simple math transformation with mappings

[LasseNT]

It would be great to be able to setup mappings as simple equations

a = (b +c) * 3

a -= 2 * b + 5

or maybe:
a.map(b, scale=-10, offset=4)

The pain point is now primarily that creating variables in scopes for simply inverting the sign of another variable before mapping is quite cumbersome.

Supporting units and operations between units will be simpler if scaling and offset could be added to mappings.