• 8 Posts
  • 1.31K Comments
Joined 2 年前
cake
Cake day: 2024年8月21日

help-circle


  • it’s a good attempt too, because i had completely forgot how to do that (mostly because we were taught something called the “chair method” for long division which tends to take up entire pages) and it reminded me of another thing: times tables.

    whet i was in school, we got these arithmetic worksheets with times tables on them once a week, (one meek it was 4×n, then 5, then 6…) and we were supposed to do them while being timed. iirc we had five minutes at the start of maths. i don’t think i have to tell you how stressful that is with no intuition as well as fine motor issues. anyway, point being, i don’t remember ever doing one for division. we went from pieces of pies, to the chair method, to short division problems. now, i’ve since learned that apparently the worksheet method isn’t a good pedagogical tool, but it still feels like we skipped a step.






  • holy shit, now that’s a post. very well written, easy to follow. nice.

    unfortunately, what you’ve described is basically what i’ve been doing, which is way more steps than i tend to need with the others. i don’t know if it exists in other places but we had an entire module in middle school on “överslagsräkning”, which basically translate to “rough calculations”. it was about using iterative methods like this to land at a plausible solution to a problem.

    unfortunately, i mostly need actual solutions. as an example i’ll tell you what i did today.

    today, i tried to refine an algorithm that, given a set of points (represented by a c array) and a “fractional index” (a positive non-integer value) can give result for a number between two defined points. i had previously done this through simple linear interpolation, but since we sample data from actual physical objects the points tend to represent a curve, and the common way to solve that is with a lagrange polynomial. so, i found an algorithm that, given a set of n + 1 points, evaluates the unique lagrangian of at most degree n that intersects all the points at the given index. i split the terms out to an (a + b) / c form and then i realised that i have no fucking idea what i’m doing.

    like yes, i can run the algorithm to see if the numbers line up, but i could never actually do the math. i’m not talking about the algebra part, i’m talking about the arithmetic. if i plug some numbers in and do the parts i can do, i end up with something like 0.23 / -7 and i don’t even know where to start. i have no idea where that would even land. so, while i can verify that my test data works, i have no way to quickly extrapolate numbers. which in turn means i can’t come up with plausible input. i’m back to using a calculator for that, which is so damn annoying.










  • the sr-71 is definitely not a scramble-able plane:

    • it leaks fuel when on the ground (it shrinks when cold) so it’s stored empty,
    • it’s as aerodynamic as a brick when subsonic so it needs an insanely long runway, and
    • it has an always-on afterburner so it burns an alarming amount of fuel.

    when they were doing surveys of iraq during desert storm they had to field a fleet of eight tanker planes over the indian ocean just so the damn thing would make it from japan to the gulf.

    Edit: oh and those are specially designed tanker planes because of course it uses JP-7 so they needed separate tanks for that and their own fuel. they also needed to be able to refuel at like 850km/h or the blackbird would just drop out of the sky.

    love that plane.