11.15.1 Top new questions this week

11.15.1.1 Boids by Simon Woods: can we re-invent further efficient flocking models to forge complexity from simple rules?
11.15.1.2 Why is 2-dimensional array access slow (compared to memoized downvalues)?
11.15.1.3 How to run tests for Mathematica package on GitHub actions?
11.15.1.4 A. L. Crego "Traces" video art reproduction
11.15.1.5 How is Out[] set?
11.15.1.6 Performance in front-end workflows and non/zero $HistoryLength
11.15.1.7 Retrieving connected components from list of neighbors
11.15.1.1 Boids by Simon Woods: can we re-invent further efficient flocking models to forge complexity from simple rules?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312395

It has been 12 years since @simon-woods created this fascinating animation an invented a boids model which is more efficient than typical ones. Code is extremely short an elegant: 
 
... 
[graphics] [animation] [simulation] [modeling]
 
asked by Vitaliy Kaurov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=13 Score of 23
answered by Craig Carter https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=12461 Score of 18
11.15.1.2 Why is 2-dimensional array access slow (compared to memoized downvalues)?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312377

The fabricated example below demonstrates a bizarre case I ran into. (If it matters, this is with Mma 14.1 on Apple ARM, but I see the same behavior with Mma 12.3.1 on Intel x86.) 
On a whim, I tried ... 
[memoization] [packed-arrays] [downvalues] [array]
 
asked by Alexander Perlis https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=60048 Score of 11
answered by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 Score of 4
11.15.1.3 How to run tests for Mathematica package on GitHub actions?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312372

How can tests be set up to run on GitHub actions for a Mathematica package? 
I am looking for a complete guide or perhaps a live example. 
This might be possible with the Free Wolfram Engine, but it is ... 
[packages] [testing-and-verification] [free-wolfram-engine] [development] [continuous-integration]
 
asked by Szabolcs https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=12 Score of 8
11.15.1.4 A. L. Crego "Traces" video art reproduction

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312354

I saw this recent art "Traces" by A. L. Crego - check original at the link, ecause animated GIF here is low quality: 
 
I cannot figure out what makes it look like it does. I guess we could ... 
[graphics] [animation] [generative-art] [video]
 
asked by Vitaliy Kaurov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=13 Score of 7
11.15.1.5 How is Out[] set?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312453

From Out[]: 
 
 %n  or  Out[n] 
is a global object that is assigned to be the value produced on the $n^{\text{th}}$ output line. 
... 
[evaluation]
 
asked by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 Score of 6
11.15.1.6 Performance in front-end workflows and non/zero $HistoryLength

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312458

What explains the difference in timing? 
... 
[performance-tuning] [evaluation]
 
asked by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 Score of 6
answered by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 Score of 8
11.15.1.7 Retrieving connected components from list of neighbors

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=312444

I have a list of vertices (denoted by integers) with larger index that each vertex connects to, like below: 
... 
[list-manipulation] [graphs-and-networks]
 
asked by qwerty https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5861 Score of 4
answered by Henrik Schumacher https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=38178 Score of 2