These enhancements are needed for drawing figures like 5.38 and 5.39.
Rbs is load resistance of driver stage, RL2 in fig 5.46.
ibs is current in load resistor, but not used in any program.
To draw a load line in fig 5.39, you need another function "trans.bs",
which is not published yet.
Without this parameter, result is not so different from true value.
Parallel push-pull and bootstrap are very complicated and not totally exploited yet by me.
I'm now rewriting these sections, so I will then explain how to draw these load lines.