1. After the last generation and before the run() method completes, update the 2 instance attributes: 1) last_generation_parents 2) last_generation_parents_indices. This is to keep the list of parents up-to-date with the latest population fitness last_generation_fitness. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/275
2. 4 methods with names starting with run_. Their purpose is to keep the main loop inside the run() method clean. Check the [Other Methods](https://pygad.readthedocs.io/en/latest/pygad.html#other-methods) section for more information.

Release Date 29 January 2024

1. Solve bugs when multi-objective optimization is used. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/238
2. When the stop_ciiteria parameter is used with the reach keyword, then multiple numeric values can be passed when solving a multi-objective problem. For example, if a problem has 3 objective functions, then stop_criteria="reach_10_20_30" means the GA stops if the fitness of the 3 objectives are at least 10, 20, and 30, respectively. The number values must match the number of objective functions. If a single value found (e.g. stop_criteria=reach_5) when solving a multi-objective problem, then it is used across all the objectives. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/238
3. The delay_after_gen parameter is now deprecated and will be removed in a future release. If it is necessary to have a time delay after each generation, then assign a callback function/method to the on_generation parameter to pause the evolution.
4. Parallel processing now supports calculating the fitness during adaptive mutation. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/201
5. The population size can be changed during runtime by changing all the parameters that would affect the size of any thing used by the GA. For more information, check the [Change Population Size during Runtime](https://pygad.readthedocs.io/en/latest/pygad_more.html#change-population-size-during-runtime) section. https://github.com/ahmedfgad/GeneticAlgorithmPython/discussions/234
6. When a dictionary exists in the gene_space parameter without a step, then mutation occurs by adding a random value to the gene value. The random vaue is generated based on the 2 parameters random_mutation_min_val and random_mutation_max_val. For more information, check the [How Mutation Works with the gene_space Parameter?](https://pygad.readthedocs.io/en/latest/pygad_more.html#how-mutation-works-with-the-gene-space-parameter) section. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/229
7. Add object as a supported data type for int (GA.supported_int_types) and float (GA.supported_float_types). https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/174
8. Use the raise clause instead of the sys.exit(-1) to terminate the execution. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/213
9. Fix a bug when multi-objective optimization is used with batch fitness calculation (e.g. fitness_batch_size set to a non-zero number).
10. Fix a bug in the pygad.py script when finding the index of the best solution. It does not work properly with multi-objective optimization where self.best_solutions_fitness have multiple columns.

         self.best_solution_generation = numpy.where(numpy.array(
             self.best_solutions_fitness) == numpy.max(numpy.array(self.best_solutions_fitness)))[0][0]

1. A new module pygad.utils.nsga2 is created that has the NSGA2 class that includes the functionalities of NSGA-II. The class has these methods: 1) get_non_dominated_set() 2) non_dominated_sorting() 3) crowding_distance() 4) sort_solutions_nsga2(). Check [this section](https://pygad.readthedocs.io/en/latest/pygad_more.html#multi-objective-optimization) for an example.
2. Support of multi-objective optimization using Non-Dominated Sorting Genetic Algorithm II (NSGA-II) using the NSGA2 class in the pygad.utils.nsga2 module. Just return a list, tuple, or numpy.ndarray from the fitness function and the library will consider the problem as multi-objective optimization. All the objectives are expected to be maximization. Check [this section](https://pygad.readthedocs.io/en/latest/pygad_more.html#multi-objective-optimization) for an example.
3. The parent selection methods and adaptive mutation are edited to support multi-objective optimization.
4. Two new NSGA-II parent selection methods are supported in the pygad.utils.parent_selection module: 1) Tournament selection for NSGA-II 2) NSGA-II selection.
5. The plot_fitness() method in the pygad.plot module has a new optional parameter named label to accept the label of the plots. This is only used for multi-objective problems. Otherwise, it is ignored. It defaults to None and accepts a list, tuple, or numpy.ndarray. The labels are used in a legend inside the plot.
6. The default color in the methods of the pygad.plot module is changed to the greenish #64f20c color.
7. A new instance attribute named pareto_fronts added to the pygad.GA instances that holds the pareto fronts when solving a multi-objective problem.
8. The gene_type accepts a list, tuple, or numpy.ndarray for integer data types given that the precision is set to None (e.g. gene_type=[float, [int, None]]).
9. In the cal_pop_fitness() method, the fitness value is re-used if save_best_solutions=True and the solution is found in the best_solutions attribute. These parameters also can help re-using the fitness of a solution instead of calling the fitness function: keep_elitism, keep_parents, and save_solutions.
10. The value 99999999999 is replaced by float('inf') in the 2 methods wheel_cumulative_probs() and stochastic_universal_selection() inside the pygad.utils.parent_selection.ParentSelection class.
11. The plot_result() method in the pygad.visualize.plot.Plot class is removed. Instead, please use the plot_fitness() if you did not upgrade yet.

