Isn't it fairly clear:

**Code:**// Implement switch with effective series resistence of 1 Ohm
if (($abstime > tstop – aperture) && ($abstime <= tstop))
I(hold) <+ V(hold) – V(Pin, Nin);
else
I(hold) <+ 1.0e–12 * V(hold);
// Implement capacitor with an effective capacitance of tc
I(hold) <+ tc * ddt(V(hold));
// Buffer output
V(Pout, Nout) <+ V(hold);

The first bit is a switch, which is either a 1 ohm series resistor,

or a leakage resistance of 1 teraohm to ground.

The second is the equation for a capacitor.

And finally V(hold) is used.

With Verilog-A you can write the relationship between currents and voltages - you don't always have to formulate the equation so that the voltage is assigned to.

For example, a resistor can be defined as:

**Code:**I(plus,minus) <+ V(plus,minus)/R;

just as well as:

**Code:**V(plus,minus) <+ I(plus,minus)*R;

both forms are effectively equivalent.

So do you understand now? If not, can you elaborate on what it is you don't understand?

Regards,

Andrew.