00:00 - 18:0018:00 - 00:00

12:59 AM
I would not disturb you. I'll get to you when I really need help. Now, I have to work with these things before I'd ask to you.

1:10 AM
@KannappanSampath ah, okay. I am now going to take Lilly for a walk. See you later.

1:38 AM
@Kannappan, just wanted to thank you again for your help the other day. The exam went very well.
Okay, these edits are getting ridiculous...

2:00 AM
@AntonioVargas Oh! Nice to hear that I could be of some help. Thank you for your compliments. :)
Can I see somewhere for the question paper for the exam? @Antonio

evening. am i in time for the math party

Hmm. This question always has a positive answer in this room. :D
Good evening BTW.

2:16 AM
@KannappanSampath I'll see if I can find the review sheet. I don't think the exam is available.

@AntonioVargas Oh, I see. That's a bit bad, I guess. But, never mind. If there was an hard problem which you cherished solving, I'd like to know too. :)

Actually the exam was quite easy. It could have been much more difficult. It was mostly regurgitation.
I'm thankful for that. I'm happy to be done with that class.

Oh, I see. Was it a group theory course or a General Algebra course?

The first half was group theory and the second half was fields and Galois.
(So, more group theory.)

8-) I know only about the groups. Not about fields or Galois.
Anyway, it was nice to hear you did the exam well. Congrats.

2:22 AM
Thanks :)

2:37 AM
Hi @Zhen

does anyone here use python on a windows computer?
program in python, that is

@EricGregor A little. What's up?

hey
@AntonioVargas i just have a question about which compiler to use
i want to start learning it tonight
i have a windows. i've heard some people use other versions of python, too, for math

Ok. It's not too hard to set up.

forget the names
i am downloading some compiler, just wondering if i should know about other options. i think a friend told me to get a certain compiler awhile back

2:48 AM
Are you thinking of Numpy and SciPy?

SciPy, i believe
Numpy sounds good though
number theory?

I haven't used either, but I was planning on getting to know them this summer.

are they just different packages?
or is the language modified?

They're just extra functions, I think.
extra classes
that type of thing

ok, so for learning there's no difference

2:52 AM
Yeah. There are probably some guides for how to use them to do different things, but mainly just think of it as python with some extra options.
I wrote this little guide for setting up Python, if you're interested:
http://mathstat.dal.ca/~antoniov/python_setup.txt

thanks!

so you recommend activepython
it's like a shell
i think i did this a couple of years ago and got confused

I like ActivePython just because it's so easy to set up.

maybe that would be good for me
one of the most tedious things in life is installing programs
even installing latex is a huge pain sometimes

3:00 AM
^agreed with that...

this gives windows a huge plus for me
i gave up on linux when to install basic programs i was scouring forums for information
because my installation wasn't going as expected

Yeah, totally.

I cannot integrate by parts...What am I?!!

@KannappanSampath Is this a riddle?

@AntonioVargas Rhetorical question posed to myself, quite loudly. :D
What would I get if I integrated $\int_a^bP^2(x)f(x)\mathrm{d}x$ by parts?
I know $\int_a^b f(x) \mathrm{d}x$

3:07 AM
is $P$ a polynomial?

Yes, I am trying out that problem from the main site. :)

I'm not seeing a nice way to use parts...

See, we have $$\int_a^b u v' \mathrm{d}x+\int_a^b v u' \mathrm{d}x=u(b)v(b)-u(a)v(a)$$
Now, I'd like to use $u=P^2$, $v'=f(x)$
But, what would $v(x)$ mean?

What about $v(x) = \int_{a}^{x} f(t) \,dt$?

3:23 AM
Why is that so?

Hi @leo.

@leo Hi!

@KannappanSampath Then $v'(x) = f(x)$, like you want.

@KannappanSampath are you busy?

@AntonioVargas HaH! Right!
@leo I am not at all busy.

3:27 AM
let denote $\mathbb{Z}_n=\{[0],\ldots,[n-1]\}$

then the order of $[k]\in \mathbb{Z}_n$ is $\frac{n}{(n,k)}$
right?

