Scientific Computing

Concurrency is built into Python via asyncio. AsyncIO generators are implemented with yield much like synchronous generators. async for also simplifies expression of asynchronous for loops.

As in Julia, the expression of asynchronous structures in Python does not implement concurrent execution. Concurrent execution in Python is governed by collections of tasks or futures such as asyncio.gather and initiated by a runner such as asyncio.run.

Debugging asyncio code is facilitated by introspection built into Python.

asyncio.subprocess

AsyncIO subprocess may need specific asyncio loop configuration. The options needed are not the same for every project, depending on the asynchronous functions used.

Example date_coro.py uses AsyncIO subprocess.

asyncio.open_connection

For networking apps asyncio.open_connection allows massive amounts of connection, as shown in findssh.

Matlab can call user Python modules via the Matlab external language interface. For concurrent Python modules using asyncio, you may need to create a shim function to allow Matlab to call the Python module. Anaconda Python works fine from Matlab.

Configure Matlab for Python: Matlab is designed to work with specific Python versions for each Matlab version. Matlab will not specifically tell you when you’re using an incompatible Python version, but you may get unstable operation or errors. pyenv Python environment manager configures the Python interface.

The Python executable is found from Terminal / Command Prompt:

python -c "import sys; print(sys.executable)"

For Windows, it may be like C:/Miniconda3/python.exe and for macOS / Linux it may be like ~/Miniconda3/python.

This Matlab command is persistent–Matlab remembers this Python choice even after restarting Matlab.

pyenv(Version='C:/Miniconda3/python.exe')

Verify Matlab → Python config by typing pyenv from within Matlab.

Troubleshooting

If a non-supported Python version is used, upon the pyenv() command Matlab may show a warning like:

Warning: Python version 3.xx is not supported. See this topic.

In that case, some Python operations may work, but others may not. An example test that may fail is:

py.tuple([1,1]);

PythonError ImportError: PyCapsule_Import could not import module "libmwbuffer"'

Numpy

If only Python standard library modules work, and even commonly used modules like Numpy will not work, errors may occur from Matlab like:

py.numpy.arange(1)

Unable to resolve the name py.numpy.arange

Try diagnosing the issue from Matlab like:

pyenv

help('py.numpy')

Verify the desired Python install is being used, and that there isn’t an error as below. If such an error occurs, check the PATH as seen by Matlab by:

getenv('PATH')

If the Python directories are missing, this may be why user modules are not importable in Python. These paths can be added to Matlab. On Windows, the necessary path is like ~/Miniconda3/Library/bin, the directory with lots of *.{so,dylib,dll} files and the fix is like:

setenv('PATH', fullfile(getenv("USERPROFILE"), "Miniconda3/Library/bin") + pathsep, getenv('PATH'))

The install path on non-Windows OS is like ~/miniconda3/lib.

This command can be issued after a Python command was attempted, it’s not necessary to restart Matlab. Note that this needs to be in PATH, since PYTHONPATH does not help in this case. This change does not persist across Matlab sessions. If it works for you, put it in the ~/Documents/MATLAB/startup.m file to have it reload each time Matlab is started.

This Numpy problem is fixed by the procedure above:

problem in numpy - ImportError:

IMPORTANT: PLEASE READ THIS FOR ADVICE ON HOW TO SOLVE THIS ISSUE!

Importing the numpy c-extensions failed.
- Try uninstalling and reinstalling numpy.
- If you have already done that, then:
  1. Check that you expected to use Python3.7 from "C:/Miniconda3/python.exe",
     and that you have no directories in your PATH or PYTHONPATH that can
     interfere with the Python and numpy version "1.17.4" you're trying to use.
  2. If (1) looks fine, you can open a new issue at
     https://github.com/numpy/numpy/issues.  Please include details on:
     - how you installed Python
     - how you installed numpy
     - your operating system
     - whether or not you have multiple versions of Python installed
     - if you built from source, your compiler versions and ideally a build log

- If you're working with a numpy git repository, try `git clean -xdf`
  (removes all files not under version control) and rebuild numpy.

Note: this error has many possible causes, so please don't comment on
an existing issue about this - open a new one instead.

Original error was: DLL load failed: The specified module could not be found.

