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00:00 - 04:0004:00 - 00:00

12:11 AM
Anyone around?
12:23 AM
just me , I guess
Hey magma
Hey Rojo
Que tal?
In Spanish we laugh with a "j" :P
All good, you?
Vives en Baires?
Sí, ¿vos?
12:27 AM
En Italia
Mi sorella es fanática de Italia :)
I never went
she is here?
No, sorry
In Brazil now
Hey, by any chance you understand well what Leonid usually means with the lack of mutable data structures and all that?
I will come to Baires sooner or later. I dance tango, so it's like a pilgrimage :-)
Tango is 80% for tourists nowadays
12:29 AM
what is your field of expertise?
I know, i know. But it is very very strong in Italy now. And most of Europe, really
I study electronic engineering, aiming at signal processing, but I still haven't finished so, no expertise yet :)
Did you try System modeler?
it is a very nice piece of software
Yeah, tried it, but
expecially with MMA
my month trial has expired and I didn't have time to dig in deep
I found it nice, though I don't know how it compares to similar software... You use it?
12:33 AM
you can ask for some extra time. i will do that too.
I almost did that yesterday
they now have a home edition
but instead, I opted for asking for a quote
so the price is more reasonable now
Because, truth is
I might use it during the next 6 months, but not in the next one
12:34 AM
@Jin Framed@Quiet@
Erosion[ColorNegate@(MorphologicalComponents@(EdgeDetect@#) //
Colorize), 3], "HSB"],
RemoveAlphaChannel@ColorConvert[#, "HSB"]] &@
@belisarius is that a virus?
@Rojo Jin colorized
It's nice to see he got the software, hehe
Haha, jin colorized
I gotta do something about my gravatar
@magma Did you use other similar software?
time to go to sleep. very late here. Good night
@Rojo I will pay you $10 if you let me make your avatar
and you use it after
12:37 AM
similar to system modeler?
@magma Yeah
@belisarius I'll give you a 10$ discount if I can reserve my veto
@Rojo no chance
@magma and what's your area?
like yours. i am an Electronic engineer
with a keen interest in pure math and physics
good night
12:40 AM
Night magma
@belisarius 10$ discount and I trust you for a day
@Rojo The making of an avatar is an artistic moment. You are betraying art and friends by being so suspicious
@belisarius Third world habits
A week!
Nahh ... making the avatar you deserve will take me more than a week. A full life, I believe, suffering the stressful state of not getting to perfection
12:47 AM
@belisarius Better than having Peron's face
@Rojo Bonavena's is not a bad idea
Grr, I just hanged my session while trying to do the most basic image processing ,I suck at that
12:53 AM
I'll never let go of my veto
you coward
and I still haven't let my imagination flow
@Rojo For example. You could try this for a week
just to find your real self
I'll put something provisional
circuits overload!
I love those four eyes
@R.M Those are three iconic Argentinian actors
1:03 AM
Now it's just one super iconic... thing!
@R.M Perhaps the woman is too iconic
Now, to change the picture I have to create a gravatar account?? I thought it was just uploading or putting a link
@Rojo yes. You upload at gravatar.com
Making your own avatar is a rite of passage
...and now.....
...how to link the gravatar account to this?
1:14 AM
If you've used the same email in both places, it'll auto refresh
The gravatar is linked to your email
We'll see tomorrow, I just put a plain red
If it updates, we'll see what's the definitive one :)
How creative!
You could Inset a Big "R" and win a Guggenheim grant
1:18 AM
Back, now it's updated
I did it in Paint
I'm looking to retag this question. Obviously, it shouldn't have as it is discussing std::vector not $\vec{x}$. But, maybe ? Maybe not.
@rcollyer I think C++, perhaps mathlink
c++ might be good... We have fortran, python, java, C#, etc.
That answers that. But, ? I don't think so. Nor, .
@rcollyer agree
1:22 AM
Any objections to my removing those to also?
, , , should be sufficient, I think.
why the last one?
it isn't output, per se.
I went by this paragraph:
> I want to store each of these vectors as a list in Mathematica, so, for instance, if three iterations returns the vectors (0, 1), (0.02, 0.9) and (0.04, 0.73), I want this output to be written into a Mathematica list of the form {{0,1},{0.02, 0.9},{0.04, 0.73}}.
I guess is more for NumberForm, etc.
1:25 AM
okay. 6 of one, half a dozen of the other by my thinking.
But, adding .
@Rojo now you look like the Soviet Union, or China. But smaller, obviously.
@OleksandrR. Yeah, I'm not liking it much. Too aggressive
@OleksandrR. careful, he may get an inferiority complex, and before you know it he'll be threatening Japan and the US. :P
@belisarius I would say more like a right nuisance! I'm not completely happy with my current one but it clashes with the site design less than the previous one did, so I can't be bothered to change it again.
@OleksandrR. :)
1:30 AM
@Rojo as I understand it, he's referring to the fact that in many cases, attempts to change a part of a data structure will result in the entire structure being copied and the part changed only in the copy, leaving the original unchanged. ReplacePart does this, for example.
Anybody knows how MaoTsé entered my monitor?
@OleksandrR. Thanks. What I'm actually interested in understanding well is, what does he(/you, etc) think would be nice to have. I've read so much about it that I want to give it a shot
and I trust his judgement on what's missing and would be useful
For example,
Having a function to "subscribe" a symbol as a copy of another, and a custom set that keeps both up to date when set
without having 2 copies of the data
and having the data remain on the other symbols if you clear one or set one with the regular Set
and no leaks
That would be enough?
Well, that sounds like it could be useful, but IMO the problem in general is more one of efficiency than semantics.
The thing is, I think that "that" could be done quite simply
Haven't tried it yet, but
if it worked, it would as inefficiet as MMA is in general
Yes. I understand where you're coming from, but it still doesn't buy you in-place updates. Built-in functions still copy extensively.
1:39 AM
Built-ins grr
So, in conclusion
For example, someone asked me a while ago if it was possible to do an in-place FFT. I didn't follow up on that but I am certain it is not without some serious messing with LibraryLink.
What he means is something that can't be helped as long as one can't make built-ins work in -place
I believe so, yes. Of course one can use things like linked lists which have much less to copy and thus have fewer performance pitfalls.
Yes, built-ins copy a lot, but
if you have a long list, say, "l"
and you do l+1
There is some object called a "raw array" which I believe is basically used when calling Fortran (LAPACK for example) because of the Fortran semantics. However how it works I don't know.
1:44 AM
You are right
You have RawArray, Dev`FromRawArray, RawArrayQ. Had no idea
So, list+1
or, worse
while it is evaluating, it uses up memory as if copying the list
but, does that imply it's slower that it would be in place?
Yes, right?
Because it doesn't mean it copies the list... Probably reserves the space and puts the results there
instead of in the original
I'm just trying to finally understand this big issue a little better
Well, that still involves a copy. It could update in place. Although, there aren't really semantics to express that.
Even the compiler copies extensively, it would seem.
I see that there's copying in functions that modify only a little part of a possibly long expression
such as ReplacePart
(which is one of the few that can be reimplemented in place)
(with part)
I think fundamentally it's hard to mix functional/term-rewriting semantics with mutable data structures without making a mess of things.
Part is one of very few exceptions...
I think even Part may copy in some circumstances though. For instance, when operating on a packed array.
So far, the limitation I really see is the one of not being able to extract a subpart of an expression (say half of a long list) without making a full copy of it
Yes, that's a major one. Of course you can use linked lists in that case.
Bags are also possibly useful in that they can be passed around like pointers to their contents.
1:53 AM
Any different from passing a Hold?
Well, you can destructure Bags without (necessarily) copying. Of course if you call BagPart[b, All] then it copies.
As I understand it a Bag is simply a very low level linked list.
... a linked list with heads that hold, that allows you to extract parts of it easily (not like a linked list), but doesn't let you remove elements
and that's actually an atom
which who knows why should I care
I'd consider that semantically the same as a Bag.
I was describing a bag
Oh, okay. :)
1:59 AM
Thanks for the Heap ;)
Did you make any use of it? I haven't tried, yet.
Not real use. Fake use, when I tested it a little bit
Heavens to Betsy!
Q: Integrate and NIntegrate problem