@leo Yes.

I'll return in a moment
ok

Sure you may...

3:30 AM
so, if $p$ is prime then the order of $[k]\in\mathbb{Z}_p$ is $p$?
@KannappanSampath right?

Yes, right. Because $(k,p)=1$ for $1 \le k \le p-1$.

indeed, then that's an answers to this

(So, $k \neq 0$ is a required condition there, but trivial one you know.)
@leo So, in the question there, is $g^i$ read as $g^i \bmod p$?
I don't comprehend the problem well at all.
I'll have to go and have breakfast. Be back in an hour or so. You may leave your reply with a ping for me @leo
BBL.

@KannappanSampath I just parse that as follows: $g\in \mathbb{Z}_p$, so $g=[k]$ for some $k\in\{0,\ldots, p-1\}$. If that is the case then indeed the above arguments answer the question
@KannappanSampath ok

@Eric, everything installing ok?

3:42 AM
@AntonioVargas i got distracted b/c a friend called. been moving slow. i just extracted eclipse straight to C://, now i'm trying to find out what to open there
i'm not stuck
i may be crashing really soon, i'm kind of burnt out. hopefully i can finish in a few minutes and make a quick hello world

Cool :) Just wondering.

@EricGregor learning Java?

python

I see. I have used Eclipse for Java, it is pretty good :-)

@AntonioVargas i don't understand what i'm doing here: pydev.org/manual_101_install.html
you linked to it and said i needed it, but i have no idea what it is and the instructions seem to presuppose knowledge of where to download something
maybe i already have this thing?
i'm awful with computers, i can only program when i have a clear language
i already opened the Eclipse program, so that doesn't seem to be what needs to be installed
i don't see a link to this plugin
ok, maybe i figured it out. i'm impatient, sorry

3:56 AM
Eclipse is like a big multi-purpose shell, so you need something to tell it how to use Python. PyDev is the plugin that does it.
@EricGregor No problem :)
The PyDev installation is the part of the setup process that takes the most time, but the instructions on that site are pretty good I think.

i don't get why this kind of stuff isn't more streamlined
is it really that much more work for this to be automated?

@EricGregor It is automated. Those directions tell you how to make the package manager set it up automatically.
Basically you're pointing the package manager at a URL and saying "Go!"

i don't get this line: "Then to actually import it, in the command line, go to the Eclipse 'java.home' directory and execute"
i don't see any java.home directory in the eclipse folder
it could be more automated. i could just click "python" or something

@AntonioVargas i'm not at that stage

4:02 AM
If the Eclipse team wrote the python plugin I'd agree.

i'm in the PyDev Certificate
there should be some way for programs to interface better with adding plugins

You can skip that step
Seriously, just skip that step and follow the instructions and you'll understand.

the instructions don't say which steps to skip

It's really quite as simple as pointing Eclipse to where to get the file and clicking install.

4:03 AM
"installing with the update site"
btw the line "Now, if you don't want that dialog to appear, it's possible to import the certificate before starting the installation process" is pretty explicitly saying that step is optional

oh, i see i misread you earlier
yes, i'm sorry antonio. i am actually very sleep deprived at the moment
as soon as this is done lights out!

Haha no problem.

eclipse is freezing!

Weird.

my computer kind of sucks
well i should be able to do this eventually with your site, it is indeed very clear, my foolishness aside
i must crash though, i'll do this tomorrow. thanks antonio!

4:11 AM
You're very welcome. Cya!

6 hours later…
9:43 AM
Morning : )
Is the mean king @robjohn around? I'm in need of an analyst.

@MattN what's up?

Yay : ) Awesome.
@robjohn I wanted to answer this but I'm not sure what I wrote is right.
Are you still there? Or did I pick a bad time or do you not like this sort of question?
I'll be back later.

10:00 AM
@Matt: is it clear that you can choose such a $\delta$? you want to choose $\delta$ small enough that $\int |f^\prime_n | dx < \frac{\varepsilon}{N}$, but $N$ gets bigger as $\delta$ gets smaller.
sorry. I missed you.

