Author Archives: mea

Rockets Shake And Rattle, So SpaceX Rolls Homegrown CFD

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Lichtl says that people have tried to use wavelet compression before, and these particular simulations are based on work done by Jonathan Regele, a professor at the department of aerospace engineering at Iowa State University.

“The difference is that without GPU acceleration, and without the architecture and the techniques that we just described, it takes months on thousands of cores to run even the simplest of simulations. It is a very interesting approach but it doesn’t have industrial application without the hardware and the correct algorithms behind it. What the GPUs are doing here is enabling tremendous acceleration.

via Rockets Shake And Rattle, So SpaceX Rolls Homegrown CFD.

To be more precise, if you get the temperature wrong in the simulation by a little, you get the kinetic energy of the gas wrong by a lot because there is an exponential relationship there.  If you get the pressure or viscosity of the fluid wrong by a little bit, you will see different effects in the nozzle than will happen in the real motor.

New Homeowner Has To Sell House Because Of Comcast’s Incompetence, Lack Of Competition

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According to the latest Broadband Progress Report from the FCC, 4% of all Americans — and only 2% of people in Washington state — lack access to even the most basic non-mobile broadband service. But Seth’s story makes us wonder how many consumers are being counted as having access to these services when in fact the service providers refuse to make them available?

That’s why it’s in the best interest of Comcast, CenturyLink and others to assume an address is serviceable just because it falls within a certain ZIP code or municipal boundary — because it gives the illusion that they are providing service to more customers.

via New Homeowner Has To Sell House Because Of Comcast’s Incompetence, Lack Of Competition – Consumerist.

The FTC’s internal memo on Google teaches companies a terrible lesson

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FTC staffers spent enormous time pouring through Google’s business practices and documents as well as interviewing executives and rivals. They came to the conclusion that Google was acting in anti-competitive ways, such as restricting advertisers’ from working with rival search engines. But commissioners balked at the prospect of a lengthy and protracted legal fight, former FTC officials said.

via The FTC’s internal memo on Google teaches companies a terrible lesson – The Washington Post.

DRIVE IT YOURSELF: USB CAR

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What we are going to do is a basic variant of a process generally known as reverse engineering. You start examining the device with common tools (USB is quite descriptive itself). Then you capture the data that the device exchanges with its existing (Windows) driver, and try to guess what it means. This is the toughest part, and you’ll need some experience and a bit of luck to reverse engineer a non-trivial protocol.

via DRIVE IT YOURSELF: USB CAR | Linux Voice.

Windows 10 to make the Secure Boot alt-OS lock out a reality

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At its WinHEC hardware conference in Shenzhen, China, Microsoft talked about the hardware requirements for Windows 10. The precise final specs are not available yet, so all this is somewhat subject to change, but right now, Microsoft says that the switch to allow Secure Boot to be turned off is now optional. Hardware can be Designed for Windows 10 and can offer no way to opt out of the Secure Boot lock down.

via Windows 10 to make the Secure Boot alt-OS lock out a reality | Ars Technica.

Universal Music Hijacks YouTube Videos of Indie Artist

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Apparently UMG has the rights to an audiobook that uses Lynne’s music track “Kingdom of the Persians” as background music. This isn’t a problem, as his music can be freely used as long as the license fees are paid.

However, UMG have entered the audiobook in YouTube’s Content-ID system, and as a result they’ve hijacked the ads on the original video. Making matters even worse, UMG also rejected Lynne’s dispute through YouTube after he explained the situation.

via Universal Music Hijacks YouTube Videos of Indie Artist | TorrentFreak.

ffmpeg – encode video in reverse?

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Dump all video frames

$ ffmpeg -i input.mkv -an -qscale 1 %06d.jpg

Cat video frames in reverse order to FFmpeg as input
$ cat $(ls -t *jpg) | ffmpeg -f image2pipe -vcodec mjpeg -r 25 -i - -i backwards.wav
-vcodec libx264 -vpre slow -crf 20 -threads 0 -acodec flac output.mkv

via ffmpeg – encode video in reverse? – Stack Overflow.

The above ffmpeg command examples turned out to be very useful.  Previously I had to do this manually in Avidemux.

The output of my IP camera is VGA 640×480 and I needed to slice that up into a  10×10 array of little areas  (100 jpeg files) using the following:

convert input.jpg -crop 64x48  +repage  +adjoin  myoutputfile_%02d.jpg

Motion detect reveals a lot of false positives which must be filtered out manually.  In order to automate this I  compare time n to time n+1 in only a couple of the 100 little jpegs separated in the above command.   So far I’m using this:

compare -metric MAE time_n_number.jpg time_n+1_number.jpg  null: 2>&1

A changed portion of the jpeg will generate a high number which can be compared to a threshold in a script allowing me to eliminate most all false positive motion detects.

More detailed explanation for the Image compare commands in the ImageMagick package can be found here:

ImageMagick v6 Examples –Image Comparing

Therefore my entire process consists of separating the video into jpegs, finding changes in areas where there shouldn’t be changes and if not reassembling the jpegs back into a video file again all done automatically via bash scripting.

There probably are more elegant solutions but this works for now.

Counting Legal Positions in Go

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The computation uses dynamic programming to count the number of paths through a graph consisting of 18^2=324 layers with up to 81 billion nodes each. Each node corresponds to a set of partial board (e.g. the top 7 rows plus 6 points on the 8th row) positions that are equivalent in their set of valid completions. Our paper explains the algorithm in detail, and also explains how the resulting exact counts allow derivation of the approximation formula

L(m,n) ~ 0.850639925845714538 * 0.96553505933837387^{m+n} * 2.97573419204335724938^{m*n}

which gives us the approximate number of legal positions on a standard board size

L(19,19) ~ 2.08168199381982*10^170

via Counting Legal Positions in Go.

Thanks to the Chinese Remainder Theorem, the work of computing L(19,19) can be split up into 9 jobs that each compute 64 bits of the 566-bit result. Allowing for some redundancy, we need from 10 to 13 servers, each with at least 8 cores, 512GB RAM, and ample disk space (10-15TB), running for about 5-9 months.

The SSD Endurance Experiment: They’re all dead

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The SSD Endurance Experiment represents the longest test TR has ever conducted. It’s been a lot of work, but the results have also been gratifying. Over the past 18 months, we’ve watched modern SSDs easily write far more data than most consumers will ever need. Errors didn’t strike the Samsung 840 Series until after 300TB of writes, and it took over 700TB to induce the first failures. The fact that the 840 Pro exceeded 2.4PB is nothing short of amazing, even if that achievement is also kind of academic.

via The SSD Endurance Experiment: They’re all dead – The Tech Report – Page 4.

If you write a lot of data, keep an eye out for warning messages, because SSDs don’t always fail gracefully.