The Nineteenth Byte

Cows quack

2:00 PM

@user202729 so you chose 7 arbitrarily?

user202729

@Cowsquack No, because Leaky gives 7 last digits.

ASCII-only

@user202729 hmm. so the 4 roots of 1 are just ±1 mod 2 and ±1 mod 5? (idk how to check)

user202729

@ASCII-only There are 8 roots apparently.

Also 2^(n-1)±1 mod 2^n. Somehow those doesn't work.

Leaky Nun

2 hours ago, by user202729

... the number is = 1 mod 2^n and = -1 mod 5^n.

@user202729 bingo

sorry :P

user202729

And that's why initially the brute force program report 8 roots.

@LeakyNun Takes me a while to think about CRT, nice challenge.

Cows quack

2:06 PM

@user202729 okay so we know that it is 1 mod 2^n for the first 7 digits, but how do we know it carries on to the other digits

user202729

@Cowsquack Assume n>7. If it's 1 mod 2^n and -1 mod 5^n, then it ends with that 7 digits. Therefore it satisfies the CMC.

Leaky Nun

this is my answer in python

user202729

Don't tell me that you implement gcdex ...

32 mins ago, by user202729

It's not too hard to compute it without builtin, it's just ((5^n+1)/2)^n mod 5^n. Although it would be a bit slower.

Leaky Nun

@user202729 oh?

lol

you're a genius

then 32 bytes...

New Main Posts

0

Q: Solve for 100 (game)

Challenge : given 4 numbers as inputs display one possible solution that results in 100 using operations. +-*/()^ (the ^ is for exponent) Input : You will be given 4 non-decimal positive integers as input. You can alternately take input as an array of numbers. Output : Arrange the value...

user202729

2:12 PM

I didn't mean that literally...

I mean the inverse can be computed like that.

Wait I forgot the formula...

Like this. 49 bytes.

Leaky Nun

oh, right

user202729

Without 3-arg mod, 42 bytes. Still reasonably fast.

Same trick I used with your last CMC...

Leaky Nun

what was my last CMC?

user202729

I forgot it...

chat.stackexchange.com/…

Which one @_@

Leaky Nun

lol

user202729

2:17 PM

Mar 24 at 1:17, by Leaky Nun

CMC: Solve 8x≡-3 (mod p), 0<x<p, where p is a prime greater than 5

Leaky Nun

Jan 10 at 16:09, by Leaky Nun

CMC: given n positive integer coprime with 10, output the last 100 digits of 1/n in 10-adic integers

oh

hi @DJMcMayhem

Bora Calim

i hate this. i have 21 rep. can not comment on anything. but i cant learn without commenting on stuff. this is an infinite loop

user202729

@BoraCalim (what would you like to comment on?)

Bora Calim

no i dont want undeserved rep. so dont artifically boost my rep

but

like

idk

DJMcMayhem

@LeakyNun o/

Bora Calim

2:21 PM

some questions need many clarifications

user202729

@BoraCalim ~~just vote to close as unclear instead~~

Leaky Nun

@BoraCalim everyone here went through that

user202729

(yes of course that's a joke. it needs more rep to vtc)

Bora Calim

btw, imgur is banned here so i cant see questions with images

user202729

If they're new they will be fixed (or closed) soon (by other members).

Bora Calim

2:23 PM

this one for example: codegolf.stackexchange.com/questions/120395/…

since imgur is banned, i can not see the image

user202729

Haha :D The consequence of we not having MathJax...

> the sum of the results for E(k), with each k in [1;5]

But it's already described in words...

(with new Jelly the 5-byte answer there can be 4 byte)

Anyway...

At least you have the flag. A flag to close as unclear is not very useful, and moderator flag ... well ... don't ab use it, mods are busy, ...

Probably the best way is to bring up in chat.

Muhammad Salman

@BoraCalim : You could answer some questions and get rep to comment. I got 50 rep on the first day. I suggest that you post a challenge.

user202729

Voting on this site is kinda arbitrary, just post some answers.

