Wolfram Mathematica - 2012-07-19

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12:25 AM

0

Q: Two UI small glitches. Please confirm

The red circled links don't work, and the blue circled box is superimposed. I am not tagging it as a "bug" yet since I suspect there may be some cache problem somewhere in my upstream internet proxy chain. Please confirm.

discussion support

@R.M So, they're augmented matrices? Weird. I'll have to look at it again.

Seriously?!? [B|AB|---|A^(2n-1)B] is a list of matrices {B, AB, ..., A^(2n-1) B}? Talk about bad notation.

1:31 AM

@rcollyer I actually didn't find that all that confusing (and I may have seen something like this used in literature/books too)... also, it's not a list of matrices, but matrices concatenated along the rows (i.e., take the second, insert columns to the right of the first and so on). The | are supposed to indicate columns

I think he has his dimensions for Q flipped around

2:23 AM

#CHM: thanks (for the links in reponse to web apps with Mathematica)

@chm: ^

3 hours later…

5:11 AM

Is there a more idiomatic way to say : Table[{i, j}, {i, 1, 9}, {j, i+1, 9}]

5:34 AM

@term-rewritica That seems pretty idiomatic. Did you mean for the last row of your table to be empty?

Or did you mean Table[{i, j}, {i, 1, 8}, {j, i + 1, 9}]

6:30 AM

@sblom Lazy people like me sometimes do Table[{i, j}, {i, 8}, {j, i + 1, 9}]

Anyway.. we're the record holders for the SE site with the shortest beta phase EVER, yes? :)

@J.M. =)

@term-rewritica You're welcome.

@CHM: why are the $\pi$-electron clouds colored differently? :)

@J.M. look at this

It's called a "Jelly Benzene"

Made by Richard Terrett over at Chem.SE

...now, how do I fake gelatin in Mathematica...

hi all, @J.M. I'm not sure if that's true - they used to consider graduation at 90 days? But we were definitely the fastest ever to beta, except possibly Ubuntu.

6:39 AM

@CHM I'd sure like to see "jelly ferrocene" myself...

@Verbeia Oh well, it can't get rid of that warm fuzzy feeling I have for this site... :D

@J.M. me neither. It's just a pity I've been travelling this week. The site looks great on the iPad, but I haven't been able to contribute anything.

If I don't get my act together belisarius is going to ovetake me :) and I had a head-start on him (belisarius didn't join the beta on day one)

@R.M FWIW, I'm back to Python. Haskell was just... too much a waste of time - for my current purpose. Forget IO with it until you're pretty damn confident in the language - not even the interpreter can help with that... And I had a horrible time trying to set up GUI packages. Python is a lot more nice to me. He doesn't whine all the time.

I'll get back to learning Haskell once I'm done with this project, when I can actually profit from it.

@J.M. Hehe. Well, someone might make a fortune selling "chemical candies"

@CHM It's usually not a good idea to simultaneously learn a language and then use said language for your actual work. I've found that you often get mixed up if the difficulty(ies) you're encountering are due to the language, the actual problem, or both.

@J.M. Oh, trust me, I didn't get mixed up - the difficulties are inherent to the language.

@J.M. I agree - though certainly using a language in your actual work is a good way to get better at it (as is answering questions here)

6:47 AM

I mean, I've only dabbled in Python - nothing serious yet. I had to decide on which language to use to translate a MMA program. Was suggest Haskell, because I thought my life could be easier with pattern-matching.

But...

My time hasn't come for Monads yet. I just want to write this crap - forget beauty - and get on with other things xD

@Verbeia True. What I'm saying is, get a "feel" for the language first (which, unfortunately, might take long, what with the learning curve and all), and then apply said language to your actual problems.

@CHM "I just want something that works; I don't care if it looks stupid..."

@J.M. That's what "updates" are for ;)

@CHM I agree, but I should remind you that it's easy to fall into the trap of producing a Rube Goldberg if you aren't careful.

True.

See that's what I find bizarre about Python - how linear it is

Which makes my scripts look like Rube Goldbergs, indeed

Now that's what I'm talking about! No need to learn tons of new concepts. Install, copy/paste code, run. Details can wait.

2 hours later…

8:39 AM

I suggest we DO NOT delete this question:

1

Q: Is there a way to undo multiple changes in Mathematica?

