The h Bar

Cows

00:00

I will be watching in an attempt to learn stuff

0celo7

what do you need

Rumplestillskin

I am not sure about this minus sign in the following identity: $\frac{d}{d\tau} g^{\mu\rho} = -g^{\mu\alpha}g^{\rho \beta} \frac{d}{d\tau} g_{\alpha \beta}$... The indices are fine I just don't get the minus sign

0celo7

yeah you get a minus sign

it comes from differentiating $g_{\mu\nu}g^{\nu\sigma}=\delta_\mu^\sigma$

Cows

hmm that was fast lol

Rumplestillskin

Hmmm I still am not really sure I get it. @0celo7

Cows

00:05

@0celo7 can we discuss the equation he just mentioned?

Are you refering to the -1 in the matrix?

0celo7

@Cows what?

@Rumplestillskin write down the derivative of what I wrote

note that the RHS is constant

(write it here)

Cows

before I proceed let me declare complete ignorance

in the subject

Looking at this with no clue, I would imagine the - sign is from differentiating

I was just saying g is a matrix

a trivial and useless fact lol

anyways returning to watching mode

0celo7

the minus sign is there for the same reason there's a minus sign in the derivative of $1/f(x)$

Cows

yes

wait?

I need some context

what is $g^{\mu \rho}$ in this case?

0celo7

inverse metric

Cows

00:11

$\tau$ is some parameter

ahh dacord . .

Phase

@ACuriousMind WE ARE GOING TO PLAY CS:GO ADD ME

Cows

so yes it makes sense

to put the minus

where is this identity from?

Rumplestillskin

Ah okay so it comes from differentiating the inverse metric?

Cows

Can i see the form of the matrix (metric) anyone . ..

Rumplestillskin

@Cows there is no particular form. This is just a general identity

Cows

00:13

@Rumplestillskin do you have a picture of the metric in matrix form?

@Rumplestillskin sorry I meant form not in the math sense, I just wanted to see the metric written explicitely just for kicks

Rumplestillskin

@Cows I am doing this generally for a test particle moving along a geodesic. The metric is not prescribed.

Cows

oh i see

So i take it you want to compute some Christoffel symbols?

btw, i know nothing. . i am just attempting to learn

Rumplestillskin

@Cows No not at all. If you look at this question you will see what I am doing

https://physics.stackexchange.com/questions/365490/integration-of-equations-of-motion-in-gr/366361#366361

Cows

I see

let me look at your equation above a again to recalibrate my next outgoing comment

Rumplestillskin

Ahhhhhh Of course @0celo7!!!! My god I have no idea how I didn't get that. Im a bit embarassed haha! Thanks mate! @Cows If you like I can talk you through it

Cows

00:19

that would be great

Rumplestillskin

Well I will explain it as @0celo7 has. Do you know how to calculate the derivative of $f(x)^{-1}$... It is give by the chain rule.

So it will look something like $-f(x)^{-2} \frac{d}{dx}f(x)$

Cows

yes

Bernardo Meurer

@dmckee Why did I just get a timeout notification banner?

Cows

so same chain rule from calculus

Bernardo Meurer

Swear to God I saw it

Rumplestillskin

00:23

So if we look at \frac{d}{d\tau} g^{\mu\rho}. This is the same as the inverse of g_{\mu\rho}. Then the derivative will follow the same way as above for $f(x)^{-1}$.

Cows

@Rumplestillskin although I usually write out the d operator explicitely

ACuriousMind

@BernardoMeurer Likely because your connection is bad, nothing on the SE side :P

Rumplestillskin

The d operator??

Bernardo Meurer

@ACuriousMind So you banned me for no good reason, is that what you're saying?

Cows

@Rumplestillskin d something dx sorry if my math diction is off

Bernardo Meurer

00:24

Lol, I just nuked a VM because the internet wasn't working on it

turns out it was my internet :(

ACuriousMind

aha.

