There probably is but I don't use Hspice so I don't know the syntax. You could add an E source between the two nodes and ground the negative output node of the E source.
What do you mean with "curve" ? The voltage difference between both nodes?
In this case, you let calculate all node voltages and path currents (dc, ac or tran) and, then, let display V(x)-V.
This is what I meant - assuming A and B are your two voltages, add E and plot the output. It would be easier to simply plot the difference though, if someone can tell you how (my simulator has difefrential probes anyway without having to type in equations).
so you are running tran analysis, you can do it in *.sp file for this, e.g. you can to get the voltage difference (vdiff) between node a and node b versus time by the following:
.probe vdiff=par('v(a)-v(b)')
but you said x-axis is time!
ok, it seems it's difficult to do it in *.sp file except for DC analysis, anyway, i think you can process it by waveform tool.