1. A method for programmed-state detection of memristor stacks comprising: applying a first secondary switching voltage across a memristor stack to produce a first programmed-state-dependent secondary switching response in a memristor in the memristor stack, the programmed-state-dependent secondary switching response producing a change in the electrical resistance of the memristor stack; measuring a first electrical resistance of the memristor stack; and inferring the programmed state of the memristor stack from the measured electrical resistance.