@Verbeia I mean, each institution has its own mindset for writing those little art pieces. Some include a reference price and term, others enforce one, others lets you on your own. But they all coincide in a few nuisances. For example, you have to read 140 pages to understand if there is a predefined Go Live date or not
@Verbeia yeah :D I've read 100 pages to know that :D:D
@Verbeia My company writes RFPs for others, and we always insist about including an informal flyer with the relevant info for the proponents to understand quickly what is ging on inside the monstrous bulk of pages that follows
@Verde The main risk will be the "oh wait, can you also add this?" scope creep. They would rather take the time to do it right than set an arbitrary date. I really like the flyer idea.
Ok, lets give this a try. @Mr.Wizard already showed you, how you can use Interpolate to make a function from your discrete data and since you didn't provide some test-data, I just assume we are speaking of an isosurface of a function $f(x,y,z)=c$ which is defined in some box in $\mathbb{R}^3$.
...
whether it's possible to upload a large data file. Has someone an idea whether this is possible?
And what happened to the chat? I can not longer press enter to send a message and have to take the mouse??
@halirutan "permanently" is too much a word. that data is not that relevant, (it makes the question Too Localized. Get him to upload it somewhere, and that is it
Newer versions of Opera look just like Chrome by default. Personally I hate the modern fashion for how browsers look and behave, so I changed it, but I think if you were to install Opera you'd not have any difficulty in adjusting.
@Verde I looked it up once (because I'm naturally suspicious of people whose motives I can't discern...) but I forgot now; companies donate because they want a decent browser for their corporate users or something. Anyway what I remember is that they are doing quite well for themselves.
@halirutan I have the stackmma github account. I added you as a user to the attachments repo. If you find something you need to attach, please do so. Szabolcs is also on it and we've been using it for a few questions
@Verde you just need to write something else on the same line... it expands only if it's the only thing on the line
Here, on my Ubuntu 64bit with Chrome the chat does look very different from what I was used to see for a long time.
the right info-bar with the list of online users and the starred comments is completely gone.
on the bottom I have only a send button where there should be and upload button too...
Consider the following code which plots a triangle.
p = {{0, 0}, {.2, 0}, {0, .2}};
{Cyan, Polygon[Dynamic[p]]} // Graphics
Then adding ( for example ) {.1, -.1} yields a non-convex polygon.
AppendTo[p, {.1, -.1}]
Question: Given a list of 2D points that are plotted as a polygon by Graphi...
he has clarified (sort of) what he wants in the comments, and it's not what he actually asks, but I don't know how to express it well. it would be nice if this could be fixed rather than randomly upvoted!
MapThread::mptd: Object InterpolatingFunction[{{0.,6.28319}},{4.,7.,0.,{313.},{4.},0.,{1.},0.,0.,Automatic},{{<<1>>}},{Developer`PackedArrayForm,{<<1>>},{1.,0.999994,0.999978,0.99995,0.999911,<<42>>,0.956497,0.948089,0.946993,<<263>>}},{Automatic}][<<1>>] at position {2, 2} in MapThread[NIntegrate`InterpolatingFun
@J.M. What do you think of deleting Shog's default community ad in favor of cormullion's? I don't see a reason for two of the same ad which reduces chances for others
Please vote on this. It's an effort to get some unanswered questions answered (or cleaned up by editing/closing/deleting). Maybe we can also have a chat event to comb through the list and pull the weeds.
@rcollyer it is shown automatically, possibly to a random selection of visitors
@R.M ah. Right. I should post something on the blog, but the damned dissertation, death in the family, new job, and just life in general has made it very difficult to get anything done. :P
@Verde speaking of surrealism, I randomly ended up reading the following paragraph a few minutes ago:
Fernand Meysonnier is France's last executioner. Over the years, he has helped chop off the heads of 200 people.
In a small village in Provence an old man packs up a selection of terrifying torture instruments. This is M. Meysonnier, chief executioner until the guillotine was axed by the government in 1977. He performed his first execution at 14 and never looked back.
