The Nineteenth Byte

Anonymous

3:00 PM

It's matrices all the way down

-2

Statement Given distinct integers, output them in order such that the jth output is larger than the (j/2)th output if and only if j is odd, for j from 2 to the number of given integers. This is a code golf. Output shall be in decimal, with some separator. 2 to 99 non-negative distinct integers ...

Mr. Xcoder

@Adám Yeah excuse me, I was just confused

Dennis

@Mr.Xcoder I'm not sure I understand. Is this what you mean by 4D?

Erik the Outgolfer

@user202729 true

totallyhuman

3:21 PM

tio's down?

user202729

No.

Adám

@totallyhuman Nope.

totallyhuman

D: did my school block tio

Dennis

One of the servers is currently being rebooted by DO. Didn't take it offline in time.

totallyhuman

oh thank goodness no

oh i just realized matlab's not on tio ;-;

user202729

3:24 PM

... because it is not free?

totallyhuman

yeah

but i think a cop's in matlab... but matlab's not legal on tplq

Dennis

Unless they offer me a free license, that's not going to change.

totallyhuman

0

A: The Programming Language Quiz, Mark II - Cops

???, 43 bytes a:=[];for(n:=1;n<101;n:=n+1)a:=append(a,n); I hope this isn't too easy

user202729

Tell them that languages must be free.

New Sandboxed Posts

0

A: Sandbox for Proposed Challenges

Formerly Composite Numbers code-golf sequence primes Construct a sequence of positive integers a(n) as follows: Each new successive term must be the smallest number that 1) is itself composite, 2) is larger than the previous term, and 3) when you add the new term to each of the previous terms p...

user202729

3:26 PM

(even languages which can only be run on Windows may be considered not free, there is a AHK submission)

Adám

@Dennis May it will sway them if they are made aware that Dyalog and Wolfram have granted you permission to put APL and Mathematica on TIO for free?

user202729

Some people just think that Windows is free. (is it? I think the non-registered version only has the annoying watermark)

@Adám If they somehow get to know about it.

19 hours ago, by Pavel

@PhiNotPi Wolfram Research reached out to Dennis. To date, we're not sure how Wolfram Research found out about TIO.

moonheart08

I honestly dislike the idea of paying for a programming language. For Mathematica or MATLAB, it's understandable, because they're DSLs made for a specific task. APL seems a little out of place there.

Adám

@user202729 Right, and Dyalog also reached out to Dennis.

user202729

DSL? Domain specific language?

moonheart08

3:29 PM

Yea

Mathematica and MATLAB are DSLs intended for mathematics and computational research (or whatever the term is)

Adám

@moonheart08 And APL?

moonheart08

APL is more of a general purpose language in my opinion.

totallyhuman

or maybe it's not matlab

confusing docs o0

Adám

@moonheart08 I'm happy to hear.

@totallyhuman Maybe what isn't MATLAB?

totallyhuman

0

A: The Programming Language Quiz, Mark II - Cops

???, 43 bytes a:=[];for(n:=1;n<101;n:=n+1)a:=append(a,n); I hope this isn't too easy

user202729

3:32 PM

The submission.

totallyhuman

might be mupad

user202729

I tried computer brute force all programs with length < 5 and consists of only characters:

('ṡ', '€', 'Z', 'Ẏ', '⁸', '⁹', '⁹Ƥ', '⁺'). No solution.

moonheart08

iczero's submission. I think he did a good job (I know what it is, but i know because he told me, so i'm entitled not to tell :P)

user202729

Apart from Dennis' answer it also found ṡ€Z⁹Ƥ as a 4-element.

AdmBorkBork

And now it's been deleted. I wonder if the OP is going to sandbox it, or just abandon it.

user202729

3:42 PM

(it = NMP)

AdmBorkBork

Yes, sorry, I could've been more clear on that.

