Tasks are executed in a multiprocessing system with a master processor core (10) and a plurality of slave processor cores (12). The master processor core (10), executes a program that defines a matrix of tasks at respective positions in the matrix and a task dependency pattern applicable to a plurality of the tasks and defined relative to the positions. Each dependency pattern defines relative dependencies for a plurality of positions in the matrix, rather than using individual dependencies for individual positions. In response to the program the master processor core (10) dynamically stores definitions of current task dependency patterns in a dependency pattern memory. A hardware task scheduler computes the positions of the tasks that are ready for execution at run time from information from information about positions for which tasks have been completed and the task dependency pattern applied relative to those tasks. The tasks that have been computed to be ready for execution are assigned to the slave processor cores (12).