Python library for Bullet Physics.

Became very popular as of result of people using Bullet Physics for reinforcement learning AI training robot simulations.

Website: pybullet.org/

Source code: somewhere inside the main Bullet Physics source tree. Yay.

The period does depend on the initial height/angle, except for the very small angle approximation:

Like Jimmy Wales, he used to work in finance and then quit. What is it with those successful e-learning people??

One of the Millennium Prize Problems.

See also: existence and uniqueness of solutions of partial differential equations.

Many subjects have changed very little in the last hundred years, and so it is mind-blowing that people have to pay for books that teach them!

If computers are bicycles for the mind, Ciro wants this website to be the Ferrari of the mind.

Since Ciro Santilli was young, he has been bewildered by the natural sciences and mathematics due to his bad memory.

The beauty of those subjects has always felt like intense sunlight in a fresh morning to Ciro. Sometimes it gets covered by clouds and obscured by less important things, but it always comes back again and again, weaker or stronger with its warmth, guiding Ciro's life path.

As a result, he has always suffered a lot at school: his grades were good, but he wasn't really learning those beautiful things that he wanted to learn!

School, instead of helping him, was just wasting his time with superficial knowledge.

First, before university, school organization had only one goal: put you into the best universities, to make a poster out of you and get publicity, so that more parents will be willing to pay them money to put their kids into good university.

Ciro once asked a chemistry teacher some "deeper question" after course was over, related to the superficial vision of the topic they were learning to get grades in university entry exams. The teacher replied something like:Ciro feels that this was one of the greatest compliments he has ever received in his life. This teacher, understood him. Funny how some things stick, while all the rest fades.

Another interesting anecdote is how Ciro Santilli's mother recalls that she always found out about exams in the same way: when the phone started ringing as Ciro's friends started asking for help with the subjects just before the exam. Sometimes it was already too hopelessly late, but Ciro almost always tried. Nothing shows how much better you are than someone than teaching them.

Then, after entering university, although things got way better because were are able to learn things that are borderline useful.

Ciro still felt a strong emotion of nostalgia when after university his mother asked if she could throw away his high school books, and Ciro started tearing them all down for recycling. Such is life.

University teachers were still to a large extent researchers who didn't want to, know how to and above all have enough time and institutional freedom to teach things properly and make you see their beauty, some good relate articles:

The very fact that you had very little choice of what to learn so that a large group can get a "Diploma", makes it impossible for people to deeply learn what the really want.

This is especially true because Ciro was in Brazil, a third world country, where the opportunities are comparatively extremely limited to the first world.

Also extremely frustrating is how you might have to wait for years to get to the subject you really want. For example, on a physics course, quantum mechanics is normally only taught on the third year! While there is value to knowing the pre-requisites, holding people back for years is just too sad, and Ciro much prefers backward design. And just like the university entry exams, this creates an entry barrier situation where you might in the end find that "hey, that's not what I wanted to learn after all", see also: students must have a flexible choice of what to learn.

We've created a system where people just wait, and wait, and wait, never really doing what they really want. They wait through school to get into university. They wait through university to get to masters. They wait through masters to get to PhD. They wait through PhD to become a PI. And for the minuscule fraction of those that make it, they become fund proposal writers. And if you make any wrong choice along the, it's all over, you can't continue anymore, the cost would be too great. So you just become software engineer or a consultant. Is this the society that we really want?

And all of this is considering that he was very lucky to not be in a poor family, and was already in some of the best educational institutions locally available already, and had comparatively awesome teachers, without which he wouldn't be where he is today if he hadn't had such advantages in the first place.

But no matter how awesome one teacher is, no single person can overcome a system so large and broken. Without technological innovation that is.

The key problem all along the way is the Society's/Government's belief that everyone has to learn the same things, and that grades in exams mean anything.

Ciro believes however, that exams are useless, and that there are only two meaningful metrics:

Even if you wanted to really learn natural sciences and had the time available, it is just too hard to find good resources to properly learn it. Even attending university courses are hit and miss between amazing and mediocre teachers.

If you go into a large book shop, the science section is tiny, and useless popular science books dominate it without precise experiment descriptions. And then, the only few "serious" books are a huge list of formulas without any experimental motivation.

And if you are lucky to have access to an university library that has open doors, most books are likely to be old and boring as well. Googling for PDFs from university courses is the best bet.

Around 2012 however, he finally saw the light, and started his path to Ciro Santilli's Open Source Enlightenment. University was not needed anymore. He could learn whatever he wanted. A vision was born.

To make things worse, for a long time he was tired of seeing poor people begging on the streets every day and not doing anything about it. He thought:which like everything else is likely derived subconsciously from something else, here Schindler's list possibly adapted quote from the Talmud:

So, by the time he left University, instead of pursuing a PhD in theoretical Mathematics or Physics just for the beauty of it as he had once considered, he had new plans.

We needed a new educational system. One that would allow people to fulfill their potential and desires, and truly improve society as a result, both in rich and poor countries.

And he found out that programming and applied mathematics could also be fun, so he might as well have some fun while doing this! ;-)

So he started Booktree in 2014, a GitLab fork, worked on it for an year, noticed the approach was dumb, and a few years later started building this new version. The repo github.com/booktree/booktree is a small snapshot of Ciro's 2014 brain on the area, there were quite a few similar projects at the time, and most have died.

Ciro is basically a librarian at heart, and wants to be the next:

I guess you also have to change the sign of the gravitational constant?

Bibliography: