an optimization process for optimizing inputs data relating to a function of a plurality of input - signals for which it is desired to find output values which give an optimum value of the function . such output values are found by performing a plurality of cycles to reach a convergence , each of which cycles includes : providing an old current value of each input signal , selecting a test value of one or more input signals ; generating the function from the selected test values ; and selecting a new current value in dependence upon the relationship between the value of the function for the test value and the value of the function for the old current value . the test values include values close to old current values so as to move the input signal towards a local convergence for the output values . the finding of output values is adapted to perform the cycles such that in some but not all of the cycles , the test value of one or more input signals is selected to lie remotely within the range of the input signal to the old current value , so as to move the input signal towards a global convergence prior to completion of the local convergence .