Scientific Computing

NOTE: Matlab R2024b and newer no longer use the internal Help browser for doc, instead referring “doc” commands to the system web browser.

After opening the Matlab Help Browser, Matlab might use 100% of one CPU core at about 25% duty cycle. Even after closing just the Help Browser while keeping Matlab itself open, this problem may persist.

Workaround: a one-time persistent setting.

Type in Matlab:

com.mathworks.mlwidgets.html.HtmlComponentFactory.setDefaultType('HTMLRENDERER');

Restart Matlab, reopen and close Matlab Help Browser. The CPU is no longer hanging at 100% after closing the Help Browser. However, this simpler Help Browser is not as graphically nice as the default Help Browser. Clickable links won’t work in the help files.

Undo workaround: revert back to the default Help Browser with this one-time persistent setting. Type in Matlab:

com.mathworks.mlwidgets.html.HtmlComponentFactory.setDefaultType('HTMLPANEL');

then restart Matlab.

Disable the Beaglebone Black flashing LEDs temporarily or permanently:

Persistently (permanently) disable: add to /etc/rc.local

echo none > /sys/class/leds/beaglebone\:green\:usr0/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr1/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr2/trigger
echo none > /sys/class/leds/beaglebone\:green\:usr3/trigger

Reference

Temporary disable (till reboot):

echo none > /sys/class/leds/beaglebone:green:usr0/trigger

Alternative: apt install astrometry.net

Install GCX

apt install gcx

GSC ACT catalog

there are a lot of directories with lots of ~50KB files, so it will take a while even with a very fast internet connection.

mkdir ~/gsc-act
cd ~/gsc-act

wget -r -nH --cut-dirs=5 ftp://cdsarc.u-strasbg.fr/pub/cats/I/255/GSC_ACT/

set File → File and Device Options/GSC to /home/username/gsc-act

username

your linux login

Tycho2 star catalog

mkdir ~/tycho2 && cd ~/tycho2

wget -r -nH --cut-dirs=5 ftp://cdsarc.u-strasbg.fr/pub/cats/I/259/

Once you see that they’ve downloaded correctly, do:

zcat tyc2.dat.??.gz > tycho2.dat

set File → File and Device Options/Tycho2 to /home/username/tycho2

username

your linux login

The “Who’s Afraid of Peer Review” article DOI: 10.1126/science.342.6154.60 notes that:

…Ocorrafoo Cobange does not exist, nor does the Wassee Institute of Medicine…submitted 304 versions of the wonder drug paper to open-access journals. More than half of the journals accepted the paper, failing to notice its fatal flaws…the data from this sting operation reveal the contours of an emerging Wild West… …acceptance was the norm, not the exception…

Counter-argument from Curt Rice in the Guardian

Some think the Earth is spherical, others that it is flat and drum-shaped. For evidence they bring the fact that, as the sun rises and sets, the part concealed by the Earth shows a straight and not a curved edge, whereas if the Earth were spherical the line of section would have to be circular . . . . . . but in eclipses of the moon the outline is always curved: and, since it is the interposition of the Earth that makes the eclipse, the form of this line will be caused by the form of the Earth’s surface, which is therefore spherical.

Aristotle. “On the Heavens”. Written 350 B.C.E.

Quoted in: Kabanikhin, Sergey I. Inverse and Ill-Posed problems

apt install octave-info

fixes the error message about missing files when using the doc command in GNU Octave.

Imaging from sparse measurements: Y. Fang, M. Cheney and S. Roecker

On NUFFT-based gridding for non-Cartesian MRI: Jeffrey A. Fessler

if you get a winetricks error like:

wine cmd.exe /c echo '%ProgramFiles%' returned a string containing the word 'unknown', as if a voice had cried out in terror, and was suddenly silenced.

Fix: backup existing system.reg file by typing in Terminal:

cp ~/.wine/system.reg ~/.wine/system.reg.bak

Use text editor and “replace all”

C:\\windows\\system32\\unknown

with

C:\\Program Files

The circa 1999 intercoms at 900 MHz from Radio Shack (model 43-3102, FCC ID AAO4303102) are long range, reliable intercoms operating with wideband FM analog modulation. Several hundred feet range between intercoms is possible with 2 milliwatts RF output and wideband 75 kHz FM modulation yielding audio frequency Response (–3 dB Bandwidth) of 300 Hz - 10 kHz These intercoms are specified at -109 dBm 20 dB SINAD sensitivity (very good) and up to 200 feet range per the manual. In practice they might reach 500 feet range with line of sight (placed near windows, not blocked by metal structures).

Intercom squelch is set a bit too tight from the factory, which reduces range. The CTCSS/PL squelch system (10 kHz deviation) uses several of the same subaudible tone frequencies as standard two-way radios. The user can select between 2³ = 8 CTCSS tones and 2² = 4 channels. The intercom will only open the squelch if matching correct channel and subtone are detected with adequate RF signal strength. Correctly lowering the squelch threshold allows weaker RF signals to be heard.

Squelch adjustment tradeoffs

For this intercom, the squelch potentiometer makes the squelch “tighter” with counterclockwise turning and “looser” with clockwise turning. On this intercom, when the squelch is open (but with no/incorrect CTCSS) the middle RX LED will flicker once per second. When the squelch is set just tight enough to stop the RX LED from flashing with no incoming RF signal, the RF RX sensitivity is maximum (maximum range).

If the squelch threshold is set too low, there can be occasional bursts of static (CTCSS false decode). Also, for battery operated intercoms, the battery consumption will be higher if the squelch is always open as it’s trying to find the CTCSS tone constantly, putting the receiver into full power drain.

For integer xlabel and ylabel (e.g. 362093) put the following line after you set xlabel or ylabel:

set(gca, YTickLabel=sprintf('%7d|', get(gca,'YTick')))

%7d|

up to 7 integer digits on y-axis.

Matlab default behavior, which Mathworks says is currently not changeable, is to put exponential format into xlabel and ylabel for large numbers–even integers.