Especially because of HNQ effect.

Bora Calim

im not good at golfing

Muhammad Salman

Post challenges instead then

@BoraCalim : No one is good at start, we all learn, I learned mine here, still suck but better than before

user202729

2:33 PM

You don't need to be optimal, just make an attempt.

Muhammad Salman

@user202729 : what is the HNQ effect ?

user202729

(read 'serious contender')

Hot Network Questions.

Basically users who are not very familiar with PPCG visits those questions from HNQ, and just upvote "arbitrarily".

Muhammad Salman

^ didn't think PPCG challenges were posted on HNQ ?

HyperNeutrino

CMP: Should I add a ceildiv operator in Proton?

@MuhammadSalman any site's questions can be put on HNQ though some sites like SO have their HNQ rates nerfed

user202729

@HyperNeutrino Yes.

@BoraCalim (useful resources: Try it online!)

Muhammad Salman

2:36 PM

@HyperNeutrino : Oh, Okay

user202729

(actually, mostly for formatting posts.)

Muhammad Salman

^ The most useful resource.

HyperNeutrino

it'll be a bit annoying because then I need to custom-define it instead of using the Python semi-wrapper, but I need to implement my custom definition of and and or anyway

DJMcMayhem

@MuhammadSalman Every site other than Math Overflow is posted on HNQ

HyperNeutrino

should I implement list-by-number division (as in split into parts)

@DJMcMayhem wait why does MO not get HNQ o_O

Muhammad Salman

2:38 PM

@DJMcMayhem : what's wrong with Math overflow

Poor math overflow :(

DJMcMayhem

They requested to not have their questions on HNQ iirc

user202729

@HyperNeutrino Because they chose not to.

HyperNeutrino

oh ok

user202729

Actually, some people (Peter Taylor for example, IIRC) think that HNQ is bad for the site. Reason above.

Muhammad Salman

Can't you guys request that too. (wonder why they did)

HyperNeutrino

2:39 PM

actually no list-by-number div is a bad idea

DJMcMayhem

@MuhammadSalman We could. Personally, I don't think we should

Muhammad Salman

Aww man, my challenge was closed.

user202729

And even if we do request it, it would probably take ages before SE responds.

Muhammad Salman

^ ? why ? they can't be that slow

user202729

16

Q: Can we have MathJax back (part II)?

More than a month ago, we've reached a consensus: We want MathJax back. The reasons why it was turned off in 2015 no longer seem to apply, and details about why MathJax is needed on this site are detailed in the linked post. After a while, I asked a Community Manager about what we shall do next, ...

feature-request latex

DJMcMayhem

2:41 PM

Speaking of which, we still need to get mathjax enabled. Ninja'd

Muhammad Salman

what is mathjax ?

DJMcMayhem

52

Q: Can we raise the privilege levels?

PPCG has graduated. Some features for graduated sites come immediately after graduating. However, other features are held off for an indefinite amount of time: The site gets a custom theme, and Privilege levels, which are initially lowered to help growing beta sites grow, are raised to match th...

discussion graduation privileges

user202729

Jun 1 at 2:58, by user202729

https://codegolf.meta.stackexchange.com/revisions/16447/2

That one was edited by Shog9.

New Meta Posts

0

Q: Creating challenges from homework.

Recently I've been posting a lot of challenges on the site. This is because I am in a class where the homework are programming challenges (Algorithm Class). Is that OK? or should I stop posting them? I ask because I know this is not site for homework (Yes, the answers helps me to create better ...

discussion

DJMcMayhem

@MuhammadSalman Comments will still be at 50. It's just moderation related privileges that would be adjusted

Muhammad Salman

2:47 PM

@DJMcMayhem : Yeah, I like the privilages I have, and I think I would prefer if they stay with me.

DJMcMayhem

Oh whoops, I guess I confused you with Bora lol

Bora Calim

yes

user202729

@DJMcMayhem ???