VtC my statement as unclear.

user202729

After 506 seconds I get all the possible results of 6 or 7 bytes: (5 of the

('ṡ', '€', 'Z', 'Ẏ', '⁸', '⁹', '⁹Ƥ', '⁺')):

code: ṡ€Zṡ€
code: ṡ€Z⁹⁹Ƥ
code: ṡ€Z⁹ƤZ
code: ṡ€Z⁹Ƥ⁹Ƥ
code: ṡ€⁹Z⁹Ƥ
code: ZZ⁹Ƥṡ€
code: Z⁹⁹Ƥ⁺€
code: Z⁹Ƥ€Z⁹Ƥ
code: Z⁹ƤZ⁹Ƥ€
code: Z⁹Ƥ⁺€Z
code: Z⁹Ƥ⁺⁹Ƥ€
code: Z⁺⁹Ƥṡ€
code: Ẏ⁹Ƥ€Z⁹Ƥ
code: ⁸Z⁹Ƥ⁺€
code: ⁸⁹Ƥ€Z⁹Ƥ
code: ⁹⁹Ƥ€Z⁹Ƥ
code: ⁺ṡ€Z⁹Ƥ
code: ⁺Z⁹Ƥ⁺€

(which passes one, not all, test case)

Some of them looks very weird, I wonder why they don't error out.

CMC: Given Mathematica matrix format of second argument of Flatten output a string of Jelly code of Z, Ẏ, € with the same behavior.

betseg

can i ask a geometry question here, we've been discussing it with some classmates for almost half an hour

AdmBorkBork

Sure, I like geometry.

I'm sure I'm not alone.

betseg

1 sec

i.stack.imgur.com/GVexH.png how many chords that pass through P have an integer length

Anonymous

3:50 PM

@betseg The radius is 5

betseg

@Mego :O

AdmBorkBork

Well, the longest chord is straight through the diameter with length 10, right?

betseg

probably

AdmBorkBork

No, it is, you can't get a longer chord than through the center.

betseg

ye

AdmBorkBork

3:55 PM

The shortest chord would be perpendicular to your line, passing through P.

Is that an integer length chord?

betseg

i think it's 8 units

3-4-5 triangle

Anonymous

@betseg The chord's length must be in [8, 10]. 10 is the diameter which passes through P (the extension of the radius given in the image), so that's one. Using trigonometry, we can see that the shortest chord has length 8.

AdmBorkBork

Right

Anonymous

So the question is, is there a chord of length 9 that passes through P? Since sin and cos are continuous, the answer must be yes. So, there are exactly 3 chords with integer length that pass through P.

AdmBorkBork

Four chords

betseg

3:59 PM

2 9s

Anonymous

Oh right, I was counting distinct lengths :P

betseg

ty

AdmBorkBork

The hidden thing behind Mego's statement is the Intermediate Value Theorem

Anonymous

@AdmBorkBork Yep. I handwaved over it because it's so trivial and intuitive :P

AdmBorkBork

lol

betseg

4:02 PM

I didn't know it even had a name

Anonymous

It comes up a lot in calculus

Anonymous

And it's also proven using calculus

Poke

I love the intermediate value theorem

It helped while proving that my brother was 5 years old at some point in his life

Anonymous

I love that it's so intuitive, but it still requires calculus (in the sense that an epsilon-delta proof is calculus) to formally prove :P

Poke

gotta say though... nothing in math comes close to the pigeonhole principle

that bad boy is a work of art

PhiNotPi

4:08 PM

Just posted my 4th challenge in < 48 hours. Get hype!

Poke

One minute you're having some nice discussions about discrete math

The next you're talking about birds

Pavel

Should probably do something with best-of

Now that voting has closed, and all

PhiNotPi

#PhiPhlood2018 (pronounced "flood" not "flued")

Anonymous

@Poke The fact that it has such a silly name makes me happy

AdmBorkBork

@PhiNotPi Killing your progress toward Socratic

Poke

4:11 PM

@Mego I loved listening to my professor describe it in school

it made me laugh

PhiNotPi

@AdmBorkBork Yeah maybe I should space them out more.

