Vancouver Island, British Columbia, Canada


After a few days in beautiful Vancouver, Rémi and I rented a car to undertake a road trip around British Columbia and Washington. First destination is Vancouver island. To get there, a ferry will have to take us through the beautiful Horsehoe bay.

Horseshoe bay in fjord

Vancouver island is a pretty awesome place for a road trip, as its hilly landscapes include beautiful lakes. At the end of the Ucluelet peninsula is our first stop for a nice walk along the Pacific Ocean.

But the best is yet to come as we drive up close to Tofino. We stop before the city to halt on a breathtaking beach. This beach will have us silently speechless for hours, until the sunset and despite the rain…

Tofino beach on island

Beach near Tofino

Rémi at sunset near Tofino

Surfer at Sunset

Rain at Sunset

Not much to add, is there?


The Beauty of Ellipses, Parabolas and Hyperbolas – S4A

The Beauty of Ellipses, Parabolas and Hyperbolas (via

Conics formed the chapter I hated the most in my undergrads. But that’s because exercices involve plenty of horrible algebraic computations. In this article, I’m proposing to just gaze at their beauty, their amazing mathematical properties and their…

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Chebika, Tamerza and Mides, Tunisia


First stop of this day road trip around Tozeur with 3 other friends in Southern Tunisia is Chebika, a small oasis on a hill in the middle of the desert plane. So cute!


After a visit of this beautiful isolated place near the border with Algeria, we took the car to head to Tamerza. Landscapes were breathtaking, as we were guided by my Tunisian friend Khaled.

Khaled and I on our way to Tamerza

cascade de tamerza

Benoît and I under waterfalls

Slightly before arriving to Tamerza, we visited its renowned water falls. On this warm winter day, Benoît and I decided to enjoy the freshness of the water!

Tamerza was fabulous. Lying in a small valley through which a river flows, it is filled by palm trees. Brilliant!

Sylvain at tamerza

Finally, the day ended by Mides Canyon, a few hundreds of meters away from the Algerian border. A last amazing sight of the breathtaking desert of Tunisia!

Mides Canyon

Gunung Semeru, Indonesia


At 2am, rain on the tent woke me up. What a scary thought! The day before, I had hiked all day long, alone, and camped in Kalimati, at 2,900 meters of elevation, at the foot of the gigantic Gunung Semeru, Java’s highest peak. I couldn’t bear the thought of ending this promising hike in the rain and with poor visibility. But there was no much I could do, so I kept sleeping…


When I woke up, I quickly opened the tent to figure out whether it was still raining. And there was a big blue cloudless sky! But as I tried to get out of the tent, I really woke up: I had been dreaming! So I kept sleeping… And this quirky dream occurred again! And a third time! I guess I was just so excited and scared that I kept dreaming about the instant of my waking up! And, yes, I did wonder if I weren’t in some inception movie…

Eventually, at 5:30am, I did wake up, for real… And it was sunny! I quickly got out of the tent and started hiking, leaving the tent and most of my stuffs behind. Once again, I probably was too excited, which partly explains why I then got lost several times! After an hour or so, I discovered that I was actually above a breathtaking sea of clouds! Amazing!

Sea of Clouds in Semeru

The Semeru Trail

Around 7:20 am, I got to the final section of the hike. I had just got out of the forest and was faced with a steep extremely sandy climb! What a horror! Every step was followed by a two-step sand-slide backwards. The only way to actually go up was to rush upwards. But this was so exhausting that I had to stop and have a break every 2 minutes. Overall, it took me 1 hour and 40 minutes to climb the remaining 1.5 km. That’s not too bad as some maps, like the one on the right, announce a 3-hour climb…

At 9am, I had made it! At 3,676 meters of elevation, I was on top of the Java island!

Semeru summit

Indonesian group on Semeru

A group of Indonesian people then invited me to share tea and cookies. This was a unique extremely convivial moment on top of the world, with some of the nicest persons you will ever find. A truly privileged moment.

But this moment was about to be topped by another one. Out of sudden, the volcano, which in fact is located a few hundreds meters away, exploded! A huge noise was followed by an eruption of gases! Legendary!


The Semeru actually erupts every 30 minutes. However, its gases are toxic, and it’s thus recommended not to spend too much time up there. Find out more about my Indonesian trip!




Last June, I had my first lonesome 3-week trip in Indonesia, from West Java to Lombok. It was a bit frightening beforehand, but 3 weeks felt way too short afterwards! What’s so cool about traveling alone is the freedom of undertaking pretty much anything that comes to our minds, leading to amazing stories.

Here are 15 peculiar things that happen to me…
– Meeting a Singapore-Chinese man who wants me to call him for any problem I face.
– Getting invited at lunch by Indonesian strangers.
– Playing Heal the World with angklung.
– Having an Indonesian biker taking me to bus station when I was lost at 4am. For free!
– Sharing a scrammed tiny van with my huge backpack and a dozen kids going to school.
– Taking 1 taxi, 4 buses, 1 angkot, 1 pick-up, 1 ojek and 1 becak in a single day.
– Having a Frenchman driving me to the bus station and inviting me to his house.
– Meeting 6 Indonesian hikers on a hike, and again two days later in a city.
– Repeating “Tidak Indonesia” all day long. Hearing “Oh Vietnam!” all day long.
Sharing cookies and teas with Indonesian strangers at 3676m elevation while watching eruptions of a volcano.
– Making friends with a Lithuanian couple to whom I introduced mechanism design and Poincaré conjecture.
– Getting a ride in a truck, right behind the driver.
– Having breakfast served in tent at 2:30 am when it’s cold and windy outside.
– Being awaked by barking dogs on a beach at 4am.
– Hiking 7 volcanoes, including 5 in 6 days representing over 100km of hike.