Cows

@Rumplestillskin I see now

@Rumplestillskin I love GR, I want to be awesome at it someday.

Rumplestillskin

haha I like it a lot too! In fact I study it almost every day but I still mess things up quite frequently!! I want to try and teach it in the next 2-3 years. I think this is definitely the best way to sink your teeth in to something. Are you familiar with Dalarsson and Dalarssons book on relativity? Excellent if you havent came across it before

Cows

@Rumplestillskin believe it or not I own that book lol

you mean Tensors, Relativity and cosmology right?

They show most of the calculations in detail

Rumplestillskin

I think it's one of the best books for learning about tensors. And also the book "Tensor calculus" by Barry Spain.

Yep that's the one @Cows

Cows

00:31

hmm i don't have the other text, let me google it

nice

@Rumplestillskin You know ... you can test drive teaching GR on me. I will be a happy guinea pig. We can set up a room on the site and time for a quick dry run. hehe

Rumplestillskin

Hahaha! Maybe soon @Cows at the minute Im trying to finish a paper for rejection :)

Cows

@Rumplestillskin ahhha lol, I'm sure your paper will make it :D

Rumplestillskin

Fingers crossed :)

heather

00:50

apparently scientific papers in europe will now be free?

if so: !?!? =D ::mild jealousy as an american::

Phase

@ACuriousMind oi where you at

0celo7

Phase called you a heck

Mithrandir24601

@heather This would be fantastic... Assuming 'Europe' means 'Europe' and not just 'EU'...

heather

it might be the EU, I don't know.

the article wasn't very clear (and I kinda skimmed it).

Rumplestillskin

01:47

@0celo7 could you hep me with one more bad boy?

vzn

@heather :) big news, thx for sharing. viva la open access/ science. fyi the actual link ponderwall.com/index.php/2016/07/14/…

0celo7

@Rumplestillskin maybe

Bernardo Meurer

02:39

0celo7

@Rumplestillskin yeah

Bernardo Meurer

@dmckee @JohnRennie and now, proudly, @ACuriousMind, thought y'all would enjoy that :P

0celo7

@BernardoMeurer can you play left 4 dead 2 on your laptop?

Bernardo Meurer

Maybe

Cows

04:50

Going hardcore on some code

good night

05:04

@Cows woah relax

enumaris

stupid file transfer takes forever

0celo7

use a thumb drive

enumaris

slowed down from 110mb/s to 7.8mb/s originally was supposed to take 2 hours, it's been 6 LOL

It's an external, connected via USB3

0celo7

huh

break it then

it's worthless

enumaris

I dunno why it's slowing down exponentially lol

tbf I am transfering 300gb of data, but it still shouldn't take this long

I hope when I have to transfer 1.5tb tomorrow it'll be a lot faster lol

Bernardo Meurer

05:15

@enumaris What on earth are you doing

enumaris

the 1.5tb of data is only in 127 files tho, unlike this batch of 300gb which is in 1 million+ files

training neural networks lol

Bernardo Meurer

Are you using rsync ?

if so the z option will enable compression, which helps a lot with transfers over networks

Depending on the data

enumaris

I'm using the graphical interface

u know

like click drag the file over

0celo7

it's adult movies

enumaris

let's see what the program is called

0celo7

05:18

you scoundrel

enumaris

nautilus

the 1.5tb of data is actually just a bunch of numpy arrays lol

saved in npz files

128 .npz files each containing 3 arrays

I want to convert all 128 .npz files into one .hdf5 file

but I don't have enough storage to do that so I gotta move some off my harddrive first

Bernardo Meurer

@enumaris Dawg

Of course it will take forever

nautilus is dumb af

enumaris

lol

Bernardo Meurer

use rsync's CLI

enumaris

is that the program that comes with my HD or is that from ubuntu

Bernardo Meurer

05:24

rsync -avz SOURCE DEST

Ubuntu

enumaris

I see

Bernardo Meurer

rsync -az --checksum --delete --info=progress2 /mnt/media/* ./backup

e.g. usage

enumaris

what's the -avz flag

copy/cut?

