Public Google+ posts of Arnaud Chéritat.

Categories: Opinions, humour or public

10 Sep 2018
Again, today's smbc and xkcd resonnate.
03 Sep 2018
Why do I have the feeling that something has gone wrong with my TeX style?
Activity: was plussed 2 times
10 Aug 2018
"Quelle est la distance moyenne séparant les objets de la ceinture de Kuiper ?"
Intéressante question du public lors d'un "café débat" au 28e Festival d'Astronomie de Fleurance.

Réponse avisée d'un des chercheurs (Sébastien Rodriguez, je crois) : "ces objets sont tellement petits par rapport à la distance les séparant que la probablilité qu'une sonde spatiale traversant cette ceinture heurte un objet accidentellement est pratiquement nulle".

J'aimerais apporter un avis personnel sur la question.

En bref : la réponse n'est pas tellement un nombre mais plutôt... une courbe.

En pas bref :

1. Qu'entend-on par la distance moyenne ?

a. Si on cherche à calculer la moyenne sur toutes les paires d'objets de la valeur de leurs distance, on obtient un résultat pas très intéressant, puisqu'il sera de l'ordre du rayon de la ceinture.

b. Donc ce qu'on veut calculer en réalité c'est la moyenne sur tous les objets de sa distance à l'autre objet le plus proche.

2. Quid de la réponse ?

Fait : On lit sur Wikipedia que le nombre d'objet de diamètre D est de l'ordre de 1/D^4 : par exemple il y a 10000x plus d'objets de taille 1km que d'objets de taille 10km, et 10000x plus d'objets de taille 100m que de taille 1km, etc...

Résultat : la distance moyenne dépend fortement de D.

En fait si vous réduisez D à la taille d'un atome... Vous avez une distance moyenne de l'ordre... du centimètre !
09 Aug 2018
Japan space agency finds one of the planets of Le Petit Prince
Activity: was plussed 1 time
19 Mar 2018
Activity: was plussed 3 times
06 Dec 2017
smbc and xkcd mentioned self-loathing on the same day
29 Oct 2017
Activity: was plussed 2 times
15 Sep 2017
Activity: was plussed 3 times
19 Aug 2017
I've been programming in Javascript these days and the most common error I got was

SyntaxError: missing ; before statement

but this is quite misleading because most of times my mistake was not to forget a semicolon but to use "var" instead of "function" in front of a function definition.

i.e. I tend to write the following but it is incorrect

var f(...) {};
var f(...) = { ... };

the following can be used

function f(...) { ... };
var f = function(...) { ... };
Activity: was plussed 1 time

Ilies Zidane: When assigning a function to a variable (function expression), you need the semicolon!


var f = function(...) {...};

Arnaud Chéritat: +Ilies Zidane : in theory yes, however js is tolerant on the semicolon and very often you can avoid it. If I write
var f = function(...) {...}
it is accepted (I don't know the rule here for a valid omission, maybe it depends on what follows).
If I write
var f(...) = { ... };
it is not accepted and complains about missing semicolon.

Ilies Zidane: The interpreter is trying to parse a variable definition (usually terminated by a semicolon) and failing as you are defining a function.

In JS semicolons can be ommited if the statment is followed by a line break or it is the last statment in a block { }. But highly recommanded to use them all the time as some statments might be intepreted badly:




Arnaud Chéritat: Thank you for this clarification of the ; ommission. I have updated my post to avoid ambiguity.

18 Aug 2017
On Wikipedia's article on black dwarf stars there's a humorous(?) illustration
Note: the image is not actually 100% black.

I was following chains of links on the Wikipedia after reading the excellent one on the far future of Humanity, life on Earth and the Universe pointed out by Ian Agol here a few days ago.
Fun fact: it turns out the universe is too young since the Big Bang right now so there are no black dwarf stars yet.
Activity: was plussed 3 times
09 Jun 2017
You're visiting France from US/UK and having trouble adapting to the local keyboard?

Could be worse...
Activity: was plussed 1 time
09 Jun 2017
"Are you agree?"

Hurray! Maybe ten years after many other cities and countries, the Toulouse Blagnac airport finally offers free Wi-Fi.

Obviously the login page in English language has been written by a native French speaker.
09 Jun 2017
Another thought about the future norm for French keyboards just stroke me.

France finally decides to normalize the layout of mechanical keyboards for French language. But for years there has been signs that mechanical keyboards are in danger of disappearing, now that more and more devices are purely tactile and understand voice.
09 Jun 2017

Pour me changer d'une actualité saturée de politique depuis 4 mois, je lisais hier soir ce document intitulé "Vers une norme française pour les claviers

Mais même là...
27 Feb 2017
I just received this email :

"[...] It is our great pleasure and privilege to welcome you to join the 8th World Gene Convention-2017, [...] We would like to welcome you to be the chair/speaker in Theme 902: Agriculture, Food and Plant Biotechnology while presenting about A proof of the Marmi–Moussa–Yoccoz conjecture for rotation numbers of high type [...]"

How embarrassing. I indeed published this article, but... I it is about pure math, my work has nothing to do with agriculture.They add :

"If the suggested thematic session is not your current focused core, you may look through the whole sessions and transfer another one that fit your interest (more info about the program is available at [...]"

phew, I'm relieved
Activity: was plussed 4 times, reshared 1 time

Travis Waddington: Aww, I was excited to read about exciting new applications of holomorphic dynamics to agriculture. As far as I know, the field has been stagnant since Milnor's seminal article, "On the concept of a tractor".

14 Feb 2017
That's just amazing.
Activity: was plussed 1 time
14 Dec 2016

10 Nov 2016
Planet Mars had correctly predicted the outcome of the 2016 election in USA.

(authentic image from the Indian Space Research Organization taken by Mars Orbiter Mission on October 1st, 2014, see
05 Nov 2016
A few years ago MathSciNet used to reference a prolific Mathematician called "et al." with 518 publications, but removed it for a mysterious reason. Fortunately I took screen shots.

btw these are authentic screenshots
Activity: was plussed 2 times

Namig Guliyev: But that "author" still has a Google Scholar profile:

03 Nov 2016
I always found Blender's user interface unfriendly. Today I discovered that Python scripting in Blender is even worse.

Afterthought: still, I'm glad that such free software exists.
Activity: was plussed 2 times
03 Nov 2016
I just translated one of my (very) short stories to English.

Ants living in a ribbon set off to explore the far west...

If you have 5mn* you may read it by clicking on the link below and tell me what you think.

*: Estimated reading time for an average reader.

- I wrote it 19 years ago when I was 22.
- It was eventually published together with another super-short story of mine by a small press Editor together with other French sci-fi short stories by non-professional writers like me.
- This earned me something like 25 euros (or was this 25 Francs?) because this was proportional to the number of pages and my two texts totalled 8 pages.
- If you can read French you may also have a look at my other three short stories ( and sorry for the look of the page, it dates from 1997!), I wrote them a long time ago, before inspiration left me.
Activity: was plussed 3 times, reshared 3 times
19 Sep 2016
27 Aug 2015
Painted but not yet varnished, they have a nice matte and soft looking texture. However, this is too fragile so varnish is needed.
Activity: was plussed 1 time

Ilies Zidane: Tada!

10 Apr 2012
Pendant ce temps, sur Google+...
(Meanwhile, on Google+)
Activity: was reshared 1 time

Ilies Zidane: Nice! C'est où ?

Arnaud Chéritat: Hangzhou, le lac de l'est (ou de l'ouest, j'ai oublié)

Fei Yang: C'est le lac de l'ouest ^_^