• 0 Posts
  • 50 Comments
Joined 1 year ago
cake
Cake day: June 29th, 2023

help-circle














  • I thought it looked a bit like an Old English word maybe resurrected for D&D, so I initially thought something like /gεɑs/ (a bit like “gas” or “GEH-ahs”; ain’t no player actually gonna say /ɣ/ or /æɑ/ properly) or /jεɑs/ (“yasss”)

    Then I looked it up on Wiktionary. It’s from Irish “geis” with the wrong spelling apparently. Irish spelling do be silly, so all phonetic preconceptions should be checked at the door.

    Wiktionary says /ɟɛʃ/ for Irish, anglicized as /ɡɛʃ/ or /ˈɡiː.əʃ/ (gesh and GEE-ush, respectively).



  • Committee members be like “Oh, I definitely read your thesis titled “New Palladium-Catalyzed Reactions for the Manufacture of Pharmaceuticals”. So what is the band gap of thallium antimonide doped with 5% polonium in foot-pounds per mol? Why aren’t you answering? Even my undergrads know this!”


  • Man I just built a new rig last November and went with nvidia specifically to run some niche scientific computing software that only targets CUDA. It took a bit of effort to get it to play nice, but it at least runs pretty well. Unfortunately, now I’m trying to update to KDE6 and play games and boy howdy are there graphics glitches. I really wish HPC academics would ditch CUDA for GPU acceleration, and maybe ifort + mkl while they’re at it.


  • So many solver solutions that day, either Z3 or Gauss-Jordan lol. I got a little obsessed about doing it without solvers or (god forbid) manually solving the system and eventually found a relatively simple way to find the intersection with just lines and planes:

    1. Translate all hailstones and their velocities to a reference frame in which one stone is stationary at 0,0,0 (origin).
    2. Take another arbitrary hailstone (A) and cross its (rereferenced) velocity and position vectors. This gives the normal vector of a plane containing the origin and the trajectory of A, both of which the thrown stone must intersect. So, the trajectory of the thrown stone lies in that plane somewhere.
    3. Take two more arbitrary hailstones B and C and find the points and times that they intersect the plane. The thrown stone must strike B and C at those points, so those points are coordinates on the line representing the thrown stone. The velocity of the thrown stone is calculated by dividing the displacement between the two points by the difference of the time points of the intersections.
    4. Use the velocity of the thrown stone and the time and position info the intersection of B or C to determine the position of the thrown stone at t = 0
    5. Translate that position and velocity back to the original reference frame.

    It’s a suboptimal solution in that it uses 4 hailstones instead of the theoretical minimum of 3, but was a lot easier to wrap my head around. Incidentally, it is not too hard to adapt the above algorithm to not need C (i.e., to use only 3 hailstones) by using line intersections. Such a solution is not much more complicated than what I gave and still has a simple geometric interpretation, but I’ll leave that as an exercise for the reader :)