1. A data processing apparatus comprising: data processing logic operable to perform data processing operations specified by program instructions, said data processing logic comprising a plurality of functional units configured to execute in parallel, said data processing operations being performed on data received from a data source; a decoder responsive to a single program instruction to control said data processing logic to concurrently execute said single program instruction on each of a plurality of vector elements of each of a respective plurality of vector input operands received from said data source using said plurality of functional units; wherein during execution of said single program instruction, said plurality of functional units operate as a predetermined group on said plurality of vector elements to perform at least a matrix-vector calculation in which said matrix is a non-identity matrix and entries of said matrix are one of: (i) populated in dependence upon at least one of said vector elements of at least one of said plurality of vector input operands; and (ii) generated within said data processing logic as an explicit function of said single program instruction.