Bernardo Meurer

-a is archive

-v is verboze

-z is compress

enumaris

do I have to zip it

Bernardo Meurer

05:25

No

Rsync does it

enumaris

o

Bernardo Meurer

You need to do nothing

Rsync handles it all

enumaris

if I wanna move multiple files, I gotta put them all in a folder first tho?

Bernardo Meurer

rsync -avz --info=progress2 /SRC/ /DEST/

@enumaris No, you can use find in a subshell

enumaris

the info flag prints out a status update?

Bernardo Meurer

05:26

I suppose

Or just glob'em with wildcards

enumaris

uh...

Bernardo Meurer

rsync -avz /SRC/*.txt /DEST/

for e.g.

enumaris

can I just put them all in a folder and then use the filepath to the folder

Bernardo Meurer

Yes

That's what I do, because I don't like to rely on pattern matching

enumaris

I'll do that heh

Bernardo Meurer

05:28

You should take the time to learn UNIX, it makes life much easier :)

Or just ask me when you need help :P

enumaris

I only know as much as is needed to complete any given task that I need to do

and then the information is promptly forgot

mostly I just know ls, cd

lol

Bernardo Meurer

Good lord

Well, now you know rsync

OH

enumaris

I used that to download the data

and then I promptly forgot about it

Bernardo Meurer

Watch out

enumaris

about what

Bernardo Meurer

05:29

if you pass --delete to rsync it will delete everything in /DEST/ not in /SRC/

enumaris

I'll just never pass --delete then lol

I'll do deletion manually

Bernardo Meurer

That's a waste of your time a lot of the time

e.g. a backup

enumaris

40 min left for nautilus to complete its job

Bernardo Meurer

You should really try and learn how to use these tools, they will make you more efficient

enumaris

assuming it doesn't slow significantly from 7.7mb/s

Bernardo Meurer

05:32

I really don't trust nautilus...

It just uses cp

enumaris

I already spent a day installing cuda on my system so my training is 100x more efficient than before

GPU acceleration is so boss

Bernardo Meurer

Why did it take you a day to install cuda? O.o

enumaris

I installed cudann7 and toolkit 9

discovered tensorflow wouldn't work with them

so I downgraded to cudann6 and toolkit 8

Bernardo Meurer

Just stop using Ubuntu

It's such a piece of shit

Nothing works on that crap distro

enumaris

then discovered there are builds of tensorflow that uses 7 and 9...

lol

Bernardo Meurer

05:33

I'm always amazed by how they manage to make a distro where literally nothing fucking works

enumaris

I didn't bother to reupgrade to 7 and 9 tho

Bernardo Meurer

Use Antergos, Manjaro, OpenSUSE (Tumbleweed), Debian, Arch

But not Ubuntu

enumaris

hmm

I've bricked my computer multiple times reinstalling OS tho

so I'm loathe to do that...

usually I screw up the BIOS

Bernardo Meurer

You mean the UEFI?

Or actually BIOS

enumaris

I think the BIOS

Bernardo Meurer

05:35

Are you dual-booting?

enumaris

the booter

I did that on my previous computer yeah

dual booting ubuntu and windows

Bernardo Meurer

ls /sys/firmware/efi/efivars

enumaris

and it bricked - can only start up with the USB drive in there lol

Bernardo Meurer

See what this outputs

enumaris

a lot of stuff

Bernardo Meurer

05:37

It's UEFI :)

enumaris

this is not the computer I bricked though

I bricked 2 previous computers doing dual booting

Bernardo Meurer

Yeah, dual-booting with EFI is a bit more complicated than with good old BIOS

enumaris

LOL

Bernardo Meurer

Dude what on earth are you doing

It's not that hard

Also you don't "brick" them

enumaris

technology hates me

Bernardo Meurer

05:37

You can fix it quite easily

enumaris

temporarily bricked

but the panic sets in

Bernardo Meurer

Panic?

