You might have heard about the theory of evolution by natural selection. If not then read this quote by Charles Darwin ” It is not the strongest of the species that survives, nor the most intelligent; it is the one most adaptable to change. ” Genetic Algorithm is also based on this theory.
In the 1970’s, Jon Holland tries to mimic some processes observed in natural evolution by introducing genetic algorithm. This algorithm can be used in optimization and search problems both.
A typical genetic algorithm requires some population in the solution domain and a fitness function to find the fittest individual. To evolve individuals in the population genetic algorithm uses some operations like crossover, mutation, and selection.
Genetic algorithm starts with some random initial population. Then tries to produce offspring from the best individuals in the population. The concept is that, if the fittest individuals are selected then chances of producing a better offspring is more. This process keeps on iteration until your target is not achieved. Each iteration is known as the generation.
Initial Population
Initial Population refers to a set of possible solutions. Each member (individual) of the population is usually known as the chromosome (phenotypes) and represents a solution for the problem to be investigated. The chromosome is represented as a set of parameters (features or genes or weights) that defines the individual. Size of the population depends totally on your problem. Random selection of initial population makes sure that it covers a wide range of possible solution.
Evaluation and Fitness Function
Now, we have a random initial population, next thing is to evaluate the fitness of these individuals. To evaluate the fitness of these individuals, you need to define some fitness function. You need to choose the fitness function according to your problem. Fitness function measures the quality of each individual.
Selection
Some best individuals are selected from the evaluated population. These selected individuals are mated to produce some new offspring.
Crossover
Each individual selected in the previous step has some quality. Our objective is to produce better offspring so that our algorithm can evolve and find a better solution to the problem. To do that two individuals from the best population are selected and a new child (offspring) is produced with features of both as shown above. This is known as Crossover.
Mutation
Mutation is applied to maintain the diversity within the population and inhibit premature convergence. With some low probability, a portion of the new individual is subjected to mutation as shown in the figure above.
Replacement
New population replaces a previous one for the next generation. This process keeps on iterating until a certain target is not achieved.
Application of genetic algorithm in neural networks:
- Training of a neural network ( instead of using gradient descent, Adam etc.)
- Selection of neural network architecture ( Hyperparameters selection)
Now, you might have got some feeling about the genetic algorithm. In the next blog, we will see how this concept can be applied to train the neural network to play a snake game. Hope you enjoy reading.
If you have any doubt/suggestion please feel free to ask and I will do my best to help or improve myself. Good-bye until next time.