141 pointsby E-Reverance6 hours ago9 comments
  • helterskelter4 hours ago
    Logs are awesome. I started a math textbook from the 1920's a while ago, and all the calculations relied on tabulated logs, where you would convert the number to a log in a table to reduce the operation's degree, then convert back to the ordinary representation. This would reduce operations like finding cubed roots to division, would could be converted to log-log to be further reduced to subtraction before you would restore to ordinary notation. It feels like you're using a magic wormhole or something when you're doing this stuff by hand, it's really neat.
    • badlibrarian4 hours ago
      The physical version of that magic wormhole is called a slide rule.
      • eru26 minutes ago
        Another neat application, if a bit simplistic, are these mechanical paper computer that let you figure out your body-mass-index. They are basically two disks with logarithmic scales on them that you rotate relative to each other. Like a slide-rule, but circular. I think you can find them under the name 'BMI wheel'.
    • all234 minutes ago
      Got a PDF? I love old books like this.
    • eager_learner4 hours ago
      care to share the name of the said book?
      • helterskelter4 hours ago
        Trigonometry for Navigating Officers by WP Winter

        https://www.google.com/books/edition/Trigonometry_for_Naviga...

        I found this book because I was a little rusty on my trig and most celestial navigation texts will just throw the PZX equation (and others) at you without breaking down what's actually being done with it on a mathematical level...it's just kind of treated like a magical black box without any discussion, and I'd rather have a complete understanding of what I'm doing and why. Having an application-specific approach also makes it a lot easier to learn.

        I'm using it with Norie's Nautical Tables, which has the log tables and a whole lot else:

        https://bluewaterweb.com/product/nories-nautical-tables-2025...

        I'm sure there are plenty of free PDF's of log tables you can find though.

        (I believe they used log tables on boats primarily because it's easier to use than a slide rule when everything is constantly rocking back and forth.)

  • badlibrarian5 hours ago
    This essay needs a type system. Every time it says “log” it should say: log of what, into what?

    It’s like audio where people say "dB" as if it answers the next question. Relative to what, measured how, and weighted for whom?

    Author should brush up on https://en.wikipedia.org/wiki/Lie_theory

    • rq12 hours ago
      The important properties of the logarithm are structural: we usually do not care about units or bases, except when carrying out an actual numerical computation.

      As developed in the article, informally, but somewhat sufficiently, the change of base formula shows that the choice of base is largely irrelevant: different bases give equivalent logarithms up to a constant factor.

      The Taylor expansion of exp gives a more intrinsic and general definition of the exponential function. This allows exp to be generalised structurally to many algebraic settings, provided the relevant convergence conditions are met: for example, the complex exponential and its many possible logs, the matrix exponential, and so on…

      • eru25 minutes ago
        > The important properties of the logarithm are structural: we usually do not care about units or bases, except when carrying out an actual numerical computation.

        Units are important as a sort-of type system, even at the conceptual level.

        You are right that bases are not as important conceptually.

    • jfengelan hour ago
      I still don't understand why audio dB are negative. That's relative to what? What happens at 0dB?
      • eru25 minutes ago
        Well, the brightness of celestial objects is also sometimes negative:

        > The apparent magnitude of known objects can range from −26.832 for our Sun to about +31.5 for objects in deep space imaged by the Hubble Space Telescope.[3]

        See https://en.wikipedia.org/wiki/Apparent_magnitude

      • deepspacean hour ago
        0db is usually defined as the loudest sound that the audio system can produce. Hence, everything else must be negative.
      • kevin_thibedeauan hour ago
        That is dB full scale where 0 is an absolute ceiling and you can deduct from there.
    • jmyeet5 hours ago
      The first section details how the author thinks of "log N" with no base as an abstract object rather than a number. Or what are you referring to?
      • badlibrarian5 hours ago
        The first section is the good part.

        The later reuse of “log” across valuations, dimension, vector fields, orders of vanishing is not so good. Those may be related ideas, but each needs a type signature: from what, to what, and preserving which operation?