Poke

"Suppose we have n pigeonholes and and n+1 pigeons"

AdmBorkBork

@PhiNotPi Especially if you're also going to beat DJ like I am ;-)

Pavel

@Poke If you talk with a Russian mathematician, he'll call it Dirichlet's Principle, as if something so simple needs to be named after someone.

Anonymous

There are hundreds of better options for formal-sounding names for the PP (including the Schubfach Principle, the Tiroir Principle, Dirichlet's Inclusion Principle), but yet everyone still calls it the Pigeonhole Principle

Pavel

4:13 PM

Man, I spelled Dirichlet way wrong

Anonymous

Yep :P

Poke

i think discrete math and linear algebra were my favorite math classes in college

they were a ton of work, though

haha

Anonymous

Also Dirichlet's Principle is something quite different: en.wikipedia.org/wiki/Dirichlet%27s_principle

Pavel

Can someone ELI5 the point of linear algebra? Whenever I think of "linear" I think of y=mx+b but something tells me it's more complicated than that.

J. Sallé

@Poke I felt like dying the first week of college with Discrete Maths

PhiNotPi

4:16 PM

@Pavel linear algebra = matrices

AdmBorkBork

@Pavel If you want to do anything in higher mathematics, you need Linear.

J. Sallé

but then again, my professor was Italian, didn't speak a word of Portuguese and assumed everyone in the class (of freshmen!) had 4 PhDs like him.

Anonymous

@Pavel Linear algebra is the branch of math concerning linear equations and systems of linear equations. A linear equation has the form a_1 * x_1 + ... + a_n * x_n = b

Anonymous

(a linear combination of unknowns)

Pavel

There we go, I knew it had to be harder than Algebra I :P

Riker

4:18 PM

that's more than 5 year old english

Anonymous

y = m*x + b is a linear function of one variable. It's still technically linear algebra, but it's the second-simplest example of a linear equation.

Riker

"linear algebra makes you know many things, if you only know one thing"

@Mego third simplest I think

y = x, but y = c is techinically one too isn't it

Pavel

Although we never covered matrices in Algebra I. We were supposed to, but, "You'll cover this in Algebra II, so we're skipping it." In Algebra II, "You covered this last year, so we're skipping it."

So I still don't know how matrices work properly.

mudkip201

lol

Anonymous

@Riker y = x is still a univariate linear function. The only simpler kind is a constant function.

Riker

4:19 PM

it's not like they cover much about matrices tho

moonheart08

lol

Riker

@Mego ah ok

@Pavel tl;dr; 2d rect arrays in pretty much every way

Pavel

I haven't needed them since, so I'm just going to assume I would have forgotten all about them by the time I got into linear algebra anyway.

New Main Posts

3

Q: Verify Cyclic Difference Sets

A cyclic difference set is a set of positive integers with a unique property: Let n be the largest integer in the set. Let r be any integer (not necessarily in the set) greater than 0 but less than or equal to n/2. Let k be the number of solutions to (b - a) % n = r where a and b are any member...

code-golf number number-theory

Pavel

@Riker *2D rectangular arrays

Riker

4:20 PM

ftfy

Anonymous

@Pavel Matrices are 2D rectangular collections of values. They're mostly used to represent systems of linear equations, and by Adám to golf his APL code.

Anonymous

You can also generalize a lot of algebra and calculus to matrices, but it's usually not worth the effort.

Pavel

I can't even generalize multiplaction to matrices

Anonymous

For example, a lot of functions that are injective over reals are not injective when extended to matrices

Anonymous

@Pavel Let A be a n x m matrix, and B be a m x p matrix. AxB is the n x p matrix where each value is equal to the product of the corresponding row in A and the corresponding column in B (which itself is equal to the dot product of r and c_T, where r is the row from A, c is the column from B, and c_T denotes the transpose of c).