simplerexp := -5.082019443309081E^(-0.7036967536123101 (2/25 - (2 x)/ 25)) (E^(-0.11728279226871835(32/25 - (32 x)/25) - 0.11728279226871835 (2/25 - (2 x)/25)) - E^(-0.2345655845374367(17/25 + (8 x)/25)) (1 + 0.2345655845374367 x))^2 x (5.515552687747721\ E^(-0.23456558453743...

I'mi gonna upvote that
2:12 AM
It has been a long time since I saw a question that I am so glad to pass on
"I have a very long integrand,"
@Rojo Are you boasting?
@Rojo Hmm, I didn't mean it that way. But maybe this poster deserves it. :P
@verbeia shouldn't this be a comment?
A: Integrate and NIntegrate problem

VerbeiaIt's hard to work out the problem when the code creates syntax errors once pasted back into Mathematica. However, I would point out that you have some very long floating-point numbers multiplying exact numbers, all taken to the exponent. Integrate will use numerical methods anyway in that case. ...

@belisarius Rotfl
That formula is the nearest thing to spam maths could possibly be
2:21 AM
user image
must be a standard warning on any question longer than X
@belisarius would you please remove your comment on his question. Thanks.
@rojo My integrand is bigger than yours
@rcollyer Oh well, but I warn you Mma 9 has amazing new msgs
@SjoerdC.deVries Simplify will take care of that problem. :)
2:26 AM
@SjoerdC.deVries Too bad, it doesn't grow with x
@SjoerdC.deVries Depending on the method used, Integrate[exp ...], Integrated[Expand ...], Integrate[#, ...]& /@ Expand[exp], etc. I get different answers. So, I think she has the correct answer.
@SjoerdC.deVries I pity you then
It is actually interesting to ask you all
How big our integrands are?
No, not really, we have ladies in the forum
2:31 AM
;-D ;-D
How to know what's the form of an expression that leads to less numerical errors
That is an interesting question, and I wish I knew.
I'm not talking about integration any more
Horner form?
@Rojo don't work with exp(big number)... instead try to work with log and then take exp
2:32 AM
Is there an easy way for NDSolve to refine its range (ie make it smaller) based on a condition on the derivatives?
{y''[t] == ... && y'[t] > 0 ...}, y, {t, 0, 1}]
@R.M Why is that?
There was that question from that physics.se optics guy
There are two close votes on the question. What do you all think?
It's a bit specific
@SjoerdC.deVries three
3 votes, now.
2:36 AM
and phantomas
@belisarius no, it's mine! :)
@SjoerdC.deVries I think it is too localized.
Voted NaRQ. The integrand is a mess and Integrate's assessment of it is totally dominated by numerical error at machine precision.
and Mma::psycho, who was forced to left the party
yeah, but he's just no very constructive, or conducive to learning.
Hey, Sjoerd didn't even have to touch it.
@Rojo The exponentials blow up: Exp[10.^16] Exp[-10.^16] vs Exp[Log[1]]==1
2:40 AM
(For some strange reason, my mind keeps going into the gutter.)
@R.M Also, you're effectively using the series form of Exp which increases the number of multiplies dramatically. Even in Horner form.
@rcollyer The art of delegation...
In an unrelated issue, 100MBs is approximately the max bigint it's saving witout complainig
Q: Is it possible to make Mathematica reformulate an expression in a more numerically stable way?

Colin KI'm writing a numerical optimization, and I'm having a problem with an expression of the form $$ e^{-t} (1+\mathrm{erf}(t)) $$ The overall shape of the function looks correct, but when $t$ is small, $e^{-t}$ is huge while $(1+\mathrm{erf}(t))$ is very small, and their product is also small. This...

@Rojo ^
@R.M Niiice
@SjoerdC.deVries I figured. We're piranha and all.
And, someone chummed the waters!
2:43 AM
@rcollyer We must bully someone from time to time. If not, we risk eating each other
@belisarius as I said:
@belisarius Let's visit a Maple forum
4 mins ago, by rcollyer
(For some strange reason, my mind keeps going into the gutter.)
Anyone planning to go to the wolfram tech conference?
@Rojo or matlab.
2:44 AM
@Rojo Hey! That's a NICE idea
@SjoerdC.deVries I've been thinking about it, but I need to get funds for it.
@rcollyer R.M is about to write a blog post to evangelize Matlab users, and belisarius hates Maple
@rcollyer SE can do that

Proposed Q&A site for users of all experience ranges with Maplesoft's numerical analysis software.

Currently in definition.

@SjoerdC.deVries Can rep points be cashed ?
2:45 AM
@Rojo are there any? I wondered that the other day but was unable to find anything like what we have for Mathematica.
@SjoerdC.deVries that's true. Maybe a moderator should bring that up with the powers that be? :P
Let's joiiin
@rcollyer Jin said that they are fully aware of the conference and they do plan to send some members of the community
Q: How can I get Stack Exchange to send me to a conference?

Abby T. MillerI read Supporting Community Conferences, which states, Depending on the circumstances and location, we can also sponsor community leaders to attend an event on behalf of their site. We will subsidize your costs to attend, within reason, and provide you with a bunch of swag to use as an ice-br...

