Specify a weighting for the combination of multiple goals.
This weighting is used to modify the contribution of the combination goals error to the
global error during the fitness evaluation. The global error in each level of the tree
is computed by taking the evaluated error of each goal, multiplying it by the indicated
weighting factor, and then summing all of the resultant weighted errors in each
branch-level of the tree.
Note: The weighting of each goal is shown in brackets next to
the tree representation of the goal.