10:13 AM
@robjohn True, I thought of that too.

@MattN It might be workable. I haven't thought more on it. However, at first sight, it makes one question.

@robjohn Meaning it's probably not that easy? : )

@MattN It is not immediately obvious that such a $\delta$ exists.

@robjohn Ok. Thank you!
I'll think about it again later, need to go do some other stuff.
See you later : )

10:43 AM
Hi , I'm looking for values of x,y,z such that x+y+z = 15 , how do I solve it
I don't want to solve manually, is there any faster method or formulae?

@x4d33746153706c306974 5,5,5

wolframalpha is not solving it either

or you mean you want to know all the positive integer values?

@Ilya yeah , that is one , but could be 6,6,3 etc
@Ilya yes:)

Loops?

10:46 AM
@Ilya didn't understand what you mean :(

For x = 1, x<15, x++
For y = 1, y<15-x, y++
z = 15-x-y;
End
End

@Ilya wait, 1<x,y,z<7
@Ilya cool , nice solution , Thanks

what do you mean with x,y,z,<7?
you're welcome. not a very math question, though - stackoverflow better fits such questions
saw that

@Ilya well values of x,y,z are constrained to be in between 1 to 6
but sum has to be 15

you can use my code and print only answers which satisfy the constraint

11:00 AM
answer is 8 combination of x,y,z produces 15 as sum when x,y,z are 1-6
but your solution produces so much combinations

ok, then we can use loops from 1 to 7 but still, z = 15-x-y
and you should eliminate cases when z>=7
wait
x = 1..7, y = 15-x- 7(max for z) ..7
so the code is
for(x=1,x<=7,x++) for(y = 8-x,y<=7, y++) z = 15-x-y;
@x4d33746153706c306974

@Ilya awesome , thanks a lot , but can you help me figuring out this solution , how did you solve it?

1 hour later…
12:30 PM
Do we have a better tag than for questions about number-theoretic properties that combine arithmetic with string manipulation on base-10 representations? They are a somewhat popular "recreational mathematics" topic, but do not really match the tag description which mentions "congruences, greatest common divisor identities, divisibility, etc."

12:43 PM
@HenningMakholm Here is a related discussion from chat.
But it seems more to be related to base-10 representation of reals, not of integers.
Which is what you wanted.
:-(
I remembered we have discussed something similar...
Perhaps ?

However, I do not think that is bad for such question; perhaps in combination with ....

12:58 PM
@MartinSleziak I'm not convinced myself there is a problem either. I'm not really sure about adding (recreational-mathematics) to such questions -- it feels a bit like unilaterally adding (homework) without really strong evidence that the tag applies.

Well, homework tag is really special one.
But maybe a little....

Context: I was retagging this question.

I do the same thing - when in doubt, I leave tagging to OP and other users.

The concern is that retagging existing questions as (recreational-mathematics) could be understood by the OP as a criticism: "your musings have only recreational value" (which is probably often true but it's still a bit dickish to point it out explicitly without good reason).

That question does not seem like (recreational-mathematics).

1:04 PM
No it's not explicitly recreational. I do have some trouble imagining what other motivation it could have, but that might well just be a failure of imagination on my part.

1:16 PM
This is not a fortunate choice of username...

1:30 PM

1:52 PM
I wonder who thinks this answer should be undeleted. It's an anti-Cantorian rant with no connection to the question at all.
2

2:03 PM

@Rob Deleted answers are only visible to the users with >10k reputation and moderators.

@MartinSleziak Thank you for the info :)

2:24 PM
$\bigcap\{\{a,b\},\{a\},\{c,d\},\{e\}\}$ how does intersection of sets works?

@Templar It's the set of every elements that is in all of {a,b} and {a} and {c,d} and {e}. That is, unless some of your letters are equal, the empty set.

@HenningMakholm if it was $\bigcap\{\{a,b\},\{a\},\{a,c,d\},\{a,e\}\}$ then answer would be {a}?

2:39 PM
@Templar Yes, assuming that neither b=c=e nor b=d=e.