@R.M Per the prior conversation, today I spent trying to debug my install of LevelScheme` . The default layout is fubared, and I was trying to fix it. Guess what amount of work I got done today? :P
@SjoerdC.deVries actually, it wasn't meant as a harsh comment or sarcasm; I meant it genuinely... I also told him it ran smoothly on mine (didn't mention I fixed it) and that he should use PerformanceGoal -> "Quality" in case the slowdown he was seeing was due to plotting twice
@NasserM.Abbasi I'm not an expert, but I think this statement ("one is born an X expert, it's not a learned skill") generally doesn't apply to anything but the furthest extremes of performance
like Olympic athletes; no matter how hard I train for the 10km race, I'm not going to the olympics; but I can get much, much better at it than pretty much anybody who doesn't train
it's the same for less physical pursuits
it's just a question of motivation and organization (and of course being "smart" helps!)
the last few days/weeks, I am doing some exact calculations for quantum dynamics. that means you calculate some gigantic matrix (the hamiltonian), exponentiate it, and multiply the state vector by it. that's generically quantum time evolution. as you can imagine, doing this sort of thing for days loosens one's grip on reality.
one early morning, just after finishing work for the "day", it occured to me that, to the best of my knowledge, that's what the universe is really doing: multiplying two huge matrices! all our hopes, fears and dreams are basically artefacts of matrix multiplication!
well, it seemed funnier at the time, but I still think it's hilarious
(and funny for the same reason as those posters; it's true, actually)
@Verde right now? a lattice system which is driven with some periodically modulated force (I am trying to make some more general point and use this as an example)
basically trying to come up with something analogous to the Gibbs ensemble for non-equilibrium systems (ie, just unitary time evolution)
for closed systems
well, this is the main think I myself am doing the others in my group are doing other things which I just help with (in principle)
@Verde in fact, even closed, not driven but not in an eigenstate is interesting
if you have a two state system it's very easy to see how the time evolution goes; but take now some huge system, then it's not easy to see what will happen.
and "generically" what does happen is that each possible state i is visited with "probability" exp(-E_i/T) with T some lagrange multiplier (recall this is all unitary time evolution)
@Verde yes, actually, one question I always had since I was a teenager is, how come I can look at a glass of water and describe it so well with so few parameters?
well the basic insight is very simple, if the initial state is $|\psi(t)>$, and the hamiltonian has eigenstates $|u_n> with evals $E_n$, expand $|psi(0)>=\sum_n c_n |psi(0)> with the $c_n$ constants, then $|\psi(t)>=\exp(-iHt)|\psi(0)>
and $\exp(-iHt)|u_n>=\exp(-iE_nt)|u_n>$, so now anything like $<\psi(t)|A|\psi(t)>$ will involve objects of the form $\sum_{m,n}\exp(-it(E_m-E_n))c^*_m c_n A_{m,n}$
This bookmark processes the current page with MathJax. It has been modified from the bookmark on this page to handle $$...$$ and to handle \\[...\\] properly, to include AMS additions, and to update automatically.
The COPY TO CLIPBOARD link on pastebin.com should copy the bookmark to your clipbo...
Ok, I had mass-spring system. basic thing. But it is in a tube. When the mass is moving to the right and it reaches the end of the tube, I set the speed to zero
@Verde anyway upshot is: what i said demonstrates (if it doesn't fail for some models) that you go to some time-indep state; but there is one state for a given initial condition. this is not how you envision stat mech. this can be fixed, by using maxent aproaches, but I guess I am pushing people's patience if I start on that now :)
I am thinking now that I should have set the speed to the negative of the last speed. i.e. treat it as perfect elastic collision with the wall of the tube.
I am using NDSolve to solve one step at a time. I use the last solution as the initial conditions for the next solution
@NasserM.Abbasi I suppose it depends if you want your collision to be elastic or inelastic; if the wall is marble it'll be closer to v->-v, but if rubber, v->0 I guess
The problem is the mass is attached to a sping and not free mass. So when it hit the wall, I was not sure what to do, so I set the speed to zero for the next integration step. But now I think I should have made the speed negative, so it is more realistic I think
@acl, the mass actually does not get stuck there. Can you please try it and see if the physics makes sense to you? it is in CDF, here it is 12000.org/my_notes/mma_demos/slot_on_disk/index.htm this one sets V=0 when bob hits the wall of the disl
It does stop there for sometime, but after integration for more steps, it evantually leaves the wall back to the center of the disk. It does not get stuck there.
it depends on the spring stiffness if it gets stuck there or not. You can try test case 3 and then change the spring stiffness, then you'll see it does not get stuck for long
@NasserM.Abbasi I think that's his point, suppose you are sitting on that wall with no velocity towards the centre; the thing is rotating, pushing you to the wall with some constant apparent force. if the spring stiffness is less, you'll stay there, right?
Ok, I'll make a new version now, where when the bob hits the wallk, OR hits the center of the disk, I'll reverse the speed. Is this ok? Should be better physics
I thought of calling it 'information', but the word was overly used, so I decided to call it 'uncertainty'. [...] Von Neumann told me, 'You should call it entropy, for two reasons. In the first place your uncertainty function has been used in statistical mechanics under that name, so it already has a name. In the second place, and more important, nobody knows what entropy really is, so in a debate you will always have the advantage.' Conversation between Claude Shannon and John von Neumann regarding what name to give to the or attenuation in phone-line signals[37]
I just uploaded a new version now, where I flip the speed when it hits the wall or the center. 12000.org/my_notes/mma_demos/slot_on_disk/index.htm please see if this looks better. I think it does myself, it feels more real now that it bounces back. I can send this version to WRI before they test it
Ok, this is what I did in this version here 12000.org/my_notes/mma_demos/slot_on_disk/index.htm when the bob hits the edge of the disk, I flip the sign of the speed for the next initial conditions. When it gets to the center of the disk, I set the speed to zero. The reason is: There is a spring attached at the center of the disk. So at the center of the disk, it is not the same as the edge. I think setting it to zero there makes more sense. Please try this. Use test case (3) and hit run.
I think there is something not right in this model When I let it run for long time, it becomes unstable. Selecting test (3), set simulation speed to max, and hit run. After 1-2 minutes, the disk starts spinning much faster and things do not look right. I think I have something wrong somehere :(
I think now that flipping the speed sign when the bob hits the wall is not relastic physically since the bob is on a spring. The system is gaining kinetic energy causing the disk to spin faster now. This is not right.
Ok, now it is ok. Now it runs ok, flipping the speed at the edge. I had a bug. I was integrating one extra step, then fliping the speed after words. Now I flip the speed before. Now it is stable.
@acl I wouldn't count myself amongst some of the experts in that list. What I will say is that I have gotten a lot, LOT better in the past year and a bit since I (a) started working on my chart-drawing prototype project and (b) started participating on StackOverflow and then here.
but it is harder to get better at Mathematica compared to other languages. But if one gets better in Mathematica, they can do more with it than with other languages.
@acl, I took your advice, I added an option to select the wall type: elastic vs inelastic. The CDF is here 12000.org/my_notes/mma_demos/slot_on_disk/index.htm now when select elastic, the bob will flip speed when it hits edge. else it have speed zero there.
Ok, lets give this a try. @Mr.Wizard already showed you, how you can use Interpolate to make a function from your discrete data and since you didn't provide some test-data, I just assume we are speaking of an isosurface of a function $f(x,y,z)=c$ which is defined in some box in $\mathbb{R}^3$.
...
Consider the following code which plots a triangle.
p = {{0, 0}, {.2, 0}, {0, .2}};
{Cyan, Polygon[Dynamic[p]]} // Graphics
Then adding ( for example ) {.1, -.1} yields a non-convex polygon.
AppendTo[p, {.1, -.1}]
Question: Given a list of 2D points that are plotted as a polygon by Graphi...