Possible Duplicate: Implementing efficient multiple undo Is there a way for someone to undo multiple changes in Mathematica?

It's a Google gateway to the site, and it's more likely to be found by people wondering about multiple undo. Let it be as a closed duplicate.

I'd also like to draw attention (again) to this link: mathematica.stackexchange.com/tools

With graduation and rep threshold increases, the community moderation power has somewhat decreased. Those of us with 10k+ rep should visit this link more often (@Vitaliy @kguler @Rojo @Jens)

3 hours later…

11:43 AM

@Verbeia Should my rep get close to yours someday, I will start giving away bounties to respect your age.

2 hours later…

1:22 PM

@CHM I learnt Python for a specific application by programming something I needed. I agree with J. M.'s advice in general but Python is so simple to learn that I think you can just dive right in. However, I believe my Python style is quite nonstandard which is both a product of Mathematica and the fact that I don't like the standard style (I think it's too procedural and verbose).

1:33 PM

Notification bars are blue. And it's bloody annoying when the question gets deleted in the middle of writing an answer.

user image

It would have been valuable to at least mention SolveAlways.

Wow. Yes, annoying. Personally I think if you're writing a question as it gets deleted, the system should at least let you post the answer you would have given.

It's good it told me about the deletion easrly and it didn't let me finish the answer.

@@math-visitor check out SolveAlways, you may find it useful

@R.M. So self-deleted questions don't appear in the recently deleted list‌?

Hm. No more moderator tools for me. That's a bit annoying.

@Szabolcs I agree, leave it be

Incidentally, I am amazed that the usual nonsense about it being difficult to implement undo in mathematica hasn't been spouted here. Another advantage over the mathgroup!

1:52 PM

@szabolcs no

@R.M In the case of that deleted question in the screenshot above (I lost the link), I don't think it's the same as his previous question. I'd use different methods (not string replacement).

I didn't ask him to delete... Just to try along the same lines and show us his work

Someone did ask him to below your comment. Perhaps that's a bit too harsh. I may have missed some discussion though (maybe he solved it on his own).

I'd waita bit... He's either solved it or will try it and posta new one

Ajasja did, but he had a second comment thatsaid he didn'trealize it could be done via string replacements

You want a link?

no no

Do you think it'd be appropriate to make an ad for the image uploader? I want more people to test it. I got no feedback at all about the new version.

1:59 PM

Go ahead... That's what the ads are for. I did not know there was a new version. In fact I haven't been usinge it because the last thing I remember is you telling that there were problems with it on mac

@R.M For the basic use case (select an image, press the button, upload), it work well on Mac. The problems appear when you change the zoom factor or try to copy very large expressions verbatim. Actually the "problem" is that it strips non-standard styles, resets magnification, and reformats everything to about 600px wide (to fit an SE post). Otherwise it works fine.

morning

all

Hehe, I do all of that... Non standard styles, zoomoing before saving, etc

Morning, @bel

One quick q: What is the simplest way to use state-preserving variables in a function?

contexts?

That would be one... Also see "Advanced uses" under Module here

40

A: What are the use cases for different scoping constructs?

You will find a lot of information in this answer. I will add a few personal notes. Module Use Module when you want to localize variables inside your function`s body, and those variables will potentially acquire and/or change their values during the computation. Basic use For example: f[x_]:...

2:14 PM

@R.M Thanks! I'll take a look

21

A: Functional style using lazy lists?

One way to get the lazy aspect is to use a closure, or the closest way for Mathematica to fake a closure. This is the closures constructor: makePalindromePrimeC[start_: 1] := Module[{p = Prime[start], r}, ((r = NestWhile[NextPrime, p, With[{d = IntegerDigits[#]}, d != Reverse[d]] &...

@Szabolcs pretty sophisticated :D

@belisarius You'll find some uses here as well.

2:41 PM

darn repcap

1 hour later…

4:02 PM

How do I write a bullet list in a notebook?

4:12 PM

@Szabolcs In standard style-sheet go: Format>Style>>Item and of course you can apply this simultaneously to a group of cells

@VitaliyKaurov Thank you! So all of these items need to be separate cells then.

@Szabolcs yes

I added an update check button to the image uploader. If you find any problems, let me know! Would it be too aggressive to add an automatic update check every few days? Some people might get upset.

what is "automatic update check" ? @Szabolcs

@VitaliyKaurov I want people to always run the latest version of the palette, so bugs are found out as soon as possible. Right now I added a button which checks the version of the palette on GitHub and compares it to the installed version. The button lights up in light red if there is an update (as a reminder). I was wondering if it would be too aggressive to run the update check in the background automatically every few days instead of waiting for the user to press the button.

If there's an update, they'd notice right away from the reddish colour of the button.

4:20 PM

@Szabolcs I think it si worth trying and seeing if people complain

Also, the palette source code is getting messy. I'm not used to larger projects... It could use a review. I'm not sure if I'm doing everything the Right Way.

can u send me a link to it? @Szabolcs

I should clean it up and comment it a bit more first though.

Sure, let me know.

43

Q: Can I easily post images to this site directly from Mathematica? (Yes!)

Graphics are tightly integrated into the Mathematica interface. The Front End is programmable, and Mathematica has functions to interface with the web, so the question naturally comes up: Could we make it possible to upload images to StackExchange directly from Mathematica, using a palette butt...

support faq site-tools

4:22 PM

@Szabolcs ok thx! gtg ;-) I'll take a look when have some time, O&U

Thanks :-)

4:41 PM

@OleksandrR. Yeah--very frustrating. Every beta user should get a 5x applied to their rep upon graduation. :)

5:04 PM

@sblom well, I don't care about the points. But not being able to easily find deleted posts is a bit of a nuisance. Had to change my icon too as the last one clashed horribly with the new design. Not sure the new one is too clear. :)

1 hour later…

6:11 PM

@OleksandrR. Hehe. Procedural programming is what comes most naturally to most people, I guess. It's how we're made : you don't often see a car mechanic "applying" his "repair function" to a broken car xD So it would seem natural to think in a procedural fashion... unless you train yourself not to, at which point you can benefit from FP. But Haskell's not a language you can learn over a weekend and hack something together quickly - Python is.

It's something anybody right-of-center (in a bell curve) can pick up with a couple coffees and a goal in mind.

Helloo

Question

From the More Information section of Covariance

For a matrix m with p columns, Covariance[m] is a p*p matrix of the covariances between columns of m.

On a similar note - I'm profoundly disappointed by how CS/IT were taught to my generation (I left HS 4 years ago). We were formed to become users, not masters. Forget about programming, other people can do that: you're gonna learn how to use the whole Office suite, how to draw nice pictures in MSPaint, and if you're really into it, maybe write your own HTML website with JS visitor counter - but that'd be quite unorthodox.

From the More Information section of Correlation

For a matrix m with p columns Correlation[m] is a p*p matrix of the covariances between columns of m.

@Rojo what's the ouput of both functions on a small square matrix?

Now, the correlation docs probably meant the correlations between the columns

Correlation[ {
{a, b},
{c, d}
} ] outpus

{{1, ((a - c) (Conjugate[b] - Conjugate[d]))/(
Sqrt[(a - c) (Conjugate[a] - Conjugate[c])]
Sqrt[(b - d) (Conjugate[b] - Conjugate[d])])}, {((b -
d) (Conjugate[a] - Conjugate[c]))/(
Sqrt[(a - c) (Conjugate[a] - Conjugate[c])]
Sqrt[(b - d) (Conjugate[b] - Conjugate[d])]), 1}}

6:18 PM

From those definitions, it should be the same lol

It's normalized... Covariance is not

{{1/2 (a - c) (Conjugate[a] - Conjugate[c]),
1/2 (a - c) (Conjugate[b] - Conjugate[d])}, {1/
2 (b - d) (Conjugate[a] - Conjugate[c]),
1/2 (b - d) (Conjugate[b] - Conjugate[d])}}

Rojo - Correlation[{{0,1},{1,0}}]

Ah.

In[2]:= Correlation[{{0, 1}, {1, 0}}]
Covariance[{{0, 1}, {1, 0}}]

Out[2]= {{1, -1}, {-1, 1}}

Out[3]= {{1/2, -(1/2)}, {-(1/2), 1/2}}

Indeed.

@Rojo Wait, you mean Correlation is not normalized, and Covariance is?

