1. A memristive cross-bar array for determining a dot product, comprising: a plurality of row lines; a plurality of column lines intersecting the row lines to form respective junctions; a plurality of resistive memory elements coupled between the row lines and the column lines at the junctions, the row lines to provide programming signals to the resistive memory elements, the programming signals defining matrix values within a matrix of the resistive memory elements; and the row lines to provide vector signals at the resistive memory elements, the vector signals defining vector values to be applied to the resistive memory elements; a current collection line to collect all currents output from the resistive memory elements through the respective column lines, the collected currents equaling a dot product of the matrix values and the vector values; and circuits connected to the row lines to apply a reference voltage to shift an operation region of the memristive cross-bar array based on the reference voltage.