2:46 AM
1 follower, sad
@Rojo as long as you're trying to "save" the matlab users, then sure.
@R.M You are a professional agitator
Jul 13 at 3:10, by Jin
I'll have our community team make a meta post about this, to see who's all interested in going
Aarthi indicated that SE would indeed be willing to sponsor this
@rcollyer You used Matlab?
2:49 AM
I attended last year, fully self-funded and had to take vacation
@Rojo I was in a class where the professor demanded that we use it despite the fact that I copied the functionality we were supposed to use in mma in under a 1/2 hour.
Before I nominate myself to go, I'd have to check a few things.
I would like to attend. If you @All support my candidature I promise bringing back an autographed copy of NKS v2 for each one
(I really have to get my mind out of the gutter!)
Bring back a copy of v9 for us and I'll support you
You can either go to the conference or get v9... hmm. Tough choice
2:51 AM
I'm happy enough with the MMA9 documentation
All of us, every user with 500+ rep
I suppose v9 will be announced there
Let's hope
likely. depends on if they get the testing done and the features in in time.
@SjoerdC.deVries mmmm ... ok. I'll give you Maple v9 copy
2:52 AM
@rcollyer Unlikely that they'd be working on features now, no?
@belisarius aren't they on version 15 or 16?
@rcollyer No idea really
@rcollyer Maple9 is the latest in Argentina
Maple is at 16 currently.
That's matlab I'd say
2:52 AM
Uh, and we are at 8. Half
Meh. (old) Firefox vs Chrome, really.
I forgot, why is my name in blue here?
@R.M depends on a lot. If they're releasing in Oct., then putting in new stuff now would put them behind. But, they may just be announcing when it will be ready for sale in Oct.
I really have to get my mind out of the gutter
2:54 AM
@rcollyer That sounds more like Apple's strategy...
"World's most advanced OS, blappity blah Mountain Lion... coming this July" — announced in June
@R.M I have no insight into their strategy, so I'm just guessing.
I've heard rumors beta testing is underway
In beta features are frozen, right?
@SjoerdC.deVries They should be. But, not if they go the netscape route.
We could blackmail the SE team to force them to send all of us to the conference. If not, we will start posting the "long integrand" question on all sites
2:57 AM
But, being hellbanned from the entirety of SE wouldn't be worth it. We'd get more stuff done, though.
alright, gotta head home now.
See ya.
@R.M Auguri
@belisarius The meta post says "community leaders", which sounds sufficiently plural to me.
@SjoerdC.deVries true, but you have to define "leader."
2:58 AM
@SjoerdC.deVries communist leaders? Yes
@rcollyer Bye
@R.M Ciao
@SjoerdC.deVries I was saying bye to RM.
@rcollyer bye!
ohh my
@belisarius copy cat.
2:59 AM
Thunderstorms here
@belisarius Well, that hits my limit of not being able to respond due to it being a public forum!
So, good night all. I have to go beat on a cluster.
@rcollyer You shouldn't use your real name
Bye again
I am not saying goodbye again
3:01 AM
@belisarius So, your name isn't real?
@SjoerdC.deVries Ohh yes
This is me
Flavius Belisarius (, ca. 500 – 565) was a general of the Byzantine Empire. He was instrumental to Emperor Justinian's ambitious project of reconquering much of the Mediterranean territory of the former Western Roman Empire, which had been lost less than a century previously. One of the defining features of Belisarius' career was his success despite a lack of support from Justinian. He is also among a select group of men considered by historians to be the "Last of the Romans". Early life and career Belisarius was probably born in Germane or Germania, a city that once stood on the site ...
only younger
What's in a name
That which we call a rose
By any other name would smell as sweet.
Umberto Eco would be proud of you
Tell us more
3:06 AM
@SjoerdC.deVries Not if you called 'em stench blossoms.
I managed to finish Foucault's pendulum...
@SjoerdC.deVries I enjoyed the name of the rose a lot more
@belisarius The pendulum started ok, but the plot totally derailed in the final chapters.
@SjoerdC.deVries I've read "The name.." in two days or so. The "pendulum" took me a month
I forgot whether I read it or saw the movie
3:20 AM
@SjoerdC.deVries Oh ..the movie wasn't up to the book
@SjoerdC.deVries I thought it was too long. Can I even remove the answer once the question is closed? I posted it before others started commenting about numerical issues.
@Verbeia I was just wondering. Rcollyer thought it was Ok, and the point is moot now anyway.
@SjoerdC.deVries If the community feels strongly, I'm happy to remove it.
@verbeia that's not the case. So, no problem. You might want to scroll a few pages back to see the discussion that went on.
Getting some sleep now. Bye!
3:39 AM
@SjoerdC.deVries I just did, and I agree, this sort of code dumping should be discouraged.
But I think the way to encourage good behaviour is to tell them what they are doing wrong, and still give them some help, if not complete. If they are repeat offenders, by all means come down harder. But this user has another question with 10 votes, so I think they are amenable to polite education.
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