Memristor

What to observe

1. Start in Manual and push the slider up. Vacancies drift to the right, the doped layer eats into the undoped one, and the resistance falls as it goes. Now let the slider go back to zero. The current stops, the drift stops, and the boundary stays exactly where you left it. That is the whole idea: a resistor whose value is the running total of the charge you have pushed through it.
2. Push the slider down instead and the boundary walks back. The state has no preferred direction and no restoring force, unlike a capacitor, which always wants to discharge. Nothing here is stored as energy, only asposition.
3. Switch to AC and watch the current-voltage panel. It is not a straight line and it is not an ellipse: it is a loop that crosses itself and is pinched shut at the origin. It has to be. The voltage is M·i and M is finite, so when the current is zero the voltage is zero too. No resistor, capacitor or inductor can draw that shape.
4. Now raise the frequency and watch the loop collapse towards a straight line. Faster driving gives the boundary less time to move within a cycle, so the resistance barely changes and the device degenerates into an ordinary resistor. A memristor only looks like a memristor when you drive it slowly enough for its memory to matter.
5. The right-hand panel is the definition rather than a consequence. Charge is the running total of current and flux linkage the running total of voltage, and the traced points sit on one fixed curve in that plane whatever you do to the drive: sine, pulses or by hand. Its slope is M. Resistance, capacitance and inductance are the slopes of the other three such curves.
6. Turn the amplitude up until the boundary slams into either end. The resistance flattens out at R_on or R_off, the loop develops straight segments, and the device stops remembering because there is nowhere left to move. That saturation is what makes it a usable memory cell rather than a curiosity: switch Pulses on and watch it latch between two states.
7. Set the boundary to Sticky. A real dopant boundary slows as it nears an edge, so the drift is throttled there. Drive it hard into a rail and it can no longer come back at all: the state gets stuck against the wall, which is the well-known failure of the simplest window models and the reason the choice of window function is not a cosmetic detail.