Release Date 20 June 2023

1. Fix a bug when the initial population has duplciate genes if a nested gene space is used.
2. The gene_space parameter can no longer be assigned a tuple.
3. Fix a bug when the gene_space parameter has a member of type tuple.
4. A new instance attribute called gene_space_unpacked which has the unpacked gene_space. It is used to solve duplicates. For infinite ranges in the gene_space, they are unpacked to a limited number of values (e.g. 100).
5. Bug fixes when creating the initial population using gene_space attribute.
6. When a dict is used with the gene_space attribute, the new gene value was calculated by summing 2 values: 1) the value sampled from the dict 2) a random value returned from the random mutation range defined by the 2 parameters random_mutation_min_val and random_mutation_max_val. This might cause the gene value to exceed the range limit defined in the gene_space. To respect the gene_space range, this release only returns the value from the dict without summing it to a random value.
7. Formatting the strings using f-string instead of the format() method. https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/189
8. In the __init__() of the pygad.GA class, the logged error messages are handled using a try-except block instead of repeating the logger.error() command. https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/189
9. A new class named CustomLogger is created in the pygad.cnn module to create a default logger using the logging module assigned to the logger attribute. This class is extended in all other classes in the module. The constructors of these classes have a new parameter named logger which defaults to None. If no logger is passed, then the default logger in the CustomLogger class is used.
10. Except for the pygad.nn module, the print() function in all other modules are replaced by the logging module to log messages.
11. The callback functions/methods on_fitness(), on_parents(), on_crossover(), and on_mutation() can return values. These returned values override the corresponding properties. The output of on_fitness() overrides the population fitness. The on_parents() function/method must return 2 values representing the parents and their indices. The output of on_crossover() overrides the crossover offspring. The output of on_mutation() overrides the mutation offspring.
12. Fix a bug when adaptive mutation is used while fitness_batch_size>1. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/195
13. When allow_duplicate_genes=False and a user-defined gene_space is used, it sometimes happen that there is no room to solve the duplicates between the 2 genes by simply replacing the value of one gene by another gene. This release tries to solve such duplicates by looking for a third gene that will help in solving the duplicates. These examples explain how it works. Check [this section](https://pygad.readthedocs.io/en/latest/pygad.html#prevent-duplicates-in-gene-values) for more information.
14. Use probabilities to select parents using the rank parent selection method. https://github.com/ahmedfgad/GeneticAlgorithmPython/discussions/205
15. The 2 parameters random_mutation_min_val and random_mutation_max_val can accept iterables (list/tuple/numpy.ndarray) with length equal to the number of genes. This enables customizing the mutation range for each individual gene. https://github.com/ahmedfgad/GeneticAlgorithmPython/discussions/198
16. The 2 parameters init_range_low and init_range_high can accept iterables (list/tuple/numpy.ndarray) with length equal to the number of genes. This enables customizing the initial range for each individual gene when creating the initial population.
17. The data parameter in the predict() function of the pygad.kerasga module can be assigned a data generator. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/115 https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/207
18. The predict() function of the pygad.kerasga module accepts 3 optional parameters: 1) batch_size=None, verbose=0, and steps=None. Check documentation of the [Keras Model.predict()](https://keras.io/api/models/model_training_apis) method for more information. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/207
19. The documentation is updated to explain how mutation works when gene_space is used with int or float data types. Check [this section](https://pygad.readthedocs.io/en/latest/pygad.html#limit-the-gene-value-range-using-the-gene-space-parameter). https://github.com/ahmedfgad/GeneticAlgorithmPython/discussions/198

Fix an issue with passing user-defined function/method for parent selection. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/179

This release has a major change where the fitness function accepts a mandatory parameter referring to the instance of the pygad.GA class.

This is the release notes:

1. The structure of the library is changed and some methods defined in the pygad.py module are moved to the pygad.utils, pygad.helper, and pygad.visualize submodules.
2. The pygad.utils.parent_selection module has a class named ParentSelection where all the parent selection operators exist. The pygad.GA class extends this class.
3. The pygad.utils.crossover module has a class named Crossover where all the crossover operators exist. The pygad.GA class extends this class.
4. The pygad.utils.mutation module has a class named Mutation where all the mutation operators exist. The pygad.GA class extends this class.
5. The pygad.helper.unique module has a class named Unique some helper methods exist to solve duplicate genes and make sure every gene is unique. The pygad.GA class extends this class.
6. The pygad.visualize.plot module has a class named Plot where all the methods that create plots exist. The pygad.GA class extends this class.

...
class GA(utils.parent_selection.ParentSelection, 
         utils.crossover.Crossover, 
         utils.mutation.Mutation, 
         helper.unique.Unique,
         visualize.plot.Plot):
...

