j_bertolotti

lisyarus, 5 days ago to random

Working more on the animations while I feel the inspiration. Improved walking cycle, put the instruments in the villagers' hands, added grass cutting & tree chopping.

I love how it immediately feels so much more alive

video/mp4

j_bertolotti, 6 days ago to godot

Super-noob #Godot question:
I have a very simple 2D platformer with a tilemap to make the background and the platform, and a character with basic movement. I know how to "paint" some of my tiles with the "physics layer" so the character can stand on them etc, but if I try to include a "rigidbody2d", it bounces against my charachter, but passes straight through the floor tiles. Let' s say I am baffled and have no clue which beginner mistake I am making.

gregeganSF, 8 days ago (edited 5 days ago) to random

Every solid object, such as the rods in the image below, has an inertia tensor. We can write the inertia tensor for the black rod, which keeps changing its orientation, as a sum of various multiples of the inertia tensors for the 6 fixed rods. The plot at the bottom shows how these 6 components change as the black rod points in different directions.

But why do we need 6 components? In 3D space, shouldn’t 3 be enough?

To see why we really need 6, let’s look at the inertia tensor. This is a matrix, I, that we use to multiply the angular velocity vector of an object, ω, to get the angular momentum, L.

The velocity of a point mass whose angular velocity is ω is given by:

v = ω × r

where r=(x,y,z) gives the coordinates of the point mass.

The linear momentum is:

p = m v = m ω × r

and the angular momentum is:

L = r × p = m r × (ω × r)

To get the same thing using matrices, note that we can write the cross product of r with any vector like ω as:

r × ω = C(r) ω

where C(r) is the matrix:

0 –z y
z 0 –x
–y x 0

This lets us write:

L = m r × (ω × r)
= –m r × (r × ω)
= –m C(r)^2 ω

Minus the square of the matrix C(r) is:

y^2+z^2 –xy –xz
–xy x^2+z^2 –yz
–xz –yz x^2+y^2

So the inertia tensor for a point mass is:

I = –m C(r)^2

This is the matrix above, multiplied by m.

In general, we add up (or integrate) over all the point masses in the body, to get the inertia tensor for the whole thing.

The inertia tensor we obtain this way will always be a symmetric matrix, so it can be specified with 6 numbers: 3 on the diagonal, and 3 above. So the inertia tensors belong to a 6-dimensional space.

eniko, 11 days ago to random

ive gotten enough practice at kitsune tails during development that maybe i'll speedrun it for a while after it launches

gregeganSF, 9 days ago to random

I wasn’t sure if any of these entries were jokes, but the most amusing one checks out as valid:

“A quasigroup with an idempotent element is called a pique ("pointed idempotent quasigroup")”

https://en.wikipedia.org/wiki/Quasigroup

The diagram is from:

https://x.com/arithmoquine/status/1798018671194829070

sio, 9 days ago to random Italian

Chi se lo sarebbe aspettacchio (io no)

j_bertolotti, 7 days ago to random

"Businesspeople are smart"
Well, some are and some aren't.
But I have yet to see any correlation between how smart they are and how much their company is valued.
https://arstechnica.com/gadgets/2024/06/report-humane-ai-pin-did-7-million-in-sales-wants-to-sell-for-1-billion

j_bertolotti, 9 days ago (edited 5 days ago) to random

In a sense Microsoft is right: schools should take responsibility for GDPR and data protection of their pupils, and stop using Microsoft products.
https://www.engadget.com/eu-accuses-micrsoft-of-secretly-collecting-childrens-data-124141294.html?src=rss

seamsay, 12 days ago to physics

Anyone on mathstodon got a better answer to this #physics question? I feel like somebody could do better than I did.

https://aus.social/

j_bertolotti, 1 month ago to random

#PhysicsFactlet: The "Ashcroft/Mermin Project"
I will try to (likely very slowly) go through the classic textbook "Solid State Physics" by Ashcroft and Mermin and make one or more animation/visualization per chapter.
This will (hopefully) help people digest the topic and/or be useful to lecturers who are teaching about it. As with all my animations, feel free to use them.
The idea is that the animations are a companion to the book, so I will give only very brief explanations here.

j_bertolotti, 10 days ago to machinelearning

If you are looking for a #PhD and are interested in working on #OpticalComputing for #MachineLearning (and to spend some time in the UK and some time in Australia), contact me!
Got the funding but the official advert is not out yet. Will update when it is (but the deadlines are going to be short).

j_bertolotti, 14 days ago to random

#VideoGameReview
A few days back I finished #Spiritfarer, and I have opinions.
If you don't know it, Spiritfarer is a 2020 resource management game with some platforming element. The general idea is that you are in a sort of land of the dead, and have to collect the spirits of the departed and take care of them until they feel ready to move on.
Let's start with the positives: this is 100% a "cosy" game with essentially no penalty for failing anything beside the time it takes to try again. It is also beautifully drawn and animated, and the idea that you have to keep piling weirdly shaped buildings on your boat gives it a very distinctive vibe.
Despite the fact that there are a large number of largely anonymous souls "living" in the archipelago the game is set in, you only help a relatively small number, and each of them has a well defined story and personality. The idea is that by the time you finally bring them to the "everdoor", you got attached to them and their departure feels emotional. Does it work? It depends. The souls cover a wide spectrum, and different people will resonate with some and not resonate with other. I personally only really felt for two of them (an old kind lady developing dementia and a young kid), but I understand that different people might get attached to different characters.
The moment to moment gameplay is largely about collecting resources, so you can build stuff that allows you to collect more and different resources. It is not a very original game loop, but it is well done and it works. For about half of the game.
Problem is, while you bring more souls to the everdoor, you have fewer souls to attend to, and after a while you find yourself with a ton of pointless stuff.

toddo, 15 days ago to random

One thing: I really wish the MSM would stop saying "hush money to a porn star" and "cover up an affair". He was convicted of ELECTIONS FRAUD. This matters. Having sex (barely consensual if it all) with a porn actor is NOT illegal, nor is lying about it to your wife. Spending campaign money to influence an election by manipulation of information and the media: Illegal. This is about elections and core democratic principles.

vicgrinberg, 16 days ago to random

I'm amazed by folks who have orderly office cupboard. This is my variant of as cleaned up as it gets 😅

#AboutToday

lisyarus, 16 days ago to random

In other news, made an icosahedron from coloured magnets

image/jpeg

MissingThePt, 17 days ago to random

You’ll have to pry my American paper out of my cold, dead hands.

QuantumWitch, 17 days ago to pixelart

Ren finds a spooky place, in Quantum Witch

#indiegame #indiedev #pixelart

j_bertolotti, 18 days ago to random

#PhysicsFactlet
The human eyes have "only" 3 different colour receptors, so multiple spectra can be perceived as the same colour.
(And this without considering all the ways the signal is processed before you actually "see" it.)
#Optics #Colour #Color #Vision

On the left, the absorption spectra of the 3 human colour receptors, with a varying spectrum (shown as a black line) on top. On the right a disk coloured with the RGB equivalent of that spectrum.