In this block diagram e is the vector of error signals, which the controller attempts to minimise, d is the vector of disturbance signals, u is the vector of control signals, x is the reference signal, R is the matrix of filtered reference signals, G represents the physical responses between the control sources and the error sensors, bG is a model of this plant response used in the control update algorithm, W represents the control filters and a is the convergence gain which determines the speed of adaptation for the controller.