genetics.lua

require "node"

function adjusted_fitness(standard_fitness)
   local denominator = 1 + standard_fitness
   return 1 / denominator
end

function generate_full(functions, terminals, max_depth)
   local root = nil
   if max_depth > 1 then
	  -- Keep going! 
	  local node = functions[math.random(table.getn(functions))]
	  root = new_node(node.arity, node.value)
   else
	  -- Time for a terminal
	  local node = terminals[math.random(table.getn(terminals))]
	  root = new_node(node.arity, node.value)
   end
   
   -- Assign child nodes recursively
   if root.arity > 0 then
	  for i = 1,root.arity do
		 add_child(root, generate_full(functions, terminals, max_depth - 1))
	  end
   end
   return root
end

function generate_grow(functions, terminals, max_depth)
   local root = nil
   if max_depth > 1 then
	  -- Function or terminal?
	  choose_func = math.random(2) == 1
	  if choose_func then
		 node = functions[math.random(table.getn(functions))]
		 root = new_node(node.arity, node.value)
	  else
		 node = terminals[math.random(table.getn(terminals))]
		 root = new_node(node.arity, node.value)
	  end
   else
	  -- Choose a terminal
	  node = terminals[math.random(table.getn(terminals))]
	  root = new_node(node.arity, node.value)
   end

   if root.arity > 0 then
	  for i = 1,root.arity do
		 add_child(root, generate_grow(functions, terminals, max_depth - 1))
	  end
   end

   return root
end

function random_select_subtree(root)
   local keep_going = math.random(2) == 1
   if keep_going then
	  if root.child_count > 0 then
		 local next_node = root.children[math.random(root.child_count)-1]
		 return random_select_subtree(next_node)
	  else
		 return root
	  end
   else
	  return root
   end
end

function subtree_crossover(father, mother)
   local offspring = clone_node(mother)
   replace_child(offspring, math.random(offspring.child_count)-1, random_select_subtree(father))
   return offspring
end