• Python module import is implicit in the Matlab → Python module function call. There is no need to import numpy etc. from Matlab
• Python executable choice persists across Matlab sessions–Matlab “remembers” even after you restart Matlab or reboot the computer.
• editing imported Python module code requires restarting Matlab to take effect.

Starting with Windows 25H2, WMIC.exe (Windows Management Instrumentation Command-line) has been removed from the operating system. Microsoft recommends using PowerShell cmdlets for managing and querying system information instead. There is a migration guide available to help users transition from WMIC to PowerShell cmdlets that invoke WMI.

There are a lot of .bat batch scripts and .ps1 PowerShell scripts that use WMIC.exe, but they can be updated to use PowerShell cmdlets instead.

Get Windows - or any operating system with PowerShell - uptime by cmdlet Get-Uptime

Get-Uptime

To get system uptime from Python without forking a new process, see the uptime Python module.

Caution: in Java, ManagementFactory.getRuntimeMXBean().getUptime() returns uptime of the JVM process, not the OS.

Build systems like CMake and Meson have specific syntax and variables to manage shared library creation and linking. By default, CMake builds static libraries, but this can be changed by setting the BUILD_SHARED_LIBS variable to ON or by setting the SHARED type option of the add_library() command.

To use C, C++, Fortran, etc. library binaries from Python, shared libraries are required to load the compiled code at runtime in Python. Of course, the Python code must be configured to match the symbols in the shared library.

Meson builds shared libraries by default, but this can be changed by setting the default_library option to static in project() or by the shared_library() function.

Strip most EXIF and IPTC headers from image:

exiftool -all= -photoshop:all= myphoto.jpg

A copy of the image _original is kept. The image is not recompressed so image quality is not affected.

Compare the metadata present on old and cleaned images using ImageMagick:

magick identify -verbose myphoto.jpg

magick identify -verbose myphoto.jpg_original

Not all headers can be removed, but it usually works.

Install Exiftool:

• Linux: apt install libimage-exiftool-perl
• macOS: brew install exiftool
• Windows installer

Hugo content Markdown files cannot use Hugo variables directly. The way to access variables (including site parameters, data sources, and front matter) from content Markdown files is to use Hugo shortcodes or to use a custom template for those content pages. However, areas inside code fences cannot use shortcodes. What I wanted to do was make examples of code inside code fences used on several pages on my site update with a version number. However, I don’t currently see a feasible way to do this with Hugo that wouldn’t be overly specific to the particular set of examples. It’s OK, I wanted to note this limitation I ran into. An alternative is to use find/replace across files like “sed” or the VSCode GUI.

To run Linux programs on a Windows computer, normally Windows Subsystem from Linux (built into Windows by Microsoft) is generally the best / most performant way to run most Linux programs, especially programs relevant to data processing and geospace science in general.

The WSL Install Guide notes from Windows Terminal:

wsl --install

That will install Ubuntu. After a few minutes the Ubuntu WSL install will be complete. From Windows terminal type:

wsl

to start Ubuntu.

From there type

sudo apt install gnss-sdr

That installs numerous packages needed to run GNSS-SDR.

Then proceed to the first-run examples.

When building GNSS-SDR and examples, don’t worry about CMake warnings about missing packages, as long as the project builds.

The macOS network interface priority order determines which network interface (like WiFi, Ethernet, etc.) the system uses first when multiple interfaces are available. Set this priority order through the System Preferences or via the command line:

List all network services in priority order:

networksetup -listallnetworkservices

Set the network interface priority order with:

networksetup -ordernetworkservices "Service1" "Service2" ...

Replace "Service1", "Service2", etc., with the actual network service names.

Regarding WiFi SSID priority, macOS automatically scores based on several factors, including the user manually selecting a WiFi network.

The USA and Canada permitted FM frequency modulation, optionally with CTCSS and DCS, on 27 MHz CB radio in September 2021. This allows FM operation on the same 40 channels as AM CB radio at 4 watts maximum transmit power. Observations by USA users including the author is that FM is heard mostly in the range of CB radio channels 23 to 31. Any CB radio channel can be used with FM mode, the same as AM or SSB modes. A rise in FM activity over time is also expected on the President P channels that are preprogrammed FM standard CB radio channels with CTCSS / DCS squelch.