        • exmadscientist3 hours ago
          Or, to say a little more explicitly what you're getting at: when you take a logarithm of some quantity, log x, x absolutely must be unitless. There's no way whatsoever to take a logarithm of something with a unit attached. (This is an important and useful dimensional analysis check in formulas and long calculations!)

          So what do you do in practice? You have to normalize: you don't calculate log x, but instead log x/U for some scaling unit U. It's typical for U to be something like 1 mV or 1 W in electrical engineering, for example. This is completely legitimate, but it does mean that the thing that comes out needs a corresponding unit attached to it: dBmV, dBW, et cetera.

          And it's really kind of important to be careful about that.

  • aesthesia2 hours ago
    I think what's going on with the complex logarithm is basically the same as the logarithm that outputs the set of all possible bases for a vector space. The complex logarithm produces a Z-torsor, and the basis logarithm produces a GL(V)-torsor. There's probably some way to represent a choice of branch cut as a part of the choice of the base of the complex logarithm, and similarly the choice of a specific basis as part of the choice of base of the vector space base logarithm.
  • kfsean hour ago
    All this would be way more interesting if it actually helped to demonstrate a novel mathematical fact. Right now it's more like notational play.
    • sixo38 minutes ago
      I read this kind of essay as a certain part of the arc by which new thoughts are formed: an act of large-scale pattern matching, laying out a bunch of cases which resemble each other, searching for the essential basis of the resemblance.

      To post such a pattern allows the thought process to become distributed. Perhaps someone else will see the insight.

  • anArbitraryOnean hour ago
    I can't believe he called normal logarithms 'based'
  • saulpw2 hours ago
    This sentiment (not necessarily the content) is what I'm striving to communicate with Mag World[0] (website and podcast so far).

    [0] magworld.pw

  • amelius5 hours ago
    Does this answer the question of why we see hyperoperations until exponentiation in physics, but not higher?
    • AnotherGoodName4 hours ago
      I think that's more about integrations/differentials not producing them (generally speaking). Physics likes to deal with integrals and differentiation as you calculate change over time or over spatial dimensions.

      Eg. the integral of x^10 is x^11 / 11 + c. No hyper-operation appears and it's just another exponential (with a division).

      The integral of log(x) is xlog(x) - x + c. So still basically just a logarithm

      Even the integral of 2^x is just 2^x / log(2). Still basically the same thing.

      There's no easy way to pull a hyper-operation out.

  • jongjong5 hours ago
    That's a lot of ways to think about logarithms.

    Logarithms are laughably simple once you've fully internalized the meaning of the log function; it simply answers the question:

    "To what power must I raise the base to get the argument?"

    This is why the output tapers out as you increase the argument; because even if you increase the argument exponentially, you only need a fixed increment in the power to reach that number... So if you increase the argument only by a fixed amount (linearly) instead of exponentially, then it makes sense that the output will grow sub-linearly.

    I remember when I was doing algebra with logs many years ago at school, I was applying rules to remove the log from one side of the equation.

    Then when I got to uni, I had to revise the rules but it was kind of silly of me because those rules can be trivially derived if you just think about what the log function means. Turns out I had been solving equations with logs throughout school without understanding what they even meant... It's only at university that I actually bothered to learn them.

    Actually TBH. I didn't even fully understand powers for some time even though I was doing calculus with them at school. I only fully understood powers once I properly internalized the concept of k-ary trees as a proxy.

    It's one thing to be able to apply something, another to understand it. And I think to innovate with something, as a tool, it's not enough to be able to apply it. You must understand it.

  • yaccb35 hours ago
    Look, the whole thing actually makes sense and the core idea is pretty cool because it's true that a lot of stuff in math looks identical. But in my opinion this is way too much of a macro-level overgeneralization and you risk throwing everything into the same pot, which ends up diluting the actual point of things.I mean, if you take a hammer and a meat mallet, at the end of the day they're both chunks of metal used to hit stuff, but if you bunch them together without making any distinction, you lose track of why you use one to drive nails into a wall and the other to prep cutlets.Saying everything is just one big logarithm is a nice mental exercise, but I feel like it flattens out the differences too much and makes you lose the practical utility of the individual math tools, which are meant to solve completely different problems.