@halirutan Hey, I only saw this yesterday. Thanks for the code; my current Gravatar was built from it.

@J.M. It's really funny because I saw your new gravatar and checked your user profile to see a larger version.

There I found the reference to me and I thought, ok...? I never posted knot code.

But now I see it.

BTW: it's not a Texture[]; I remapped the polygons generated by your routines to parameter values for the knot; those are actual colored Polygon[]s.

@J.M. I would have expected nothing less ;-)

@J.M. Has some black pixel in the upper half?

@halirutan Must be aliasing... I was too lazy to run the antialiasing snippet. Let's try again.

I noticed that two meta questions I asked show up in my "Community Bulletin" panel. Does everyone see the same "Community Bulletin" contents?

@GeorgeWolfe The questions displayed there are picked somewhat randomly from the recent questions.

Thanks

I have a quick question for anyone who would care to answer. How can I figure out what the structure of a particular object is so I can design functions that can take those objects as input or create those object as output. For example, I want to create my own edgerendering, vertexrendering etc functions for layeredgraphs.. but I don't know how a graph is stored mathematically, is it like stored like a n-dimensional matrix where some dimensions stores something?

Is there a command in mathematica which would tell me the structure of various things

@Amatya InputForm[] and FullForm[] would be useful for looking at how a Mathematica object is structured.

@J.M. cool thanks. Lemme go check it out.

@J.M. So I did InputForm[{1->2}] and FullForm[{1->2}] and the former told me how to input it while the latter told me List[Rule[1,2]]... the latter was helped some but I'm still not sure if the graph is a 1-D Matrix with 3 entries {1,2,->} or a 2-D matrix with{ {1,2},{1,0}} where the second row captures the direction of the arrow.. or some other structure

Look at Graph[{1 \[UndirectedEdge] 2, 2 \[UndirectedEdge] 3, 3 \[UndirectedEdge] 1}] // InputForm

Graph[] doesn't store adjacency matrices internally, if that's what you're actually asking.

@J.M. ok that really helped. So it is two arrays of whatever lengths. The first stores the vertices and the second stores the relation.

by whatever i meant varying

I don't know what adjaceny matrices are. I just want to be able to define functions on things and to be able to do that I need to know what they look like mathematically and I am having trouble figure that out and hence the question

@Amatya The second list is the list of edges, yes.

@fpghost That's straightforward: wrap the code inside the Module in InterruptingCheck. It has the same form as Check, but stops execution by altering how a Message behaves.

Szalbolcs had an alternative that uses internal, undocumented functions to accomplish the same thing. Also, worth a read.

@J.M. Still here??

hi

@belisarius Hi

@halirutan Hi Hali! How are you?

Ready for bed. It's 5:04 here ;-)

@halirutan What part of Europe?

@belisarius Yep. Let me show you smth..

Have you read this question here?

@halirutan Hmmm I think it was much shorter when I read it

I added some extra information. But that doesn't matter.. you know what this is about and thats enough ;-)

I think I made some real progress tonight.

Look

and abracadabra..

And all this without explicit tokenizer.

Still needs a lot of work, but not now.

I have a "subjective" problem with that kind of questions. And I MUST remark the subjective part

What is a subjective problem in this case?

I think a language should publish its grammar

and WRI doesn't do that

so you're bounded by your interpretation

of the language

Yes, I completely agree with you.

This isn't a critic. Just an observation

Ok, I think I'm out for a few hours of sleep.

Good night all.

@halirutan "a few"?

till 9

makes aehm

3.75 h

I remember many years ago, when I started learning about computers, reading a manual from Apple with a formal grammar for the Basic Language. And I thought ... How those guys spend time doing such a stupid thing for a simple language

Two years later I was writing an interpreter for that stupid language to port a set of programs to another platform

@belisarius Has no one ever tried to ask WRI wether they can publish their grammar?

Thanks god (or whoever took the decision) I was able to do that because of that stupid manual

Maybe a formal grammar was never written down.

@halirutan AFAIK, WRI makes a cult of secrecy

@belisarius Hmm, too bad.

@halirutan Anyway, my CST isn't strong enough to identify what kind of grammar they are using

but probably it's fairly difficult to parse

The pure functions are likely to be a mess

@halirutan Not only that. As it's a term-rewriting language, the parsing is dynamic in (at least) two ways

at scan time, and at execution time

AT LEAST

any valid expression comes invalid after the evaluation of another expression

@halirutan Now I am.

@rm-rf Hi toad! haven't seen you.

I think you pinged me earlier

Have I said I love it?

@J.M. Just wanted to show you this

and then go to bed ;-)

@halirutan Neat!

@belisarius Inhale... exhale...

ok, now really g8.

@J.M. I can hear it. Am I seriously compromised?

@belisarius I'm pretty sure that's something only you can answer. :)

@J.M. My fourth shrink used to say something similar. Well, perhaps it was my third wife. Anyway

@belisarius You're sure you didn't marry your shrink? ;P

(FWIW, shrinks are on my "professions I'd not take girlfriends from" list...)

@J.M. I'd never do that with such a lame person

@belisarius Okay, just checking. :)

@J.M. No difference. A gf will behave as a shrink, no matter what she studied

@belisarius Hmm, maybe. If my last one did put herself in a "shrink" role, she sure did a good job of hiding it...

@J.M. "Why do you stare at me that way?" ... sounds familiar?

@belisarius Well, not exactly that... "Just looking at you makes me feel better." The googly eyes may have been concealment, I guess.

@J.M. had you read "The Citadel" from Antoine de Saint-Exupéry?

Sorry, I'm uncultured these days. :D I never read anything else from him except "The Little Prince".

@J.M. "The Citadel" is his last (unfinished) book. There is a story about ... let me search for the quote. Wait a second

@belisarius Oh, yes. Did you add and delete a comment on the blog today (with your silly breathing logo)? I ask because I see it in the filter, but not sure if the spam filter caught it or you deleted it yourself

@J.M. And how does that make you feel?

@rm-rf :P

@rm-rf yup. guilty. I confess.

I swear, those psychology students I've seen can't do any other voice except monotone...

@belisarius Ok, just curious because I'm still poking around the spam queue and wanted to make sure I didn't mess with something :)

@J.M. I've had a psy gf when I was at uni. Not monotone, I can assure you

Is that one with depth?

@belisarius lucky you...

@rm-rf Yup, I made the logo solid.

Neat! :)

(...then tweaked Opacity[]...)

It doesn't breathe. it shall die

I just ran ThickenPolygons[] (from here) on it, actually. Worked like a charm.

@J.M. Here is the quote

page 332] "More dangerous still is the 'sect' of those who have a mole on the right temple. And, in our innocense, we never gave them a thought! Which means they hide themselves yet more cunningly.

Most dangerous of all is the 'sect' of those who have no mole on their faces, for clearly such men disguise themselves, like foul conspirators, so as to do their evil work unnoticed. So, when all is said and done, I can but condemn the whole human race — since there is no denying that it is the source of all manner of crimes; rapes and kidnappings, embezzlement and treason and public acts of indecency. And inasmuch as my police officers,

besides being police officers, are men, I will begin my purge with them, since 'purges' of this sort are their function. Therefore I order the policeman who is in each of you to lay hold of the man who is in each of you, and fling him into the most noisome dugeon of my citadel."

Which is the most dangerous gf?? eh??

she ... who doesn't look like a shrink

QED

@J.M. You should skim through this. Very interesting doyletics.com/art/wosart.htm

@J.M. This is a masterpiece, from the same book

[page 90] Thus I made answer to my generals when they came and talked to me of "Order," but confused the order wherein power is immanent with the layout of museums. . . . my generals hold that those things only are in order which have ceased to differ from each other. Did I let them have their way, they would "improve" those holy books which reveal an order bodying forth God's wisdom, by imposing order on the letters,

as to which the merest child can see they are mingled with a purpose. My generals would put all the A's together, all the B's and so forth; and thus they would have a well-marshalled book; a book to the taste of generals.

