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 transistor comprising a gate connected to a line to instruct setting of the bi-polar memristor; a second conductive path connecting the bi-polar memristor to the voltage input and the circuit ground, the second conductive path including a second transistor comprising a gate connected to a line to instruct re-setting of a bi-polar memristor; in a first configuration of the circuit, the first transistor is closed and the second transistor 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 transistor is open and the second transistor is closed, such that when the 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.