Of the various internet .+P, NTP is one I never learned about as a student, so now I'm looking at its web page [1] by its creator David L. Mills (1938-2024). I've found one video of him giving a retrospective of his extensive internet work; he talks about NTP at 34:51 [2] and later at 56:26 [3].
In [3] he mentions that one can use NTP to observe frequency deviations and use it as an early warning system for fire and AC failure. That really intrigues me. Can you actually? Has this ever been implemented?
Oscillators of all kinds are temperature dependent.
That's why the most stable ones are insulated and ovenized[1].
So an AC failure which would lead to higher room temperatures would lead to stronger or more frequent correction by the NTP client, as the local oscillator would drift more.
Not sure about the fire case though. I mean the same applies there but I'm not imaginative enough to think of a realistic scenario where NTP would be useful for averting a fire.
I knew of some experiments in this space back in the late 1980s or early 1990s - but it was specifically with DECstation hardware that had terrible clocks (not used for alerting, just "this graphs nicely against temperature".) https://groups.csail.mit.edu/ana/Publications/PubPDFs/Greg.T... (PDF) 4.2.1 does talk about explaining local clock frequency changes with office temperature changes (because they overwhelm a clock-aging model) but it doesn't have graphs so perhaps they weren't clear enough to include (or just not relevant enough to Time Surveying.)
Others have more complete answers, but the value for me of learning Prolog (in college) was being awakened to a refreshingly different way of expressing a program. Instead of saying "do this and this and this", you say "here's what it would mean for the program to be done".
Circle K in Chicago has them too. Employees are constantly needed to monitor things at checkout. If items aren't clearly separated (which is easy to do out of haste, not malice) it will under-count. The same cashiers at the same store were much faster at checkout than these machines are.
Thank you for giving the specific name ("Dynamic XFA (XML Form Architecture)") to the kind of PDF that generates the "Please wait" message. I have seen this and never understood how it arises. Chuck Geschke spins in his grave ...
Note: the improved loop in the "1. They are not exact" can easily hang.
If count > 2^24, then the ulp of f is 2, and adding 1.0f leaves f unchanged.
What's wild is that a few lines later he notes how above 2^24 numbers start “jumping” every 2. Ok, but FP are always "jumping", by their ulp, regardless of how big or small they are.
I started work on Teem [1] as a grad student 25 years ago; a coordinated set of C libraries for scientific visualization. It includes the original implementation of the NRRD file format [2]. One of my goals for this summer is to finally finish a version 2, so I try to spend a little time every day whittling down my todo list for that release. Currently fixing some things in the command-line parsing library ("hest"). Hearing about other people's long-standing projects is encouraging.
This is so cool. For your figures, how did you decide the RGB colors of the 4D colorspace? Or did you convince ACM to print your paper with special inks? :)
Definitely not the latter as the paper mentions "The digits are faintly visible in this photograph, because the camera’s color response differs from a human’s."
afaik not based on standard RGB displays. All widespread technology for digital color reproduction is based on RGB primaries, i.e. a 3D space of color, or rather a 3D submanifold of spectra inside the effectively infinite-dimensional space of spectra. It is feasible to test for color deficient vision (deficiency or absence of one or more cones, reducing color perception to a 2D or 1D space) because it is easy to sample 3D RGB space and behaviorally detect if colors that are different in 3D are conflated because in some viewer they project to the same location in their 2D or 1D "color" sub-submanifold.
But we'd need a convenient way to sample a 4D space of colors (perhaps with 4 monochromatic sources?), and thereby generate different spectra that normal trichromats see as the same color (called "metamers"), but that tetrachromats could recognize as distinct. And, how the 4D space is sampled would have to be pretty carefully optimized to generate distinct spectra that have the same response with the M (medium or "green") and L (long or "red") cones (which are actually quite similar already!) while also generating different responses for the putative tetrachromat's additional code between M and L. And that isn't possible with any conventional display device.
On the contrary, RGB displays should be excellent tools to determine if somebody has vision which differ from normal. Ask the person to adjust the color settings so that real world footage on the display looks like how they experience the real world. Then you will see if there's any divergence in color perception, since display images are direct light while real world vision is reflected light.
Whether via direct or reflected light, spectra in trichromat's eyes are still projected down to a 3D space (the responses of the S, M, L cones). What you describe would still require a standardized and reliable way to probe an extra degree of freedom in spectra that conventional RGB displays can't access. The paper shared by varunneal explains it better than I can.
If we assume that digital video/film recording will compress the spectrum to images which are composed of three colors, somewhere in the processes between the light hitting the camera and the light being emitted from a display to the viewer, that means any tetrachromatic person will notice a difference between the images and the real world.
Sure, but noticing a difference between the images and the real world also happens with us trichromats too, e.g. colors online don't match those in the real world if the illuminant isn't correctly controlled. The intrinsic difficulty of color reproduction is not the same as detecting tetrachromacy. The nuance here is in generating stimuli that reliably and specifically detect the difference between projecting from an infinite-D space of spectra down to 3D (via metamers like the "keef" and "litz" described in the paper linked above), versus projecting down to 4D.
The difference between display and real world will be at most slight to a trichromat, while it would be extraordinarily obvious to a tetrachromat.
It's not very uncommon for people to be colour blind, dichromats. If media on screens would be dichromatic while the world around me is trichromatic, I would certainly notice at once.
I suggest trying to quantify "extraordinarily", using the actual spectral response curve for the tetrachromat's fourth cone, called "Q" in the paper shared by varunneal. Most people casually equate the short (S), medium (M), and long (L) cones with blue, green, and red, with the idea that these are all as different as can be, but the M and L cones are very similar to each other, compared to S. The L, M, S curves are independent but far from orthogonal in the way you may be thinking as you say "extraordinarily". The Q curve is just another wide bump, with a peak in between that of M and L, so again, very far from being orthogonal. Whatever 4th dimension of color perception is accessed by the Q curve, it is a relatively cramped dimension, so reliably detecting perception along it requires some carefully designed stimuli.
Like others[1] I was saddened that Mac's Preview program stopped opening .ps/.eps files with the release of Ventura in late 2022. I never understood exactly why; I guess security issues around the PostScript interpreter. But that made it lot less convenient to hack around in .ps files. Ghostscript's interactive display program(s?) never seemed as convenient as Preview.
Still, this book is awesome and I've been inspired by it for awhile. I used to love whipping up diagrams and simple vector art in .ps/.eps files. In a fit of procrastination in ~2006 I created a minimalist horizontal rule for an IEEE conference submission, and that diamondrule.eps[2] has now become the standard. I would say that EPS is still more convenient than SVG as a format to contain, in one self-contained file, raster graphics with overlaid vector graphics.
I learned about the Schwebebahn from this[1] YT video (from The Tim Traveller), which goes into the history of why it made sense to build a suspended rail at this particular place and time. A more recent video [2] gives a much more detailed history.
[1] https://www.eecis.udel.edu/~mills/ntp.html
[2] https://youtu.be/08jBmCvxkv4?si=WXJCV_v0qlZQK3m4&t=2092
[3] https://youtu.be/08jBmCvxkv4?si=K80ThtYZWcOAxUga&t=3386
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