The h Bar - 2018-10-21

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12:04 AM

@amanuel2 for simple 1d systems the condition is that the net force=0.

(and net torque I suppose)

of course you can have stable or unstable equilibrium...

v.g. in the case of the pendulum at its highest point the point where position= highest and velocity=0 is actually unstable, in the sense that, under a small perturbation from the equilibrium condition, the system will not remain "close" to where it started.

Nobody recognizeable

12:53 AM

Hey guys i have a question in sr

If you measure the length of a rod in S' frame that appears to be shorter in S' frame. What happens when you measure it in S frame . Do we get more length?

And if i intend to measure the length of a rod moving with v velocity (relativistic) in S frame what happens does it get shorter?

danielunderwood

1:07 AM

The proper length is the length measured in the rod's rest frame. You'll measure a length shorter than the proper length in any frame moving relative to the rest frame

Nobody recognizeable

@danielunderwood suppose im an observer standing on a platform at rest. I wanna measure the length of train moving at relativistic speed then should i see the length contracted?

danielunderwood

1:27 AM

I believe that's the case

8 hours later…

Novalium Company

9:18 AM

Hello everybody!

A quick machine learning question. If I have a dataset with features of a house (size, design...) and the label - price, what's the simplest method I can use to predict a new house's price (with the features given)? I was thinking about supervised linear regression but what's the simplest way I can achieve that in scikit-learn python?

Anonymous

12

Q: Multivariate/Multiple Linear Regression in Scikit Learn?

I have a dataset (dataTrain.csv & dataTest.csv) in .csv file with this format: Temperature(K),Pressure(ATM),CompressibilityFactor(Z) 273.1,24.675,0.806677258 313.1,24.675,0.888394713 ...,...,... And able to build a regression model and prediction with this code: import pandas as pd from sklea...

python pandas scikit-learn sklearn-pandas

9:51 AM

morning

2 hours later…

12:18 PM

user image

bam

There we go

Nice round number

Also puts my total rep + offered bounties above @Qmechanic =P

12:45 PM

for a particle in a infinite deep potential well, It's eigenenergies are
En={n^2(pi)^2(ħ)^2}/2mL
and Ψn=√ (2/L) sin(nπx/L)

therefore the solution for time dependent schroedingers equation in terms of the infinite pot. well of thickness L will be
Ψn exp[-iEt/ħ]

im confused that for n=1

√ (2/L) sin(πx/L)exp[+(iπ^2ħ)t/2mL^2] will be the solution or not?
the exponential part is +i (not -i)

1 hour later…

2:07 PM

@ostrichguy I think that is also solution.

I didn't really check in detail, but if it's form of $\Psi(x) Exp[E/(i \hbar)t]$

you think or it is?

it is the complex conjugate tho

of the actual solution for n=1

Oh. I see that now. In that case, it's not solution. It doesn't satisfy $i \hbar \frac{\partial}{\partial t}\psi = E \psi$.

@cho

@ChoMedit how do i send a photo here?

@ostrichguy are you on a phone or a PC?

pc

2:23 PM

Do you see an Upload button by the Send button?

Eh.. Nope

user image

nope nope nope

Like so? I have an idea you don't get the Upload button until you've built up a certain amount of rep, though I forget what that level is.

I think my reputation aint enough yet

Anonymous

2:24 PM

Use imgur

@ostrichguy in that case upload the image to one of the many image sharing sites and post the link here.

Anonymous

@ostrichguy BTW you have an enviable grin. Rare for an ostrich.

Even ostriches envy me

You are mere human

Kneel

Pardon me but a little bit of humor is allowed Eh?

Anonymous

@ostrichguy They sure do ;)

Human I may be, but I eat ostrich steaks while ostriches do not eat human steaks. We shall see who has the last laugh :-)

3

2:37 PM

@ostrichguy Jesus christ what's up with your gravatar

Shit. Time to fly starts flapping feathers realizes ostriches cant fly cries

ok finally

:-)

I need help ;_;

Anonymous

@ostrichguy To fly?

nah. Need help on that problem

Anonymous

2:42 PM

@ostrichguy Maybe ask on the main site? Also, the problem is not quite legible. Use MathJax

Anonymous

2437

Q: MathJax basic tutorial and quick reference

(Deutsch: MathJax: LaTeX Basic Tutorial und Referenz) To see how any formula was written in any question or answer, including this one, right-click on the expression it and choose "Show Math As > TeX Commands". (When you do this, the '$' will not display. Make sure you add these. See the next p...

discussion faq mathjax reference

imgur.com/a/uM6P49h here I have uploaded on imgur

Anonymous

Better, hmm. I'm not exactly in the mood to read it now. Maybe someone else can help you. You'll probably have better chances on the main site though, if you can avoid making it seem like homework.

