am a man :D

do you know sledge hammer ?

κρανίοπεριπολία

16:49

Peter Gabriel?

Dominic Michaelis

i mean this one youtube.com/watch?v=SaiX24U0bNc

oh its in german wait a secodn

►

κρανίοπεριπολία

I $\Huge\text{think}$ I got him?

Dominic Michaelis

yeah

κρανίοπεριπολία

Not much of a thinker...

Arkamis

@JayeshBadwaik Some universities make people declare after two years because the first two years are generally all the same.

κρανίοπεριπολία

16:59

@Arkamis As a Raider Fan I am obligated to show you Patriot Fans this

Transcript for

$Mathematics$ Mathematics