Muhammad Salman

why do you guys want to raise it anyway ?

Bora Calim

finally

user202729

2:52 PM

@MuhammadSalman (read the linked question please)

DJMcMayhem

@MuhammadSalman long story short, the current levels are for beta sites, and we are not a beta site

Muhammad Salman

^ Okay, done and now voted as well. I am considering down voting the question and nominating to close it as well :) JK

We can say we are the only non-beta site that still has these. that makes this site unique

^ probably a lame excuse

user202729

@MuhammadSalman Downvote if you want, but don't abuse close votes.

People abusing their close votes are the exact reason why the mods want to raise the privilege levels.

@MuhammadSalman Not really...

dzaima

@MuhammadSalman we aren't the only site that's graduated but doesn't have a design & privilege levels (e.g. anime)

Muhammad Salman

^ I was just joking, I barely down-vote anything and the comment was exactly meant for that

@dzaima : Thanks for informing me :(

Bora Calim

3:01 PM

guys any of you know alternatives to brainfuck-style loops in a language which does not have numeric literals?

user202729

@BoraCalim How is numeric literal related to loops?

Muhammad Salman

^ I think he meant doesn't support numbers directly ?

Bora Calim

yes

the language does not support numbers

Cows quack

@user202729 I meant to ask how do we know that it doesn't change from, say, -1 mod 5^n for some of the digits to 1 mod 5^n to the other (sorry if stupid question)

Bora Calim

and i tried to implement a brainfuck style loop which would execute commands until the popped value from the stack is zero

but it did not work properly

and i got mad and deleted the loop code

user202729

3:04 PM

@BoraCalim idownvotedbecau.se/itsnotworking

Muhammad Salman

^ LOL (the site name)

user202729

@Cowsquack I don't understand the question. As long as it ends with <those 7 digits> and it's a square root of 1 it should be fine, right?

Bora Calim

@user202729 i did not ask how to fix it

user202729

@BoraCalim Then?

Bora Calim

i asked for an alternative to brainfuck-style loops

thats not fixing

user202729

3:06 PM

There are goto ...

Bora Calim

we have to say goto x

user202729

(For an esolang it should be fine)

Bora Calim

and only values from a stack is reachable

Cows quack

@user202729 why isn't there a root to 1 that ends in those 7 digits (where the numbers follow -1 mod 5^n), but also from the eighth digit it follows 1 mod 5^n instead

Bora Calim

and those values can only be manipulated with + and - like in brainfuck

Muhammad Salman

3:07 PM

Then why don't you just implement the BF loop ?

Bora Calim

because i cant

it did not work

and i cant program properly

user202729

The CMC says "the root". Assume Leaky is correct, there is only one root.

Cows quack

(just so I'm clear, I'm not talking about the cmc anymore, I'm just talking about 10-adic roots of 1)

user202729

Ok...

Cows quack

"Assume Leaky is correct" is there a proof for why there is only 1 such root that ends in those digits?

Muhammad Salman

3:09 PM

O_o ? goto statements as user202729 suggested ?

Bora Calim

there are no numbers so goto can not work

you can push 0 to stack

and then the only thing you can do is

Pavel

CMP: Have you actually migrated your GitHub projects to GitLab?

Bora Calim

increment and decrement the top of the stack

and sometimes pop it or print it.

user202729

@LeakyNun chat.stackexchange.com/transcript/message/44987935#44987935

redirect the question

Leaky Nun

lol

there are 4 roots of 1 in the 10-adic world

every 10-adic number correspond uniquely to a pair of 2-adic and 5-adic number

this correspondence respects addition and multiplication

this is just Chinese Remainder Theorem

Muhammad Salman

3:13 PM

@BoraCalim : why not post a question on SO instead ?

Leaky Nun

@Cowsquack do you follow?

Cows quack

@LeakyNun how so? could you give an example?

Bora Calim

@MuhammadSalman because my code is like 100 lines long and people on SO will not like my asking style

and most lines are connected to each other

user202729

@BoraCalim Then MCVE-ify it...

