GUI music editor Updated 2025-07-16
Rail transport in Great Britain Updated 2025-07-16
Raised and lowered indices Updated 2025-07-16
TODO what is the point of them? Why not just sum over every index that appears twice, regardless of where it is, as mentioned at: www.maths.cam.ac.uk/postgrad/part-iii/files/misc/index-notation.pdf.
Those in indices on bottom are called contravariant vectors.
It is possible to change between them by Raising and lowering indices.
The values are different only when the metric signature matrix is different from the identity matrix.
Ciro's Edict #4 Further improvements to the website's base technology Updated 2025-07-16
github.com/cirosantilli/node-express-sequelize-nextjs-realworld-example-app contains the same baseline tech as OurBigBook, and I have been use to quickly test/benchmark new concepts for the website base.
I'm almost proud about that project, as a reasonable template for a Next.js project. It is not perfect, notably see issues on the issue tracker, but it it quite reasonable.
The side effects of ambitious goals are often the most valuable thing achieved once again? I to actually make the project be more important thatn the side effects this time, but we'll see.
Since the last update, I've made some major improvements to the baseline tech of the website, which I'll move little by little into OurBigBook. Some of the improvements actually started in OurBigBook.com. The improvements were:
- got a satisfactorily comprehensive linting working at: this commit. Nothing is easy, not even that! Part of the wisdom extracted to: stackoverflow.com/questions/58233482/next-js-setting-up-eslint-for-nextjs/70519682#70519682.
- fully rationalized directory structure to avoid nasty errors that show up in Next.js when accidentally requiring backend stuff on the client. Commit. A detailed explanation of this was extracted to: stackoverflow.com/questions/64926174/module-not-found-cant-resolve-fs-in-next-js-application/70363153#70363153.
- create an extremely clean and rationalized way to do API tests from a simple
npm test. These now actually start a clean server, and make full HTTP requests to that server. Commit. Wisdom extracted to: stackoverflow.com/questions/63762896/whats-the-best-way-to-test-express-js-api/70479940#70479940. - greatly reduce the number of SQL queries, fully understood every problem
- more intelligently using JOINs where I have managed to get Sequelize to do what I fucking want. This also led to several sequelize Stack Overflow answers as usual: stackoverflow.com/search?tab=newest&q=user%3a895245%20%5bsequelize%5dEverything that I didn't manage to do because of crappy sequelize is documented at: github.com/cirosantilli/node-express-sequelize-nextjs-realworld-example-app/issues/5
- better understanding Next.js/React/useSWR do avoid doing double API queries
System of ordinary differential equations Updated 2025-07-16
Triangle Updated 2025-07-16
Imaginary number Updated 2025-07-16
Rank of an elliptic curve over the rational numbers Updated 2025-07-16
Mordell's theorem guarantees that the rank (number of elements in the generating set of the group) is always well defined for an elliptic curve over the rational numbers. But as of 2023 there is no known algorithm which calculates the rank of any curve!
It is not even known if there are elliptic curves of every rank or not: Largest known ranks of an elliptic curve over the rational numbers, and it has proven extremely hard to find new ones over time.
TODO list of known values and algorithms? The Birch and Swinnerton-Dyer conjecture would immediately provide a stupid algorithm for it.
Great circle Updated 2025-07-16
Operating system Updated 2025-07-16
Superconductor I-V curve Updated 2025-07-16
Microorganism Updated 2025-07-16
Prime power Updated 2025-07-16
Subgroup generated by a group Updated 2025-07-16
Tree (data structure) Updated 2025-07-16
Vertebrate Updated 2025-07-16
Weighted graph Updated 2025-07-16
Computer hardware Updated 2025-07-16
Domain of a function Updated 2025-07-16
Dragon boat Updated 2025-07-16
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