@CHM No, the other way around I meant

Correlation always seems to have 1s in the diagonals

But then look at my example

@CHM Your Covariance has 1/2 on the diagonals, and hte correlation has 1s

It's ok, I think I know what it does... I was also having trouble because Correlation was taking TOO LONG for a 7000x7 matrix, while Covariance wasn't. But I just realised that the matrix had integers in it

Now both are fast

6:23 PM

ok

Thanks

0

Q: The 'X' button when voting to close isn't centered

If you click 'close' on a post, the X in the button to close the popup isn't centered in the circle: OS X 10.6.8, Chrome 20.0.1132.57

Try N@ if there's a normalization step involved. See if it's faster

It should be... At least in my programs it is.

Where are you from @CHM?

Canada.

Maybe I should have mentioned that in my rant up there

Education is obviously different from place to place.

6:25 PM

Way faster

Did you ever see How I Met your Mother?

@Rojo Heard of it. Heard good of it.

Yeah, it's good. One of the main characters is Canadian and they make jokes about it. I was intrigued as to how they were received by another Canadian, hehe

@Rojo I don't mind humor. Some people do, I guess it doesn't really have to do with nationality, but rather how you were brought up.

Sure

You are pictured as very nice people anyway

and they also messed with Argentina

in some weird way

The canadian girl had moved to Argentina for a few months, and then went back to USA with an argentinina boyfriend

Heh. Well, I live in the French speaking part of the country. We're even nicer ;)

Most people here don't introduce themselves as Canadians, but as Quebecois. But anyway.

@Rojo And you are from Argentina?

6:31 PM

Salut!

Yeah, I've always lived in Argentina

That Argentinian guy was played by a NOT argentinina singer Enrique Iglesias... And they portraid Argentina as anything but what it is... Beach, people playing drums on the street, huge nonsense

Bien, bien.

@Rojo Anybody educated would have guessed.

Bien bien peut être français ou espagnol

Je ne me rapelle beacoup de français

:)

Jaja.

Hablo un poco espanol tambien.

¡Muy bien!

Tengo amigos en la Universidad que hablan espanol, son de Ecuador y Colombia.

Necessito practicar con ellos ;)

6:42 PM

Lot's of countries speak Spanish so it's nice to know

@CHM I think probably the motivation for that is that these are basic skills expected by all employers. If the student is motivated, they can teach themselves to program (or wait until they reach university). On the other hand I do regard classes such as you describe as largely a waste of time--if someone is unable to figure out how to use Word or Excel for themselves when they see it, they're never going to be very competent with it anyway, so might be better off doing something else.

@Rojo If my memory's right, it's the second most spoken language.

In this chunk of Universe, at least.

@OleksandrR. Haha.

The other way around, though, is much more satisfying: if you can write programs, then you can surely use Word.

I had a young teacher in HS who was doing his Master's in AI. He had set up a nice course syllabus over the summer: we would build our own computers from parts of old ones the school was supposedly throwing away, and then install Linux and write some batch scripts.

@OleksandrR. In the mains, I have to agree. There is something to be said for more advanced classes as there are some neat tricks in Excel, but you can get them from books, too.

We never got past the "build your own comp" section. He installed linux for us on all of the computers over a weekend, making sure everyone had a copy of UT, and we spent the rest of the year playing UT three hours a week.

Makes for good memories, but it was empty pedagogically.

@CHM That's how my programming class in HS went. She figured we would do better learning it on our own, and I and several others finished most of the years course work by Christmas. So, we played games, lots and lots of games. Of course, these were 286's so there was no such thing as speed.

BTW, I like the new gravitar.

6:56 PM

@rcollyer Ha! Pong?

Thanks. Credits to the author are on my profile.

@CHM Yeah, I saw it when he posted it.

@CHM no, Scorched Earth.

Never heard of it.

Scorched Earth (video game)

Scorched Earth is a popular shareware artillery video game, which is a subgenre of strategy game. The game was developed in the DOS era, originally written by Wendell Hicken (using Borland C++ and Turbo Assembler), in which tanks do turn-based battle in two-dimensional terrain, with each player adjusting the angle and power of their tank turret before each shot. Description Scorched Earth is one of many games in the genre of "turn-based artillery games". Such games are among the earliest computer games, with versions existing for mainframes with only teletype output. Scorched Earth, with ...

@OleksandrR. by that argument maths shouldn't be compulsory at school, though (not that I have an opinion either way)

Got to run. Bye.

7:21 PM

Me too.

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