2 hours later…
4:22 PM
if it didn't take me an hour to do a simple homework question I might actually be able to pass the tests I think
If I am proving integrals do I find the derivative of the function or the derivative of the integral?

@Jordan usually to prove that a formula for an indefinite integral is correct, you differentiate the the integral

so I differentiate the part with the elongated S not the part with the + c

no, you differentiate the part with the +C that is the indefinite integral of the function inside the $\int\dots\mathrm{d}x$

man
I do not know why all my answers are wrong then

For example, To verify that $$\int\color{red}{x}\,\mathrm{d}x=\frac12x^2+C$$ you differentiate $\frac12x^2+C$ and get $\color{red}{x}$

4:40 PM
I must be getting the derivatives wrong, which is pretty sad since I have been doing derivative for like 10 months now

@Mariano: How did the March 29 note to read Chat Rules get pinned again and the April 14 one become unpinned?

how can the derivative of x/2 be equal to both x^2 / 4 and 1/2?
fuck
I was integrating

@Jordan did you ever install the MathJax bookmark?

yes

okay, so you can read my example :-)

4:44 PM
yes
I have been doing homework all morning and I havent done a single problem yet lol
still have no idea how to do math.stackexchange.com/questions/134844/…

@Henning: Good day! It is late afternoon there, I guess.
@Jordan you mean differentiate $\displaystyle-\frac {(1+x^2)^\frac{1}{2}}{x}$

tes

quotient rule, chain rule, power rule (twice)

@robjohn And an excellent day to you. It's about 19 here.

I am stuck with $-(1+x^2)^-.5 - (1+x^2)^.5$

4:51 PM
@HenningMakholm Oh, so early evening.
@HenningMakholm are you on daylight savings time now?

Yes -- CEST = UTC+0200.

Ah, I was using UTC+1 for you, but that was before the switch.

people say that if you get stuck on a problem you should move on, but I just end up completing no problems that way

@robjohn, no idea!

I finally figured out how to include diagrams in answers :-)

5:02 PM
Dat circle! :)
(that kind of diagrams can be drawn with acceptable ease using inkscape, with pretty good results)
(tikz, once you get the hang of it, is better for mathematically oriented illustrations which do not require "free hand" parts)

$$\frac{\mathrm{d}}{\mathrm{d}x}\frac{\color{red}{(1+x^2)^{\frac12}}}{\color{green}{x}}=\frac{\color{red}{\frac12(1+x^2)^{-\frac12}2x}\cdot\color{green}{x}-\color{red}{(1+x^2)^{\frac12}}\cdot\color{green}{1}}{\color{green}{x^2}}$$

Hmm, I have Inkscape installed, but I'd have to learn to use it.

@HenningMakholm is that a drawing program?

did you see the vixra papers thatsomeone posted on MO (claiming to prove Goldbach and what not) with very interesting "illustrations"?

@robjohn I think so -- vector based IIRC. I'm quite happy with Gimp for pixel graphics, but freehand drawing with a mouse is not among my strengths.

5:06 PM
you can even make inkspace export tikz graphics :)

@HenningMakholm Yeah, I use Intaglio, but that is just for Macs, so far.

@robjohn So far? They're using it as a sales point: "Because Intaglio is designed to work exclusively with Mac OS X, it’s able to take full advantage of ..."

@HenningMakholm Yeah, but I wonder if they might port it. Perhaps porting the Mac drawing capabilities they depend on might be too hard.

the "mac drawing capabilities" are simply PDF

Interesting definition of "entirely": This illustration was created entirely with Intaglio. CoreImage was used for lighting and text effects.

5:12 PM
at least the 2d part of Quartz is pretty much equivalent to pdf
@HenningMakholm :)

(Oh, it says "core image", not "Corel Image"...)

