There are still many things in electrical engeiiring that are most easily done by iteration,
Make a reasonable assumption about current in a transitor circuit, calculate values based on data sheet plots, alter inital number based on result, re-run calculations again.
When the numbers calculated show only a small change from iteration to iteration you are done.
Something as simple as the current though a Light Emitting Diode with (LED) a current limiting resistor works this way.
The voltage drop of the LED changes with the current, and the change in current alters the voltage drop though the resistor.
Estimate voltage drop on LED, compute current, look up LED voltage drop at that current, use THAT drop and recompute.
One or two cycles should get you withing a few percent.
It is faster than trying to curve fit an equation to the LED current-voltage curve, even with curve fitting software like Easycurve.