1. A method of configuring a configurable memristive device comprising: a memristive matrix, said memristive matrix containing a first dopant species; an emitter electrode, a collector electrode, a programming electrode and a base electrode, said electrodes being in electrical contact with said memristive matrix; and a mobile dopant species different from the first dopant species, said method comprising: applying a programming electrical field between a pair of said electrodes to move said mobile dopant species within said memristive matrix while applying a second electrical field between another pair of said electrodes to control a shape of a distribution of said mobile dopant species within said memristive matrix.