I've read it in Spanish. The translation was far better

@belisarius Good points...

@belisarius Well, I'm guessing the original French had a lot of curlicues lost in the English translation.

...anyway, for those who want to play with the solid logo:

Graphics3D[Rotate[ThickenPolygons[
       Prepend[DeleteCases[
          p7 /. triangulate /. moretriangles /. shrink /. shrink /.
            shrink /. colour4["SunsetColors", 1, 28/34],
          Polygon[l_] /; Length[l] == 3, Infinity] /. v_ /; VectorQ[v, NumericQ] :> Insert[v, 0, 2], EdgeForm[]], 1.,
       1/3], -Pi/3, {0, 0, 1}], Boxed -> False, ImageSize -> Full,
     Lighting -> "Neutral", ViewPoint -> {2.5, 2.5, 0}]

Hi @verbeia could you please contact me by email linked to my account?

@VitaliyKaurov I don't have sending capability for a couple of hours but if you search on my username you will find my website. There is an email there you can use to contact me on, remembering I'm not called Ted.

hi: quick dumb question: how does one zoom a cdf file within a browser? (fonts are much too small for my screen).

@rcollyer thanks a lot, I will give that a go

@Verbeia thanks, will do!

@Verbeia how often do you get mistaken for Mr. Ersek? :)

@rm-rf just wanted to update on the planned blog - seems like I´ll just finish the whole thing and air it on saturday or sunday. Cause of the NDA a lot of the interesting stuff can´t be posted ;-(

Otherwise the increments will be not so relevant and people may not come back to look at the rest...

@YvesKlett Damn NDAs... :(

@J.M. buggered stuff. Lotsa interesting things here.

What's left to write about, then?

Sore point. I´ll try to get more mugshots.

There are several interesting talks not to do with V9.

Ah, I guess that's small consolation...

To anyone seeing this and being in Champaign - meetup at 11:30 at registration for merry group photo!

@J.M. can I ping a whole bunch of users in one go?

@YvesKlett IIRC there's a limit. How many?

@YvesKlett ah, damn :(

@rm-rf we would need a sock puppet :-)

@J.M. as many of the top users as possible - they are difficult to herd here and without e-mail it is even more difficult.

@YvesKlett Eek, I thought you were going to type in their names one-by-one; I don't believe en masse pinging is supported.

@J.M. oh, eek indeed.

and the auto-completion does not work for all users ;-(

@J.M. do people get a notification if I ping them in any case?

@YvesKlett Supposedly.

o.k. I´ll start spamming. Sorry for that.

@J.M. How long does it usually take until an avatar changes after setting it at gravatar?

@halirutan Takes two minutes, tops, for me.

@halirutan and he should know about hi-freq avatar changes.

@YvesKlett Hey, I only molt weekly! :)

@YvesKlett Yep, ...

@YvesKlett So you are all at the tech. conf at Wolfram? Did you take @ruebenkoe with you?

@halirutan: No have not seen him yet ;-( I expected to see him around.

@YvesKlett if you see him, give my regards to him. And to Rolf..

And now I'm sad.. I would really like to meet the other guys in person.

@J.M. And there is my new avatar ;-)

@halirutan you should start organizing funds for next year. It is really a quite enjoyable conference

@YvesKlett I just don't enjoy traveling very much, the money was available in my project budget.

Maybe next year I force myself..

@halirutan We´ll drag you screaming over here. Although I am not really jetlag-proof myself.

@J.M. Most probably not... half of them haven't been in chat in a long time (DL probably never). Unless of course, you converted them all to @@ ;)

@YvesKlett Coool!

@Murta hey, one at least!

@halirutan I quite like the shirt. :)

@YvesKlett well it helps that I'm sitting in the same row as you, and you never even noticed ... :p

@J.M. That was the intention ;-)

How does Mathematica's NDSolve stack up against C code for solving ODE's these days? would something like GNU-gsl be much faster at getting the solution?

all: I have something like

{0, 0, 0, 1, -1, 0}

(ie a list of lots of zeroes, a single 1 and a single -1)

I want to test if the 1 and -1 are next to each other; what's the fastest way?

