An alternative strategy suggested by Parks [49] is to generate solutions according to the formula:

where is now a vector of random numbers in the range and is a diagonal matrix which defines the maximum change allowed in each variable. After a successful trial, i.e. after an accepted change in the solution, is updated:

where and perform similar roles and is a diagonal matrix the elements of which consist of the magnitudes of the successful changes made to each control variable. This tunes the maximum step size associated with each control variable towards a value giving acceptable changes.