@@ -4237,6 +4237,48 @@ It accepts an integer and defaults to -1. It set to ``-1`` or a positive
42374237integer, then it keeps the parents of one generation available in the
42384238next generation.
42394239
4240+ Why the Fitness Function is not Called for Solution at Index 0?
4241+ ===============================================================
4242+ 4243+ PyGAD has a parameter called ``keep_elitism `` which defaults to 1. This
4244+ parameter defines the number of best solutions in generation **X ** to
4245+ keep in the next generation **X+1 **. The best solutions are just copied
4246+ from generation **X ** to generation **X+1 ** without making any change.
4247+ 4248+ .. code :: python
4249+
4250+ ga_instance = pygad.GA(... ,
4251+ keep_elitism = 1 ,
4252+ ... )
4253+
4254+ The best solutions are copied at the beginning of the population. If
4255+ ``keep_elitism=1 ``, this means the best solution in generation X is kept
4256+ in the next generation X+1 at index 0 of the population. If
4257+ ``keep_elitism=2 ``, this means the 2 best solutions in generation X are
4258+ kept in the next generation X+1 at indices 0 and 1 of the population of
4259+ generation 1.
4260+ 4261+ Because the fitness of these best solutions are already calculated in
4262+ generation X, then their fitness values will not be recalculated at
4263+ generation X+1 (i.e. the fitness function will not be called for these
4264+ solutions again). Instead, their fitness values are just reused. This is
4265+ why you see that no solution with index 0 is passed to the fitness
4266+ function.
4267+ 4268+ To force calling the fitness function for each solution in every
4269+ generation, consider setting ``keep_elitism `` and ``keep_parents `` to 0.
4270+ Moreover, keep the 2 parameters ``save_solutions `` and
4271+ ``save_best_solutions `` to their default value ``False ``.
4272+ 4273+ .. code :: python
4274+
4275+ ga_instance = pygad.GA(... ,
4276+ keep_elitism = 0 ,
4277+ keep_parents = 0 ,
4278+ save_solutions = False ,
4279+ save_best_solutions = False ,
4280+ ... )
4281+
42404282Batch Fitness Calculation
42414283=========================
42424284
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