Scientific Computing

P.C. Hansen 1998. Rank-Deficient and Discrete Ill-Posed Problems. SIAM.

Data drive write caching can lead to data loss upon unplugging an external flash drive or hard drive. Inexpensive USB flash drives may write data slowly. Operating systems use RAM to cache write data, making the copy/write operation appear done while the final data writing is actually still underway. If the drive is removed before the writing is done, that file or even the whole disk can become corrupted and unreadable.

For example, a drive writing at 10 MByte / second for a 1 GByte file could take 1000 / 10 = 100 seconds, despite the file copy operation appearing done in less than 10 seconds.

On macOS or Linux, verify writing to a flash drive is completed with sync and then click the Eject icon next to the drive’s name in Finder or File Manager.

Monitor macOS or Linux file write progress with iotop.

For Windows, use the Safely Remove Hardware icon in the system tray. Monitor Windows file write progress with Task Manager or Process Explorer.

Large pixel-count or frame-count AVIs can be converted frame-by-frame to PNG. One can then use Irfanview or other common image browser to flick back and forth between movie frames.

The conversion uses ImageMagick, which calls FFmpeg.

magick -verbose CMOSvideoshorter_halfspeed.avi -type Grayscale CMOSvideo_%03d.png

Change the baud rate of the Kenwood TS-2000 over the RS-232 serial COM port locally or remotely. Faster rates are less reliable but enable quick parameter changes. 57600 has been reliable for me with the Kenwood TS-2000 for many years, but if you have high stakes operation or a noisy environment, in general slower serial speeds are more robust.

Local baud rate change

1. menu 56
2. select baud rate. Hamlib/rigctl recommends using the highest possible baud rate i.e. 57600 baud.
3. power cycle the radio.

Remote baud rate change

1. CAT EX menu item 56.

2. Read the current baud rate by sending

    EX0560000;
   

3. The radio will answer back

    EX05600004;
   

   which implies 57600 baud since the last digit is 4.

The last digit to baud is:

0: 4800
1: 9600
2: 19200
3: 38400
4: 57600

To set baud rate remotely, send the corresponding command. E.g. to set 57600 send:

EX05600004;

and turn off the TS-2000 by sending

PS0;

Now disconnect, and reconnect at the new baud rate (here, 57600) and turn the radio on by sending:

PS1;

Note: Lost communication with the TS-2000 requires a site visit. Be prepared.

collection of Bash scripts for extensive command line control of radios and rotors via Hamlib rigctld and rotctld

NOTE: if using GPredict with Hamlib, do not use -v verbose options, since the extra text output will confuse Gpredict.

Lenovo offers a 2880 x 1620 pixel T540p laptop that is on par with the MacBook Pro Retina 2880 x 1800.

There are other points to consider such as weight and price. The Lenovo 540p is nice for Linux with a Haswell quad-core CPU and user-upgradable RAM (up to 16GB RAM), HDD and DVD.

The Lenovo T540p is less than half the price $1300 vs. less-well equipped Apple MacBook Pro Retina at $2600.

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