  We describe the implementation of output code optimization in the open source
computer algebra system FORM. This implementation is based on recently
discovered techniques of Monte Carlo tree search to find efficient multivariate
Horner schemes, in combination with other optimization algorithms, such as
common subexpression elimination. For systems for which no specific knowledge
is provided it performs significantly better than other methods we could
compare with. Because the method has a number of free parameters, we also show
some methods by which to tune them to different types of problems.
