TransferWise Updated +Created
This is a good company, first they truly helped reduce international transfer fees. They they continued to morph into a decent challenger bank.
Their Wise Interest account was amazing as of late 2023: wise.com/gb/interest/
Instant access with representative national interests and 0.29% fees.
Brick and mortar banks were way way behind in that regard!
E.g. October 2023, Wise was doing 4.87% interest after fees, while Barclay's best option was 1.16% above 5k pounds on the Rainy Day Saver (5% below). Ridiculous!
JCVI-syn3A Updated +Created
essential metabolism for a minimal cell (2019) mentions:
JCVI-syn3A, a robust minimal cell with a 543 kbp genome and 493 genes, provides a versatile platform to study the basics of life.
Based on JCVI-syn3.0, they've added a few genes back to give better phenotypes, including slightly faster duplication time. Because the development cycle time is your God is also true in biology.
As of essential metabolism for a minimal cell (2019) it had only 91 genes of unknown function! So funny.
Bibliograpy:
Figure 1. Source. A description is present at: cdn.rcsb.org/pdb101/goodsell/2022_JCVI-syn3A.pdf Integrative Illustration of a JCVI-syn3A Minimal Cell by David Goodsell (2022) which describes everything in the picture.
OXAM Updated +Created
This is apparently where past exam papers can be found. Paywalled of course.
The paywall is stupid however, as they seem to provide past papers upon request, e.g.
This adds to the mess of having a different location for material per department. Presumably this exists because the central university authority wants to centralize examinations to have better control over degree requirements. If only they would also do the same for all materials and end the mess.
JavaScript is single threaded Updated +Created
async (JavaScript) Updated +Created
async is all present in JavaScript for two reasons:
How to teach Updated +Created
Off-the-shelf techniques to become a teaching superhero.
Customized website idea at: OurBigBook.com.
Discrete Fourier transform Updated +Created
Input: a sequence of complex numbers .
Output: another sequence of complex numbers such that:
Intuitively, this means that we are braking up the complex signal into sinusoidal frequencies:
  • : is kind of magic and ends up being a constant added to the signal because
  • : sinusoidal that completes one cycle over the signal. The larger the , the larger the resolution of that sinusoidal. But it completes one cycle regardless.
  • : sinusoidal that completes two cycles over the signal
  • ...
  • : sinusoidal that completes cycles over the signal
and is the amplitude of each sine.
We use Zero-based numbering in our definitions because it just makes every formula simpler.
Motivation: similar to the Fourier transform:
  • compression: a sine would use N points in the time domain, but in the frequency domain just one, so we can throw the rest away. A sum of two sines, only two. So if your signal has periodicity, in general you can compress it with the transform
  • noise removal: many systems add noise only at certain frequencies, which are hopefully different from the main frequencies of the actual signal. By doing the transform, we can remove those frequencies to attain a better signal-to-noise
In particular, the discrete Fourier transform is used in signal processing after a analog-to-digital converter. Digital signal processing historically likely grew more and more over analog processing as digital processors got faster and faster as it gives more flexibility in algorithm design.
Sample software implementations:
Figure 1.
DFT of with 25 points
. This is a simple example of a discrete Fourier transform for a real input signal. It illustrates how the DFT takes N complex numbers as input, and produces N complex numbers as output. It also illustrates how the discrete Fourier transform of a real signal is symmetric around the center point.
How to store data in the Bitcoin blockchain Updated +Created
There are apparently two methods:
Specific implementations:
Next.js example Updated +Created
Our examples are located under nodejs/next:
Solved ones:
P versus NP problem Updated +Created
Interesting because of the Cook-Levin theorem: if only a single NP-complete problem were in P, then all NP-complete problems would also be P!
We all know the answer for this: either false or independent.
Distribution (mathematics) Updated +Created
Generalize function to allow adding some useful things which people wanted to be classical functions but which are not,
It therefore requires you to redefine and reprove all of calculus.
For this reason, most people are tempted to assume that all the hand wavy intuitive arguments undergrad teachers give are true and just move on with life. And they generally are.
One notable example where distributions pop up are the eigenvectors of the position operator in quantum mechanics, which are given by Dirac delta functions, which is most commonly rigorously defined in terms of distribution.
Distributions are also defined in a way that allows you to do calculus on them. Notably, you can define a derivative, and the derivative of the Heaviside step function is the Dirac delta function.
Become famous through teaching Updated +Created
There is only one thing that can truly motivate you to make good materials: becoming famous.
Strive for that. Make good materials. Publish them. Get good reviews. Loop.
This generates a virtuous loop, which makes you produce better and better material.
Explain why the subject is beautiful Updated +Created
And if you really can't make money from a subject, there is only one other thing people crave: beauty.
Inward Bound by Abraham Pais (1988) Updated +Created
The book unfortunately does not cover the history of quantum mechanics very, the author specifically says that this will not be covered, the focus is more on particles/forces. But there are still some mentions.
Display manager Updated +Created
Check which you you have:
systemctl status display-manager.service
Tested on Ubuntu 23.10 I see:
● gdm.service - GNOME Display Manager
     Loaded: loaded (/lib/systemd/system/gdm.service; static)
     Active: active (running) since Sun 2023-12-24 10:34:50 GMT; 23min ago
    Process: 1827 ExecStartPre=/usr/share/gdm/generate-config (code=exited, status=0/SUCCESS)
   Main PID: 1850 (gdm3)
      Tasks: 4 (limit: 71817)
     Memory: 6.8M
        CPU: 119ms
     CGroup: /system.slice/gdm.service
             └─1850 /usr/sbin/gdm3
which means I have GNOME Display Manager.
Invalid Bitcoin script Updated +Created
They appear to be included, with rationale that you can already include syntactically valid crap in an unprovable way: github.com/bitcoin/bitcoin/issues/320 Better then have syntactically invalid crap that is provable.
The outputs of this transaction seem to be the first syntactically incorrect scripts of the blockchain: blockchain.info/tx/ebc9fa1196a59e192352d76c0f6e73167046b9d37b8302b6bb6968dfd279b767?format=json, found by parsing everything locally. The transaction was made in 2013 for 0.1 BTC, which then became unspendable.
The first invalid script is just e.g. "script":"01", which says will push one byte into the stack, but then ends prematurely.
Dot product Updated +Created
The definition of the "dot product" of a general space varies quite a lot with different contexts.
Most definitions tend to be bilinear forms.
We use the unqualified generally refers to the dot product of Real coordinate spaces, which is a positive definite symmetric bilinear form. Other important examples include:
The rest of this section is about the case.
The positive definite part of the definition likely comes in because we are so familiar with metric spaces, which requires a positive norm in the norm induced by an inner product.
The default Euclidean space definition, we use the matrix representation of a symmetric bilinear form as the identity matrix, e.g. in :
so that:
Dual space Updated +Created
The dual space of a vector space , sometimes denoted , is the vector space of all linear forms over with the obvious addition and scalar multiplication operations defined.
Since a linear form is completely determined by how it acts on a basis, and since for each basis element it is specified by a scalar, at least in finite dimension, the dimension of the dual space is the same as the , and so they are isomorphic because all vector spaces of the same dimension on a given field are isomorphic, and so the dual is quite a boring concept in the context of finite dimension.
One place where duals are different from the non-duals however is when dealing with tensors, because they transform differently than vectors from the base space .

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