emergence work:

260619:

mass had to grow with age, but then slow down. tried logarithmic growth, but that wasn’t proper (as growth needs to have a ceiling). could have used constrain, but that’s unnecessary computation.

found this: https://math.stackexchange.com/questions/2821035/exponential-something-what-is-the-name-of-that-asymptotic-exponential-functi (thanks to jagi).

equation:

$$f(x)=a.(1-e^{-x/b})$$

which can be implemented like so:

    const a = 100; //max. 
    const b = 50; //how quickly max is achieved.
    const base = 50; //to ensure base of graph doesn't shift.
 
    y = base + a * (1 - Math.exp(-(x - base) / b));

plotted like this: