Seems to me that you would instead simulate the circuit
and take the results of a .measure statement (set) -
if you want to calculate and plot from "inputs" then a
tool like Excel or Matlab seems more suitable.
I've used SPICE variants that had robust command-line
interfaces and could do stuff like this (loop, calc, stuff
to a vector, endloop, plot vector) but not sure whether
this is really practical in a "standard" SPICE with a
divorced waveform viewer, etc.