@acl Only 0, -1 and 1?

@belisarius yes, that's guaranteed

lemme think

ONLY one -1 and ONE 1?

@belisarius yes, one of each

exactly one of each

@acl MatchQ[{0, 0, 0, 1, -1, 0}, {___, 1, -1, ___}]?

or MatchQ[{0, 0, 0, 1, -1, 0}, {0 ..., 1, -1, 0 ...}]

@J.M. thanks

I have an compiled (very ugly) thing that does it reasonably fast

@acl How big is your list? Are you still trying to squeeze speed out of it?

Can the first and last elements both ever be 1/-1 (i.e., {1, 0, ..., -1})? If not, I have a fairly fast method

@rm-rf hm yes

2^L with L as large as possible, given that the final result of all this is a 2^L by 2^L matrix

@acl ah, damn.

in any case, could you test the speed of this Length@Split@Unitize@list <= 3 against your compiled code for a case when both the first and last are not non-zero?

If it is still pretty fast, then the lone exception can be special cased

@rm-rf that's a good point

@rm-rf ok let me do that when the current run finishes

hm didn't think of this; maybe it can be compiled

@acl Sorry. Got a phone call and had to go

@acl btw, how large can L be?

@rm-rf as large as I can get it

so basically I am constructing a matrix, using something like

SparseArray[
 {
  {\[Alpha]_, \[Beta]_} \[RuleDelayed]
   matrixElement[\[Alpha], \[Beta], sites]
  },
 {2^sites, 2^sites}
 ]

and this matrixElement is what I am trying to speed up. but, as you can see, this matrix is 2^L by 2^L (sites is $L$!), and I need the full spectrum, so the bottleneck quickly is Eigenvalues

but anyway, I am just trying to find my way around this right now, so it doesn't have to be as fast as possible

@acl Ok. Well, I was thinking that FromDigits[Unitize@list,2] would give you a number that is of the form 2^n + 2^{n+1}, for 1 ≤ n ≤ L-1 if it fits your criterion. You could just have a function with downvalues memorized so that f[number] = True and False otherwise

@rm-rf that I also tried

or something similar anyway

(converting to binary is an obvious thing to do given the interpretation of what I am doing)

or just f[possibilities] := True

@rm-rf if the number is small enough. I hadn't thought of that

the way it is now I am basically limited by memory, so I think I'll leave it like this

but, I am a bit worried about how accurate the eigenvectors are

ok anyway I am interested only in a subspace of the space spanned by those eigenvectors and I can project there before doing anything, which makes the size of the matrices much smaller. so I think I'll just switch to that

it's too ungainly this way

thanks for the help to all 3

:)

No worries :)

Sigh...

@acl How fast is this Cases[Differences@{0, 0, -1, 1, 0, 0}, 2 | -2] != {}

He's sure gonna ask another "Best practices question"

@rm-rf I found that rather insulting

was going to flag it

@belisarius Me too. I was also livid because if insulting the first time was not enough, he came back 10 hrs later (before a response from magma) and clarified that "In case you misunderstood, I was pissing on you"

but ... seems like throwing fuel to the flames

@rm-rf omg

that's trolling

@belisarius Well, I'm paraphrasing liberally... :D

you are too creative

I thought you deleted that comment

The comments there are all there is. I'm just letting you know how it sounded to me :D... I was busy today and didn't have time to look at the package to see if it warranted such criticism (not that I understand anything of category theory), but I'm glad Simon commented

@belisarius fast!

thanks

@acl I'm sure there should be some better trick. I'm processing the list twice there

@acl FreeQ might be faster yet (I have an impression that Cases is the slower of the lot)

@belisarius yes

@rm-rf yep, may be

that could be

Hey

@rm-rf it's an autogenerated .m file. of course it has no comments!

and anyway, even if someone's code is junk, anybody who says "this is crap" to his face, in a public "place", is either trolling (ie, trying to wind people up) or has serious problems adjusting to society (or a third possibility is that they get regularly beaten up in their daily lives)