Okay... lemme try then

@JohnRennie could you please help this ostrich on the problem? Then you'll have my permission to eat me?

imgur.com/a/uM6P49h

danielunderwood

2:58 PM

@NovaliumCompany see the docs here if you want linear regression. You'd probably do a bit better with something else. My first attempt may be grad boost. That generally works pretty well for classification, but I'm not sure about the regressor

Look upon my works ye mighty and despair:

user image

Anonymous

@JohnRennie 40 pieces? :P Looks like 2 days' worth of calories

Anonymous

Do they have fillings inside? XD

I eat healthily during the week, so I like to go for it at the weekend.

They are filled with chilli beef.

drools

Anonymous

3:12 PM

@SirCumference same

danielunderwood

what are those? Are they mini pies?

user351417

@JohnRennie I remember that one. Ozymandias or something, right?

Anonymous

@Chair Yup :)

user351417

BAM!

user351417

We did that in 9th grade because reasons.

user351417

3:24 PM

Our poetry classes were actually really really strange. We named stylistic devices but never really cared about why people bothered to use them.

@Chair look upon my works ye mighty and think WTF!!!??

That's what Shelley really wrote, but his editor changed it.

user351417

@JohnRennie Language was considerably more liberal in the 18th century, I imagine.

user351417

(checking that shelley was around in the 18th century so that I don't sound like a dunce)

Anonymous

@danielunderwood We call them patties here

Anonymous

But I guess that's not the Brit term

user351417

3:28 PM

Oh well, I'm pretty sure he didn't write that one when he was 8 years old.

user351417

Guess I'm safer saying 19th century.

danielunderwood

@Blue The closest we have here are Totino's™ Pizza Rolls

it's sad

or hot pockets

@danielunderwood sausage rolls

danielunderwood

hmmm sounds delicious

A sausage roll is a British savoury pastry snack, popular in Commonwealth nations and beyond. They are sold at retail outlets and are also available from bakeries as a take-away food. A miniature version can be served as buffet or party food. == Composition == The basic composition of a sausage roll is sheets of puff pastry formed into tubes around sausage meat and glazed with egg or milk before being baked. They can be served either hot or cold. In the 19th century, they were made using shortcrust pastry instead of puff pastry. == Sales == In the UK, the bakery chain Greggs sells arou...

Anonymous

3:40 PM

@danielunderwood Do you have to heat them before eating? I never tasted those packaged pizza roll thingies

Anonymous

I suppose they wouldn't taste too fresh

danielunderwood

Yeah they're normally frozen

They aren't all that great, but we seem to be obsessed with fast/frozen food here

A lot of people I know don't seem to understand how to make regular food without premade kits/seasonings...it's kind of sad

Anonymous

@danielunderwood Making food from scratch takes a lot of time though ;) We here hardly ever have frozen food or use premade kits, but there's a price you've to pay: one person in the family has to spend more than half of their day cooking or at least you have to spend a substantial amount on hiring a cook. But well, hiring cooks is not that expensive here

danielunderwood

Yeah that certainly is true for the more involved dishes

I'm pretty sure I've spent over an hour just cutting and preparing ingredients before

I have few doubts on thermodynamics. Will anyone help me?

danielunderwood

3:50 PM

Only if you phrase your question in terms of cooking food

Anonymous

lol

@LoopBack you can ask. Thermodynamics isn't one of my strongest subjects though.

My textbook says entropy = $\dfrac{unavailable\ energy}{temperature\ of \ the \ surrounding}$ what is this unavailable energy. Can anyone explain with an example

Isn't that just another way of saying $dS = dQ/T$ ?

@JohnRennie Consider an ideal gas inside a cylinder fitted with a piston. The cylinder is has conducting walls. Few stones are kept on the piston which presses against the gas. The piston is also acted upon by atmospheric pressure. If this expansion is quasi-static then what is the unavailable energy here?

@JohnRennie I know it's another way of writing what I had written. But I want to know the actual meaning. My book just briefs everything. Nothing much is given in detail

4:08 PM

To be honest I can't remember the unavailable energy argument. I'd have to Google it to refresh my memory and it's too late in the day for me to want to do that now.

@JohnRennie I read somewhere on the internet, if a body is given heat Q1 and the body releases heat Q2. The work done by the body will be W=Q1-Q2. But not all this work is available but some is used to increase in internal energy. And that energy is the unavailable energy. But this means that unavailable energy = change in internal energy. Which i don't think is true

4:43 PM

Can anyone help me to understand what actually the term $T\Delta S$ mean?

5:31 PM

Is there a help-center article that justifies our squishiness about link-only answers? I can never find that page when I need it.

I know it's in the review queue auto-comment.

Oh, it's here. I just got impatient.

Blorp.

5

3 hours later…

8:29 PM

@JohnRennie Better not give the ostriches any ideas! They might grow accustomed to human steak

A roving flock of ostriches hunting humans for food sounds terrifying

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