1. A circuit comprising: a voltage input; a bi-polar memristor; a first conductive path connecting the bi-polar memristor to the voltage input and a circuit ground; the first conductive path including a first switch; a second conductive path connecting the bi-polar memristor to the voltage input and the circuit ground; the second conductive path including a second switch; in a first configuration of the circuit, the first switch is closed and the second switch is open, such that when a first polarity of voltage is supplied to the voltage input, current can flow along the first conductive path and through the bi-polar memristor in a first direction; and in a second configuration of the circuit, the first switch is open and the second switch is closed, such that when a first polarity of voltage is supplied to the voltage input, current can flow along the second conductive path and through the bi-polar memristor in a second direction that is opposite to the first direction.