Bora Calim

thats impossible

Muhammad Salman

3:15 PM

^ why ?

user202729

Then....

If it's impossible to reduce it further, then it's already minimal.

By its definition.

Leaky Nun

@Cowsquack for every m, integers modulo 10^m correspond uniquely to a pair of (integer modulo 2^m, integer modulo 5^m)

Bora Calim

no like i should not delete the other 80 lines because i can not display what i want to display to SO without them

Muhammad Salman

Go to SO, ask the same question and paste a link to GitHub instead of posting the whole code (I assume that the code is commented)

user202729

@BoraCalim codeblog.jonskeet.uk/2010/08/29/writing-the-perfect-question

@MuhammadSalman -1. Questions should be self-contained. VTC as "lacks a minimal example".

Leaky Nun

3:17 PM

@Cowsquack 11(ten-adic) corresponds to (1011(two-adic), 21(five-adic))

1011 is written in base 2

Muhammad Salman

@user202729 : Did I get a -1 vote. Hay I'm not exactly the master of writing questions ?

Leaky Nun

21 is written in base 5

@Cowsquack consider the number ...123123 (ten-adic), you can view it as the limit of the sequence (3, 23, 123, 3123, 23123, ...)

you can convert each number in the sequence to binary, and I can guarantee that the new sequence converges

and you can do the same for base 5

Cows quack

ok

Leaky Nun

pyth.herokuapp.com/…

(first input = number of terms; second input = base)

the sequence in base 2 reads:

11
10111
1111011
110000110011
101101001010011
11110000011110011
1011111010011110110011
1011000001101010010110011
111010101101011010110110011
10111010001001110001001110110011
10101100010001111101101101110110011
1110010101010101101011100001110110011
101101011100101000101001001111001110110011

base 5:

3
43
443
44443
1214443
12414443
1244414443
21404414443
223004414443
22344004414443
334324004414443
4004124004414443
402132124004414443

@Cowsquack if you know some abstract algebra, the p-adic integers form a ring

for prime p, the ring of p-adic integers is an integral domain

Mr. Xcoder

Wheeeee a Pyth program being used in chat :)

Leaky Nun

3:24 PM

which is to say, that if ab=0, then a=0 or b=0

(the same is not true in the 10-adic land since 10 is not prime)

Cows quack

(I don't know rings)

Leaky Nun

ignore that then

in the p-adic land, where p is prime, ab=0 implies a=0 or b=0

(to see how this fails for 10-adic, take that square root of 1, call it x, then x^2=1, i.e. (x-1)(x+1) = 0, but clearly neither x-1 nor x+1 is 0

54 secs ago, by Leaky Nun

in the p-adic land, where p is prime, ab=0 implies a=0 or b=0

should I prove this?

user202729

@LeakyNun No.

Cows quack

I'm fine with this, please go on

Leaky Nun

13 mins ago, by Leaky Nun

every 10-adic number correspond uniquely to a pair of 2-adic and 5-adic number

13 mins ago, by Leaky Nun

this correspondence respects addition and multiplication

in particular, every integer n is sent to (n,n)

[integer as in, really an integer]

user202729

3:27 PM

(they're just finite p-adic numbers without a fractional part)

Cows quack

@LeakyNun what is (n,n)?

Leaky Nun

the pair of n and n

user202729

@Cowsquack A tuple of 2 elements, each one is n.

Cows quack

okay

Leaky Nun

in the p-adic land, if x^2=1, then x^2-1=0, so (x-1)(x+1)=0, so x-1=0 or x+1=0, so x=1 or x=-1

Cows quack

3:29 PM

(gtg, I will be back later)

Leaky Nun

this fails in the 10-adic land because (x-1)(x+1)=0 does not imply x-1=0 or x+1=0

so there are 2 square roots of 1 in the 2-adic land and the 5-adic land respectively

which gives 4 square roots of 1 in the 10-adic land by the correspondence

Transcript for