hi @newprint

Hi !

How are you ?

good. how did the exam go then?

(it was you who had an exam, right?)

Excellent, done with summer courses

Thank you for asking

I had two exams - Automata Theory & Num Analysis

had numerical today, Automata last Thursday

how does it work? exams every 6 months?

(where? US?)

I am in US.

It depends on the class

but in general

for each class, we have at least 2 exams

in general 3 exams

per?

Usual load for US students - 4 classes per semester

Semester is 3 months long

(One season)

so 8 exams per semester. not good for lazy people

Not only the exams, but homeworks, projects.........

workload is great

Are yourself in Latin America ?

no, germany now

Cool, I have relatives in Dortmunt (not sure about spelling)

I discovered now that I can access the branches of expressions in Mathematica, Is this common to programming languanges or is it a feature of some specific kind of languange or is it a feature only of mathematica?

@GustavoBandeira What do you mean with branches of expressions?

I've read the beginning of the SICP, and there they suggested that LISP also understands it's expressions with trees.

like trees*

Do you know the Level function?

@GustavoBandeira That gives subexpressions of an expression at a certain level.

Yes

That's what I mean with access the subexpressions - I took this from Leonard Schifrin's book.

I'm not familiar with LISP but I think it should be possible to access subexpressions of expressions in LISP as well.

I'm not sure if there's a specific function like Level fro it.

for*

Is this a feature of some specific kind of programming languange?

@GustavoBandeira I don't know enough about other programming languages to answer that question. I guess it's sort of possible with OO programming languages, or even a language like C which works with pointers.

Quiet in here today...

Yes. Hello.

@MrWizard Oh, hello. Lurking, eh?

Waiting for kguler .. if he shows up.

@kguler get in here! ;-)

I suppose you can use the dreaded "@@" if things get desperate...

That's what I just attempted; not sure I did it right.

Hello there. ;-)

Hi Mr.W

For reference, did you get the ping from this chat room or not?

Sorry it took me a while to find my way to the chat room

I just saw your message in the comments

Okay, no problem. I think I need to learn how to use the super-ping though.

Anyway, your solution looks great but the output isn't ideal at this point.

Let me give an example:

edges = {10 -> 6, 17 -> 18, 14 -> 11, 6 -> 13, 10 -> 9, 5 -> 14,
   9 -> 3, 1 -> 11, 3 -> 3, 7 -> 16, 2 -> 18, 8 -> 8, 6 -> 11,
   18 -> 10, 8 -> 15, 17 -> 15, 4 -> 6, 6 -> 1, 19 -> 6, 6 -> 4,
   11 -> 5, 18 -> 1, 18 -> 18, 19 -> 7, 14 -> 16, 2 -> 8, 10 -> 13,
   1 -> 14};

is the vertex set a range from 1- to-somenumber?

{1,{5,11,14,16}}

{1,{2,3,4,5,6,8,9,10,11,13,14,15,16,18}}

{3,{}}

{1,{4,5,6,11,13,14,16}}

{5,{11,14,16}}

{1,{4,5,6,11,13,14,16}}

{7,{16}}

{8,{15}}

{3,{9}}

{1,{3,4,5,6,9,10,11,13,14,16}}

{5,{11,14,16}}

{12,{}}

{13,{}}

{5,{11,14,16}}

{15,{}}

{16,{}}

{1,{3,4,5,6,9,10,11,13,14,15,16,17,18}}

{1,{3,4,5,6,9,10,11,13,14,16,18}}

{1,{4,5,6,7,11,13,14,16,19}}

yes.. as is, it works only for the case where the VertexList[g]=Range[k] for some k.

The groups are right, but the indexes are always the lowest number, so the output doesn't look good.

@kguler Okay try this: dat = Join @@ Position[#, 1] & /@ % then {#, DeleteCases[#2, #]} & @@@ Transpose@{Range@m, dat}

yes... it works great.

Perfect ... Now we can eliminate the ghost vertices (like row 12) at the last step.

Hello @imagedoctor

Mr.W thank you so much! I will edit the post with your suggestion.

@kguler Okay, great. Maybe I can find a cleaner way to do that; it's just the first thing I tried.

I was thinking about some edits to cover the general case with symbolic vertex names and work with VertexIndex, but I am not there yet.

@kguler Cool. @notify me when you are; I want to take a look.

I will... Thank you again for great suggestions..

@kguler better: {#, DeleteCases[#2, #]} & ~MapThread~ {Range@m, dat}

@kguler Check this out:

Pick[
  ConstantArray[Range@m, m],
  Sign@MatrixPower[N@%, m],
  1
]

Pick may be the right tool after all. :-)

@MrWizard, hi there, how is your day unfolding ?

