Vector-matrix multiplication is the basic operation of neural calculations. Generation of the conductivity matrix of a variable-resistor array, which is used to do this sort of multiplication, requires the arbitrary change of resistor conductances using a limited number of control signals, which are voltages on conductors of a crossbar type structure. Since the number of conductors is much less than the number of resistors, this procedure includes multiple steps. At each step the conductances of target resistors change. The number of such resistors is not greater than the number of control signals. At the same time, the conductances of some non-target resistors undergo inevitable changes. These changes must be compensated. The paper considers high-frequency harmonic signals of the same amplitude and frequency, but with different phases as control signals for generating conductivity matrices. The analysis of a simple resistor model proves the possibility to produce any conductivity matrix in a certain range. At each step a row or column of the matrix is generated (changed). The conditions securing realizability and convenience of the process are discussed.