Pavel

4:27 PM

This is generally explained with an illustration isn't it

Anonymous

Yes

Pavel

I'll just look it up

Anonymous

[[a, b], [c, d]] x [[w, x], [y, z]] = [[a*w + b*y, a*x + b*z], [c*w + d*y, c*x + c*z]]

Anonymous

Multiply each element in the row in A by the corresponding element in the column in B, and sum the products. That's your element in AxB.

Anonymous

Matrix multiplication is not commutative, which throws off a lot of beginners

AdmBorkBork

4:31 PM

It also has restrictions on the sizes.

DJMcMayhem

CMC: given a list of integers, return 3 distinct values depending on whether the list is Strictly Increasing, Strictly decreasing, or neither.

Anonymous

@AdmBorkBork Yep, which I provided in the definition I gave

AdmBorkBork

Yeah, just reiterating.

Anonymous

@DJMcMayhem Actually, 7 bytes: ;S;R2╟í

Anonymous

Oh wait that doesn't satisfy the strictly requirement

Riker

4:36 PM

@Dennis what chef interpreter does TIO use? the python or perl one?

AdmBorkBork

Yeah, I was going to dupe-hammer it as this one, but the strictly part makes it slightly different.

Anonymous

@DJMcMayhem Actually, 12 bytes: ;;S;R2╟íu@═*

DJMcMayhem

@AdmBorkBork and the lack of monotone

dzaima

@DJMcMayhem APL, 19 bytes: {(⊃t)×∧/2=/t←×2-/⍵}

DJMcMayhem

Thanks @randomupvoter

@AdmBorkBork How do you dupehammer in chat?

AdmBorkBork

4:39 PM

Doesn't monotone here just mean it's "always" strictly increasing/decreasing, which is implied in your CMC?

Dennis

@Riker The Perl one. Clicking on the language name on TIO links to it.

Riker

oh, thanks

Adám

@DJMcMayhem APL (Dyalog Unicode), 16 bytes (0 0)(1 1)⍳⊂2</⎕

moonheart08

I'm going to need a healthy dose of magic, and a bit of hope, to work with this library, even if it does help make the contexts safer (which helps a lot).

DJMcMayhem

@AdmBorkBork Oooh, I thought it meant increasing or decreasing by one

Manish Kundu

4:43 PM

Hi.

dzaima

@Adám doesn't that only work with 3-element arrays?

AdmBorkBork

@DJMcMayhem Bold italics screamed in CAPITAL LETTERS

Dennis

> Method found by DrMcMoylex.

DJMcMayhem

@Dennis Who's that guy? What a weird name, geez

dzaima

APL, 18 16 bytes: (⊃t)×1=≢t←∪×2-/⎕

mudkip201

4:47 PM

Pyt, 7 bytes: ₋±Đ≡*0⦋

Returns 1 if strictly increasing, -1 if strictly decreasing, and 0 otherwise

Anonymous

Jelly question because I'm dense: suppose I have a dyad a with arguments x (left) and y (right). I want to call xay where ay is mapped over the elements of x. I thought it would just be xa"y, but that doesn't seem to work. What am I doing wrong?

caird coinheringaahing

xay$€ or xa€y

Dennis

" zips. You want € (each).

Anonymous

@cairdcoinheringaahing I thought I had tried that before, but apparently not. xa€y worked.

caird coinheringaahing

Got it right the first time :P

Anonymous

4:56 PM

@Dennis Ah, I was confused by vectorize in the docs.

Dennis

If a vectorizes, you don't need the €.

Anonymous

It does not

Anonymous

Ok, got that part working but I am limited by my lack of Jelly skills, the distracting pain in my shoulder, and my inability to focus caused by meds I took for said shoulder pain, so I'm going to stop trying :P

Dennis

What are you trying to do?

Anonymous

Solve that CMC

caird coinheringaahing

5:09 PM

watches Dennis get a 5 byte answer

Dennis

Lucky guess.

caird coinheringaahing

Wait, for real? You got a 5 byte answer? :D

Dennis