@MrWizard, yess :)

@kguler Cookin' with gas:

Flatten@#@"NonzeroPositions" & /@
  SparseArray[pairs~Append~{i_, i_} -> 1`, {m, m}] ~MatrixPower~ m

@image_doctor Going OK, thanks for asking.

Hello @Arnoud

Hello, Mr.Wizard

Hmm... are those crickets in this room?

@JM Australian crickets?

Why Aussie ones in particular?

("crickets" was intended as an oblique reference to the relative silence of this room. ;) )

@MrWizard Glad to hear that, a grey overcast day here in the UK - but the tennis is providing some diversion.

@image_doctor By "tennis", are you playing it, or watching it?

@jm Mine was an oblique reference to Australian cricketers who are currently on tour in the UK, I think we may be dispersing the other crickets

It seems so, yes.

@JM Thursday is my day for playing tennis ... come rain, wind , snow or shine ... but as you rightly suggest ... it's armchair tennis today :)

...for a short while I thought "armchair tennis" had you using armchairs in place of racquets... :D

@JM lol... some more time in the gym might be necessary ... and I"m not sure what tension to string my armchair at ... :S :)

Also, it'd give a whole new meaning to "smash"... :)

@jm lol, the overhead "smash" sounds particularly ominous !

Hey guys... When you want to fit some data points, with whatever function

data as a list of {x,y} pairs

Does it take into account the density of data in different x values? Because my data is far from uniform and I'd like that to be weighted

@rojo that would depend on the function

@Rojo weights are all 1 unless otherwise specified.

@rojo SmoothKernelDistribution[] for instance would take account of the data density

@Rojo Fit[] on the other hand would not.

@Rojo If the weights are integers, you could, well, repeat the data points as appropriate...

On the other hand, note that LinearModelFit[] and NonlinearModelFit[] take a Weights option...

Hey, thanks a lot all

For now I used NonlinearModelFit and it's Weigth option, feeding it the inverse of the PDF of SmoothKernelDistribution from the data's x values

Maybe you meant to invert the CDF? :)

@JM, I want the less dense data to have more weight, I don't care if the x value is higher or lower... I guess that's with the PDF right?

With inverse

I meant

1/PDF

Not function inverse. I spoke horribly

The reciprocal of the PDF, then. :)

Mental note: 1/stuff is stuff's reciprocal

(...and now I understand what you're trying to do. ;) )

Reminds me of people getting confused between arcsine and cosecant...

Gotta go people. @JM, @OleksandrR, @imagedoctor, thanks all and have a nice day

I should be off as well. Later, y'all.

@Rojo good luck

@JM bye

OK.. so this question has been edited, rolled back and now re-edited, all for the same reason. Does anyone else think that it is actually a bug, and not just because Simon says so? (I haven't looked through the docs to see what the expected behaviour is... I'll do that later)

@Heike here we go with the achses again

@acl I'm afraid I'm missing the reference.

@RM I just read the email.

@acl Never mind, I just saw the question you're referring to.

@Heike must be the same person?

@acl Could be. We'll know for sure when he/she starts using equatations or whatever the term was.

@acl It is actually the same person: stackoverflow.com/search?q=%5Bmathematica%5D+achses

@Heike strange set of mistakes

@Heike that is a good point about Scale in your answer to the reflection question. I hadn't thought of that

@acl I only thought of it because the OP mentioned Scale in the question.

@acl That's what I thought. The repeated use of achses made me think that the OP was from a German speaking country but I don't think equotations is a German word.

@Heike the question is difficult to interpret

Tonight I realised how conditioned I am by Hollywood films. I was watching intouchables and kept wondering when the bad stuff was going to happen.

I badly miss the spaghetti western era

since we're talking about realizing things, tonight I went to a bob dylan concert. everybody was sitting down, quietly drinking beer after beer and eating sausage after sausage. I realized I had visualised bob dylan concerts differently.

@acl I wasn't even aware that he's still around.

@Heike well, when he started singing "all along the watchtower" it occurred to me that actually he comes from a completely different era. but otherwise, I don't really place him anywhere in time, like I do other musicians

I guess performing for 50 years must be getting old though

@acl Didn't he start when he was 18 or so?

I don't know, but he was performing before the beatles were famous. I think of the beatles as ancient (in terms of modern music).

@acl For me the Beatles aren't that old but that's probably because I mainly listen to 60s and 70s music.

@Heike I mainly listen to baroque music, but what I mean is, I don't think of the beatles as today's music. i guess it's just how we randomly file things and then they stay filed that way.

@acl I wish the Beatles were today's music. It would make the top40 much more enjoyable to listen to.

@Heike I had a period when I listened to the beatles almost obsessively, but now not so much

@acl I had that with Paul Simon.

@acl I guess most people go through that at some point... For me that was when 1 came out

@RM bit earlier for me I think. I still like their music but I think Dylan is different. I find his use of language incredible