2. Support of using the logging module to log the outputs to both the console and text file instead of using the print() function. This is by assigning the logging.Logger to the new logger parameter. Check the [Logging Outputs](https://pygad.readthedocs.io/en/latest/README_pygad_ReadTheDocs.html#logging-outputs) for more information.
3. A new instance attribute called logger to save the logger.
4. The function/method passed to the fitness_func parameter accepts a new parameter that refers to the instance of the pygad.GA class. Check this for an example: [Use Functions and Methods to Build Fitness Function and Callbacks](https://pygad.readthedocs.io/en/latest/README_pygad_ReadTheDocs.html#use-functions-and-methods-to-build-fitness-and-callbacks). https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/163
5. Update the documentation to include an example of using functions and methods to calculate the fitness and build callbacks. Check this for more details: [Use Functions and Methods to Build Fitness Function and Callbacks](https://pygad.readthedocs.io/en/latest/README_pygad_ReadTheDocs.html#use-functions-and-methods-to-build-fitness-and-callbacks). https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/92#issuecomment-1443635003
6. Validate the value passed to the initial_population parameter.
7. Validate the type and length of the pop_fitness parameter of the best_solution() method.
8. Some edits in the documentation. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/106
9. Fix an issue when building the initial population as (some) genes have their value taken from the mutation range (defined by the parameters random_mutation_min_val and random_mutation_max_val) instead of using the parameters init_range_low and init_range_high.
10. The summary() method returns the summary as a single-line string. Just log/print the returned string it to see it properly.
11. The callback_generation parameter is removed. Use the on_generation parameter instead.
12. There was an issue when using the parallel_processing parameter with Keras and PyTorch. As Keras/PyTorch are not thread-safe, the predict() method gives incorrect and weird results when more than 1 thread is used. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/145 https://github.com/ahmedfgad/TorchGA/issues/5 https://github.com/ahmedfgad/KerasGA/issues/6. Thanks to this [StackOverflow answer](https://stackoverflow.com/a/75606666/5426539).
13. Replace numpy.float by float in the 2 parent selection operators roulette wheel and stochastic universal. https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/168

1. Fix an issue when paralell processing was used where the elitism solutions' fitness values are not re-used. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/160#issuecomment-1441718184

1. A new summary() method is supported to return a Keras-like summary of the PyGAD lifecycle.
2. A new optional parameter called fitness_batch_size is supported to calculate the fitness function in batches. If it is assigned the value 1 or None (default), then the normal flow is used where the fitness function is called for each individual solution. If the fitness_batch_size parameter is assigned a value satisfying this condition 1 < fitness_batch_size <= sol_per_pop, then the solutions are grouped into batches of size fitness_batch_size and the fitness function is called once for each batch. In this case, the fitness function must return a list/tuple/numpy.ndarray with a length equal to the number of solutions passed. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/136.
3. The cloudpickle library (https://github.com/cloudpipe/cloudpickle) is used instead of the pickle library to pickle the pygad.GA objects. This solves the issue of having to redefine the functions (e.g. fitness function). The cloudpickle library is added as a dependancy in the requirements.txt file. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/159
4. Support of assigning methods to these parameters: fitness_func, crossover_type, mutation_type, parent_selection_type, on_start, on_fitness, on_parents, on_crossover, on_mutation, on_generation, and on_stop. https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/92 https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/138
5. Validating the output of the parent selection, crossover, and mutation functions.
6. The built-in parent selection operators return the parent's indices as a NumPy array.
7. The outputs of the parent selection, crossover, and mutation operators must be NumPy arrays.
8. Fix an issue when allow_duplicate_genes=True. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/39
9. Fix an issue creating scatter plots of the solutions' fitness.
10. Sampling from a set() is no longer supported in Python 3.11. Instead, sampling happens from a list(). Thanks Marco Brenna for pointing to this issue.
11. The lifecycle is updated to reflect that the new population's fitness is calculated at the end of the lifecycle not at the beginning. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/154#issuecomment-1438739483
12. There was an issue when save_solutions=True that causes the fitness function to be called for solutions already explored and have their fitness pre-calculated. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/160
13. A new instance attribute named last_generation_elitism_indices added to hold the indices of the selected elitism. This attribute helps to re-use the fitness of the elitism instead of calling the fitness function.
14. Fewer calls to the best_solution() method which in turns saves some calls to the fitness function.
15. Some updates in the documentation to give more details about the cal_pop_fitness() method. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/79#issuecomment-1439605442

PyGAD 2.18.2 release notes

1. Remove numpy.int and numpy.float from the list of supported data types. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/151 https://github.com/ahmedfgad/GeneticAlgorithmPython/pull/152
2. Call the on_crossover() callback function even if crossover_type is None. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/138
3. Call the on_mutation() callback function even if mutation_type is None. https://github.com/ahmedfgad/GeneticAlgorithmPython/issues/138