• linearchaos@lemmy.world
    link
    fedilink
    English
    arrow-up
    0
    ·
    2 months ago

    I could never remember the formula to calculate compound interest.

    But I had no trouble writing a for loop.

    • BluesF@lemmy.world
      link
      fedilink
      English
      arrow-up
      0
      ·
      2 months ago

      What always annoyed me was having to draw charts by hand. Just let me put the data in a computer for god’s sake, the rest of the working is there… I did actually write a python function for one of my assignments which was fine, but they told me not to do it for the exam.

      • linearchaos@lemmy.world
        link
        fedilink
        English
        arrow-up
        0
        ·
        2 months ago

        I would just rebuild something in my head like this every time.

        While i < n; k=k+(k*r); i++;

        You’d think I could remember k(1+r)^n but when you posted, it looked as alien as it felt decades ago.

        • VintageGenious@sh.itjust.works
          link
          fedilink
          English
          arrow-up
          0
          ·
          2 months ago

          The use of for makes sense.

          k=0; for (i=0; i<n; i++) k=k+f(i); is the same as k=\sum_{i=0}^{n-1} f(i)

          and

          k=1; for (i=0; i<n; i++) k=k*f(i); is the same as k=\prod_{i=0}^{n-1} f(i)

          In our case, f(i)=1+r and k=1; for (i=0; i<n; i++) k*(1+r); is the same as k=\prod_{i=0}^{n-1} (1+r) = (1+r)^n

          All of that just to say that exponentiation is an iteration of multiplication, the same way that multiplication is an iteration of addition