Scientific Computing

Matlab mustBeA is used in function argument validation to check that a variable is in one of multiple classes, instead of the single class coercion used by Matlab arguments block by default.

Simply create a file in the project directory “mustBeA.m”, or under private/mustBeA.m

function mustBeA(x, classes)
% for Matlab < R2020b
arguments
  x
  classes (1,:) string
end

mustBeMember(class(x), classes)

end

Matlab mustBeFile and mustBeFolder can fail to validate when the filename starts with a tilde “~”. Tilde is used by most terminal shells to indicate the user home directory. However, Matlab does not currently recognize tilde.

Workaround this issue with expanduser.m in the mustBe* call.

Example: myfun.m:

function myfun(A, B)
arguments
  A {mustBeA(A, ["string", "char"])}
  B (1,1) {mustBeNumeric}
end

...

end

A summary of public Windows Subsystem for Linux changes for the latest Windows Fast Ring build and recent builds is provided. A master listing of current build vs. Ring is also available.

Additional notes:

• Windows Subsystem for Linux release notes
• Windows Subsystem for Linux: About with link to issue trackers, presentations, etc.
• Microsoft Commandline Blog

Common web page / blog post applications where concealing text until the viewer clicks include:

• table of contents
• spoilers
• long details not all readers are interested in at that point in the article

This is implemented via the HTML5 details tag. This technique works for many Markdown-based sites such as GitHub (GitHub Issues click-to-reveal long debug text) and GitLab.

<details>
  <summary>click for spoilers</summary>

  <ul>
    <li>The season finale for Season 1 showed ...</li>
    <li>And season 2 opener revealed ...</li>
  </ul>
</details>

Example

IANA RFC8615 defines a “.well-known/” folder for web servers to put metadata fundamental to a web server’s organization, policies or contact information. Several popular files are seen under public website https://example.invalid/.well-known/ directory.

keybase.txt

verify ownership of domain for Keybase.io

security.txt

security incident contact info

dnt-policy.txt

Do Not Track Policy statement

humans.txt

author information

The 2020 movie “The Midnight Sky” is based on the 2016 Lily Brooks-Dalton book Good Morning, Midnight. I customarily approach book-based films by reading the book first. This review is only about the book.

I found the character-oriented narrative quite compelling, with multiple characters having development and reflection. The only slight downside to the book is as typical in most fiction (including post-apocalyptic and science fiction), the radio communications and vehicle aspects of the book could have been described more accurately by having a technical reviewer. I think the author did a better than average approach to the radio comms, minus the glitches noted below. I compliment the author’s approach–these slight issues are endemic in fiction books. Contradictions I notice involved transportation and radios comms.

A gasoline engine that has a pull rope start is subsequently described as having a dead battery and therefore unable to start. In fact, it’s possible in some cases to improvise a pull start on small electric start engines. Since another similar vehicle is described as having electric start, this may have been an editing mistake (perhaps the final intent was to have both vehicles be electric start).

The author’s ham radio callsign is used by a character–cute! The author could have more specifically addressed LEO satellite comms window for simplex VHF comms. The characters could simply say VHF / UHF, as it’s uncommon to spell out the abbreviated terms. There are frequent references to RF sine waves, when actually random noise was seemingly implied.

Modern scientific practices are concerned with obtaining results in a socially conscious and responsible manner, minimizing external impacts. Recent papers including Strubell, Ganesh, McCallum 2019 “Energy and Policy Considerations for Deep Learning in NLP arXiv note the energy consumption impacts of machine learning and AI. A tech ethics leader pushing for responsible AI was abruptly fired. Critical challenges in efficient food and packaging supply chains include plastic recycling, plastic ocean patches. and human factors such as child slavery in chocolate production. The American Geophysics Union (AGU) reorganized sections including Science and Society and GeoHealth oriented around the intersection science has with human well-being and government policies.

Companies increasingly use systems approaches to product quality and minimizing external costs. Goodnow Farms chocolate production of top-quality confectioneries considers the whole cacao lifecycle. Each chocolate type has an associated story and photo book showing the local farmer’s process.