enumaris

cus nothing appears on screen when u power on

Bernardo Meurer

Wat

Ah

Your panic, not kernel panic

enumaris

lol yeah

Bernardo Meurer

05:40

Anyway

If you ever run into trouble with something like that

email me

enumaris

alright XD

Bernardo Meurer

I usually respond quickly, and if I'm near a computer I can SSH and fix it in a jiffy

enumaris

I see

cool, thx :D

I wonder why the data transfer got progressively slower tho

little by little

seems weird

Bernardo Meurer

Because nautilus is a piece of shit that doesn't use the right tools :)

DanielSank

@BernardoMeurer groan

Can't you ever stop complaining about Ubuntu?

Bernardo Meurer

05:44

@DanielSank Heyo

No

enumaris

lol

Bernardo Meurer

It sucks

DanielSank

@BernardoMeurer Ok!

Bernardo Meurer

You know it does

enumaris

are other linux distros similar in use...or are they like...command line interfaces...

I'm not too good if all I get is a command line...

Bernardo Meurer

05:45

All of the ones I listed can have a nice friendly GUI

enumaris

I see

Debian is the only one I heard of lol

Bernardo Meurer

I recommend Antergos with Gnome as a GUI (DE), or Manjaro

DanielSank

@enumaris Dude, there are a bazillion GUI linux distributions.

Bernardo Meurer

^

DanielSank

Linux distribution

A Linux distribution (often abbreviated as distro) is an operating system made from a software collection, which is based upon the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one of the Linux distributions, which are available for a wide variety of systems ranging from embedded devices (for example, OpenWrt) and personal computers (for example, Linux Mint) to powerful supercomputers (for example, Rocks Cluster Distribution). A typical Linux distribution comprises a Linux kernel, GNU tools and libraries, additional software...

enumaris

05:46

uh...

DanielSank

The first figure in that article is pretty amazing

@BERNARDO

I NEED A BASH SCRIPT TO RECURSIVELY DELETE ALL DIRECTORIES CALLED build/ UNDER MY CURRENT DIRECTORY.

Bernardo Meurer

manjaro.org/community-editions

DanielSank

CAN YOU DO IT

Bernardo Meurer

@enumaris I recommend cinnamon as a DE :)

Yeah

I can

One second

DanielSank

@BernardoMeurer Cinnamon is ok, but it's not as pretty as Unity. Unfortunately, Unity is being discontinued.

enumaris

05:48

what's a DE

DanielSank

Desktop Environment.

enumaris

oh

DanielSank

Linux is an operating system, but you can use a huge variety of desktops to use it.

enumaris

I feel like...I already spent a lot of time installing a lot of stuff on my system...I dunno if I wanna redo everything -.-

DanielSank

That's one of the cool things about Linux being open software: you aren't stuck with whatever one company happens to sell you.

@enumaris Then don't :-)

enumaris

05:49

are there ubuntu skins that look cooler than the default one

are DEs like skins

lol

Bernardo Meurer

Oh fuck daniel

I just recursively created build folders all over my system

enumaris

LOL

gotta be careful with bash script...

Bernardo Meurer

I'm usually the master of bash

But I misplaced a cd

I guess I'll use the script to fix it now, lol

K

Got a test setup

enumaris

only 40k files left to transfer...

0celo7

that's a lot of adult films

enumaris

05:54

-.-

Bernardo Meurer

@DanielSank Got em :)

for i in $(find . -type d)
do
    if [ "$(basename "$i")" == "build" ]
    then
        rm -rf "$i"
    fi
done

@DanielSank I rule

enumaris

so that's what bash syntax looks like

lol

Bernardo Meurer

Yep

enumaris

quick question, to start up ssh, I would type "sudo systemctl start ssh" right

I guess I can just try it...

John Rennie

Which flavour of Linux?

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