Ciro Santilli @cirosantilli 35

Managed to upload the content from the static website cirosantilli.com (OurBigBook Markup source at github.com/cirosantilli/cirosantilli.github.io) to ourbigbook.com/cirosantilli.

Although most of the key requirements were already in place since the last update, as usual doing things with the complex reference content stresses the system further and leads to the exposition of several new bugs.

The upload of OurBigBook Markup files to ourbigbook.com was done with the newly added OurBigBook CLI ourbigbook --web option. Although fully exposed to end users, the setup is not super efficient: a trully decent implementation should only upload changed files, and would basically mean reimplementing/using Git, since version diffing is what Git shines at. But I've decided not to put much emphasis on CLI upload for now, since it is expected that initially the majority of users will use the Web UI only. The functionality was added primarily to upload the reference content.

This is a major milestone, as the new content can start attracting new users, and makes the purpose of the website much clearer. Just having this more realistic content also immediately highlighted what the next development steps need to be.

Once v1.0 is reached, I will actually make all internal links of cirosantilli.com to point to ourbigbook.com/cirosantilli to try and drive some more traffic.

The new content blows up by far the limit of the free Heroku PostgreSQL database of 10k lines. This meant that I needed to upgrade the Heroku Postgres plugin from the free Hobby Dev to the 9 USD/month Hobby Basic: elements.heroku.com/addons/heroku-postgresql, so now hosting costs will increase from 7 USD/month for the dyno to 7 + 9 = 16 UDS/month. After this upgrade and uploading all of cirosantilli.com to ourbigbook.com, Heroku dashboard reads reads:so clearly if we are ever forced to upgrade plans again, it means that a bunch of people are using the website and that things are going very very well! Happy how this storage cost turned out so far.

One key limitation found was that Heroku RAM memory is quite limited at 512MB, and JavaScript is not exactly the most memory economical language out there. Started investigation at: github.com/ourbigbook/ourbigbook/issues/230 Initially working around that by simply splitting the largest files. We were just on the verge of what could be ran however luckily, so a few dozen splits was enough, it managed to handle 70 kB OurBigBook Markup inputs. So hopefully if we manage to optimize a bit more we will be able to set a maximum size of 100 kB and still have a good safety margin.

The courses are highly open, almost everything is given publicly except solutions, many of which are given to teachers only. Well done!

Past exam papers index: www.cl.cam.ac.uk/teaching/exams/pastpapers/

Isomers were quite confusing for early chemists, before atomic theory was widely accepted, and people where thinking mostly in terms of proportions of equations, related: Section "Isomers suggest that atoms exist".

Things to do:

One of the saving graces of open source is that you ship shit, but you don't announce vaporwave.

A recreational computer simulation!

Although Ciro Santilli is a big fan of plaintext files and of Vim, not so for games. Games must be easy to understand since they are just a toy.

Tilesets to the rescue!

Made the website navbar and article lists more mobile friendly. Main motivation: improvised demos to people I meet IRL!

Following the definition of the indefinite orthogonal group, we want to show that only the metric signature matters.

First we can observe that the exact matrices are different. For example, taking the standard matrix of $O(2)$:and:both have the same metric signature. However, we notice that a rotation of 90 degrees, which preserves the first form, does not preserve the second one! E.g. consider the vector $x=(1,0)$, then $x\cdot x=1$. But after a rotation of 90 degrees, it becomes $x_2=(0,1)$, and now $x_2\cdot x_2=2$! Therefore, we have to search for an isomorphism between the two sets of matrices.

For example, consider the orthogonal group, which can be defined as shown at the orthogonal group is the group of all matrices that preserve the dot product can be defined as:

TODO vs all the others?