Meson projects using Meson subprojects have a project directory structure like:

meson.build
main.c
subprojects/
  lapack/
  lapack.wrap

where “subprojects/lapack/” is automatically created as a Meson subproject from the metadata in “subprojects/lapack.wrap”. It’s desirable to ignore the subprojects code directories in Git.

For Meson subprojects, using the negate .gitignore syntax Git will ignore subdirectories but track the subprojects/*.wrap files, by including in the project top-level .gitignore:

/subprojects/*

!/subprojects/*.wrap

This technique can be applied to similar non-Meson scenarios.

NOTE: The .gitignore syntax has a precise meaning. For example, /subprojects/* means to ignore the directory contents of top-level directory “subprojects”, but not the directory itself. This is important for the next stanza !/subprojects/*.wrap, which means to not ignore files with .wrap suffix in top-level directory “subprojects”.

Thanks to @lunasorcery for pointing out the correct .gitignore syntax.

Empty files can be used as a mean to pass information between programs in a persistent manner, or a form of configuration. Empty files can be used on web servers to declutter 404 logs of endless bot scans.

For the examples below, we assume relative filename “path/to/empty”, where directories “path/to” already exist. We assume that a file does NOT exist at the filename, and it may be overwritten if it exists.

NOTE: For simplicity, some of these examples overwrite existing files, but some do not overwrite. Extra code is required to give a consistent behavior. All examples at least create an empty file if one doesn’t exist.

Windows users often use PowerShell. Create empty file with PowerShell (on any operating system):

New-Item path/to/empty

For Linux, macOS and other Unix-like systems, most shells create empty file like:

touch path/to/empty

Python creates an empty file by:

pathlib.Path('path/to/empty').touch()

Fortran creates an empty file by:

open(newunit=u, file='path/to/empty')
close(u)

Create an empty file in C++:

#include <fstream>

std::ofstream output("path/to/empty");

Those running a public web server are frequently subject to bot scans. While using best practices is the proper approach, there may still be a lot of 404 log results from bots. Declutter the log by redirecting bot URLs to a single zero-byte empty page while still returning code 404.

Another choice is to return HTTP status codes. Netlify only allows a few _redirects HTTP status codes. We redirect bot URLs to /bot.html and return a 404 code using an empty file.

Empty files: since these files are legitimate, but may not be used by your site, we create empty files for these:

favicon.ico
ads.txt
app-ads.txt

The Netlify _redirects file should be in the site publish directory. For Hugo it may be “public/_redirects”. We prefer the _redirects file to netlify.toml, because the redirect syntax is much more concise in _redirects files. Use Netlify Playground to instantly test file syntax.

A _redirects file for a Hugo blog may need editing to be suitable for your site.

References:

• honeypot bot report
• brute force URL lists

The Pixel 4 and Pixel 5 have multi-frequency GPS L1 and L5 bands for substantially increased navigation accuracy, as well as increased usefulness in citizen science GNSS projects. Dual frequency GNSS receivers enable additional types of ionospheric measurements not readily available with single frequency L1 GNSS receivers.

The Google Pixel 4 has been noted as having a key flaw–battery life too often less than 12 hours. Even disabling features such as Project Soli / Motion Sense and having the latest Android 11 did not greatly increase battery life beyond 18 hours. Short battery life was historically also quite an issue across numerous iPhone models, but is no longer such an issue.

The Pixel 5 uses a high-midrange CPU instead of top-end CPU in Pixel 4–the Pixel 5 CPU seems nearly as speedy as the Pixel 4.

The display panel itself is used for the top speaker–this restricts fidelity of the speaker, making it greatly emphasize midrange frequencies. This is fine for voice, but if you wish to listen to stereo orchestra music, you’d benefit from headphones.

The Pixel 5 does not have the “squeeze for Google Assistant” or Motion Sense.

The baseline battery life in the Pixel 5 is about 24 hours, which can be pushed to 36+ hours with battery saver–much better than Pixel 4. All in all, even if a used Pixel 4 is substantially cheaper, go for a used (or new) Pixel 5 instead.

Reference: dual frequency GNSS phone model spreadsheet