The Scheduler

The Patchworks includes a solver algorithm that develops harvest schedules that best meet the set of active targets. The problem that the solver algorithm is tackling is very challenging, because it is dealing with a spatially-explicit combinatorial problem. In operations research terms the problem is 'non-polynomial complete', and the characteristic of this type of problem is that for reasonably-sized problems the solution cannot be found in a reasonable amount of time. In many cases the best solution can only be found be exhaustively examining all possible solutions, anc keeping track of the best case. In practical terms, this may require centuries of computer time.

Rather than taking a very long time to find the best solution, the solver in Patchworks finds quite good solutions in a reasonably short period of time. The solver algorithm is based on a 'stochastic meta-heuristic' that employs random draws, a variety of perturbation schemes, and a controlled acceptance of new states in order to incrementally build a good harvest schedule. Since the prime activity of the solver is to schedule the order of forest management treatments, the name given to this process is the 'scheduler'.

When the scheduler is activated the Patchworks will begin altering the harvest schedule by adding, adjusting, and removing harvest treatments. This process continues indefinitely as long as the algorithm is able to find changes to the harvest schedule that improve the quality of the solution with respect to the section called “The Goal Programming Formulation”.