Plus, Indonesia is just one of these awesome countries with infinite breathtaking natural wonders! So far, on this blog, I’ve only written about the Rinjani rim and Gunung Semeru.

Facebook’s Crappy News Feed


I’ve recently found out about how facebook organized news feeds with his algorithm edge rank, thanks to this great YouTube video (in French). I know Facebook keeps secret some parts of the algorithm and I don’t understand its algorithm entirely, but, as an applied mathematician, I am appalled by how much the approach of the algorithm sucks.

My own experience as a user already made this fact obvious to me: My google chrome often suggests a translation of my facebook news feed page from Italian, Arabic or Thai! Facebook, can’t you know I don’t speak any of these languages? I never press the like button of these messages, nor do I comment them? More straightforwardly, I even tell you what languages I speak in my facebook profile!

Capture d’écran 2013-07-12 à 18.20.53

Now, how does the current edge rank work? In short, for each comment or like, the score of a post is added a product of the affinity between the commenter and the viewer, the kind of content of the post/comment/like and the recentness of the comment. This sounds pretty much like how I talk Spanish: let’s try some words and, hopefully, people will guess what I mean… It might work, but it’s not good!


So, how would an applied mathematician tackle the problem of organizing the news feed? That’s the interesting question! Well, there are plenty of different ways. Let me tell you how I would approach this problem.

First, to compare algorithms between each other, a measure of the quality of a news feed must be defined. And, fortunately, facebook already has what it takes to do so! Yes, I’m talking of this awesome like button, and there’s also the comment section. If there are images, videos or links, the quality of the news feed can also be measured by the number of clicks made by the user. I let your imagination work out the details…

What I’m talking about here is the definition of an objective function, which is the essential first step in optimization, as you can read it in my Science4All article on linear programming.

Second, let’s get to the algorithm itself. A basic approach would be based on machine learning. You can analyze the actions of the users on past posts to classify these posts into the ones the users liked, and those he didn’t like. Now involve a bunch of parameters which could explain that, such as, the content of the post, its language, a few keywords, its date, its number of likes, the authors of the likes, its comments… and insert that into a machine learning algorithm, and you’d get a much better ranking of the posts! The parameters can then even be adjusted by studying how they affects the objective function!

Find out more in my Science4All article on probabilistic algorithms!

Now, what I’m proposing here is the very basic approach. There are plenty of ways to do much much better! But facebook isn’t even doing that…

On a side note, Google Plus is so much more awesome with its news feed! If facebook doesn’t react, I wouldn’t be surprised to see Google outrunning facebook in the long run. On another side note, the friend suggesting algorithms of these websites also seem to really suck. I can’t understand why LinkedIn suggests people I have 1 or 2 relations in common, while there are still so many people out there with whom I share over 30 relations…

Thorsmork to Skogar, Iceland


I know my imagination is limited, but I have no idea how this day could ever be topped. The Thorsmork-to-Skogar hike was the final part of a tough and breathtaking 87km 3-day trek throughout Iceland’s volcanoes Rémi and I undertook.

The first day had got us through the indescribable Landamannalaugar and the single most beautiful sights I have ever seen. The second day had been a long and terribly exhausting walk through black sand deserts with constant rain to end up in a cute camp called Thorsmork.


In the early morning of the third and final day, my whole body was deeply hurt by the two previous days. My legs were sore, my shoulders were painful, my hips didn’t want to carry weights and you don’t want to see my feet… I was deeply doubting my capacity to finish the trek. Plus, after an hour or so, we lost the track.

But, then began an absolutely incredible hike up the mountains and volcanoes. All of sudden, I got miraculously empowered by the sheer awesomeness of the landscapes.

The Path up to Eyja

Surrounded by steep cliffs, weird plateaus, large valleys, green grass, black lava and blue glaciers, I felt unstoppable! I was transcended!

Hiking up to Eyja

P1020554 ManipV3_ISE

Around noon was the high point of the day in every possible sense! We walked through the lava flows of the 1-year-old eruption of the Eyjafjallajokull!

The lava was still red and smoking! Unbelievable!

This spectacular scenery was where we decided to have lunch to end a legendary morning!

Eyja Lava Flow

Then came the truly hard part of this hiking day. As we were running out of water and food, the fog took over. In a desert landscape with no visibility and a poorly marked track, all my pains rushed back to my body. At some point, the mere effort of putting one foot ahead of the other was extremely painful! Yet, while I was probably walking around 1km/h, somehow, I seemed to be outpacing Rémi! And this unbearable suffering went on for over three hours…


Until, suddenly, far in the horizon, out of nowhere, we saw houses in the plain! This was Skogar! We got there! We had made it!


Skogar Waterfalls

We took a final break to stare at the dramatic waterfalls the path was ending near to, while savoring the wonderful feeling of the accomplishment of a truly tough but extraordinary trek!

As we were peacefully sitting here, the numerous fellow awesome trekkers we had been hiking with all along were arriving one by one. They all had their fists raised, while I was rocked by the melodious sound of the phrase: What a day! What a day

The Thorsmork to Skogar hike is number 1 in my top 10 touristic visits.

You can see more amazing pictures of this hike in my Science4All article on the geological wonders of Iceland! Also, if you don’t want to hurt your body as much as we did, note that this trek can be done in up to 6 days, as recommended in many guides…