@MarianoSuárezAlvarez I think they use more than that. There are some geometric drawing routines built into MacOS, but I don't think they are too hard to port. There is a project at Google that ports QuickDraw GX to many platforms. Much of code that I have written is on the Android
@MarianoSuárezAlvarez PDF is a document preparation format. Do you mean PostScript?

there is a little difference between the graphics models in ps and pdf; quartz is more or less (or was, initially?) more or less an implementation of the same graphic model as pdf

@robjohn The PDF imaging model is a close relative of PostScript. Wikipedia claims that OSX is using PDF.

gnustep had something called Screen Postscript which was in the same spirit
maybe Display Postscript?

5:15 PM
The fact that much of the code that I have written is on the Android is why Steve Jobs hated Android (not that he cared about my code, but the fact that much of QuickDraw GX was ported).

ahh
right
operating systems converge to gnustep
just like programming languages to lisp

@HenningMakholm Ah, yes. Display PostScript. That can be encapsulated in a PDF.

@robjohn, things that are "hard to port" are simply those that depend on hardware
no one has any excuse today to say that code is hard to port...

Well, the actual drawing parts of PDF (encapsulated in more layers of different wrappings than one would think necessary) is essentially a subset of PostScript, with the drawing operators given short one- or two-letter aliases.

5:18 PM
(apple does have things that depend on hardware they only ship, like voice enhancing thingies implemented onchip)
but IIRC PDF does not allow for full postcript code

@MarianoSuárezAlvarez yes the ASC (Apple Sound Chip) has been a part of their motherboards for a long time. I wasn't sure it was still there.

a PS file can implemente a chess engine, have the printer play against itself and print the resulting list of moves...
PS is crazy that way :)

@MarianoSuárezAlvarez Yes, PS is a decently complete programming language.

in my youth I used to code in Forth

@MarianoSuárezAlvarez Correct. All of the conditional and looping constructs are absent; the PDF creator is supposed to expand that itself. That was a quite nice philosophy, since the Turing-complete parts of Postscript are essentially just DoS-enabling bling. But then PDF somehow acquired support for embedded JavaScript instead.

5:20 PM
which is an antecedent to PS
or a sibling
yeah
Mr Acrobat trying to become a virus vector :)
PDF files that connected to the internet
what were they thinking!

Trying to become a web browser is more like it.

The forms thing is cute, though

Just the top of a very slippery slope.

Because once you have forms, you also gotta have validation. And then the Turing gates are open.

5:23 PM
To Become The Word Of The 21st Centrury

I think they've shown remarkable restraint in not embedding a Flash player in their PDF reader.

@HenningMakholm Then Apple would have to keep PDFs off their mobile devices.

or not implement flash-in-pdf

Leaving them with a pretty boring device :-p

5:28 PM
it is not like they kept the web off their mobile devices!

@HenningMakholm well, those PDFs should not play on an iPhone or iPad. I wonder if they scan for Flash content in a PDF

Oh, my. I've capped.

@HenningMakholm :-p I've answered a couple of questions lately that have gotten absolutely no attention.
and 2/3 of my votes today have come from an old proof without words that some people must have rediscovered.

@robjohn But they're full of scary formulas!

5:35 PM
@HenningMakholm yeah, but they are elementary analysis.
I am mainly waiting to see if I can get 23456 :-)
I need 95 rep for that.
@HenningMakholm I hope that my votes weren't capped out.

@robjohn So far I'm just touching the cap.

I just checked that. I will refrain from voting on your posts now.

Let $f,g$ non-negative functions. Let $0\leq\eta\leq f+g$. Let $\eta_1=\min(\eta,f)$ and $\eta_2=\eta-\eta_1$. The clearly $\eta_1\leq f$ but I can't see why $\eta_2\leq g$. Can someone help me please?
$\eta$ is bounded and supported in a set of finite measure

@robjohn: It confuses me here that you're speaking of measures when the OP specified Riemann integrals from the beginning.

@leo $\eta_{\,2}=\eta-\eta_{\,1}=\max(0,\eta-f)\text{ and }\eta-f\le g$ and if $\eta-f<0$ we know that $g>0$
$g\ge0$ too late to edit the previous
@leo does that make sense?

5:53 PM
@robjohn yes. thanks! :-)

00:00 - 18:0018:00 - 00:00