# Genetic Network Programming #

## Name #

Genetic Network Programming (GNP)

## Taxonomy #

Genetic Network Programming is a technique that combines genetic algorithms and graph-based program representation for evolutionary optimization and learning. It is closely related to genetic programming and evolutionary algorithms.

- Computational Intelligence
- Biologically Inspired Computation
- Evolutionary Computation
- Evolutionary Algorithms
- Genetic Algorithms
- Genetic Programming
- Genetic Network Programming

- Evolutionary Algorithms

- Evolutionary Computation

- Biologically Inspired Computation

## Strategy #

Genetic Network Programming represents solutions as directed graph structures called GNP individuals. Each node in the graph contains processing functions and connections to other nodes, enabling the execution of complex behaviors. The graph structure allows for conditional branching and iterative processing, providing a flexible and expressive representation for evolving programs.

The GNP algorithm follows an evolutionary process to optimize the graph-based programs. It starts with an initial population of randomly generated GNP individuals. Each individual is evaluated based on a fitness function that measures its performance on a given task. The fittest individuals are selected for reproduction, where genetic operators like crossover and mutation are applied to create a new generation of offspring. This process is repeated iteratively, with each generation improving upon the previous one, until a satisfactory solution is found or a termination criterion is met.

The graph structure of GNP allows for the evolution of modular and hierarchical programs. Nodes can represent high-level functions or subtasks, and the connections between nodes determine the flow of execution. This modular representation enables the reuse of subprograms and the evolution of complex behaviors through the combination of simpler components.

## Procedure #

- Initialization:
- Define the problem and specify the fitness function.
- Set the population size, crossover rate, mutation rate, and other parameters.
- Create an initial population of random GNP individuals.

- Evaluation:
- Execute each GNP individual on the given task.
- Calculate the fitness score for each individual based on its performance.

- Selection:
- Select a subset of individuals from the population based on their fitness scores.
- Common selection methods include tournament selection, roulette wheel selection, or rank-based selection.

- Reproduction:
- Crossover:
- Randomly select pairs of parent individuals from the selected subset.
- Apply the crossover operator to exchange genetic material between the parent individuals.
- Create new offspring individuals by combining the genetic material of the parents.

- Mutation:
- Apply the mutation operator to introduce random changes in the offspring individuals.
- Mutation can modify node functions, connection weights, or graph structure.

- Crossover:
- Replacement:
- Replace a portion of the population with the newly created offspring individuals.
- Common replacement strategies include generational replacement or steady-state replacement.

- Termination:
- Check if the termination criteria are met, such as reaching a maximum number of generations or finding a satisfactory solution.
- If the criteria are not met, go back to step 2 and continue the evolutionary process.
- If the criteria are met, return the best GNP individual found as the solution.

### Data Structures #

- GNP Individual: Represents a candidate solution as a directed graph.
- Nodes: Contain processing functions and connections to other nodes.
- Connections: Represent the flow of execution between nodes.

- Population: Stores a collection of GNP individuals.
- Fitness Function: Evaluates the performance of a GNP individual on the given task.

### Parameters #

- Population Size: The number of GNP individuals in each generation.
- Crossover Rate: The probability of applying the crossover operator to a pair of parent individuals.
- Mutation Rate: The probability of applying the mutation operator to an offspring individual.
- Maximum Generations: The maximum number of iterations before terminating the algorithm.

## Considerations #

### Advantages #

- Flexibility: GNP can represent complex programs and behaviors through its graph-based structure.
- Modularity: The graph representation allows for the evolution of modular and hierarchical programs.
- Expressiveness: GNP can evolve programs with conditional branching and iterative processing.

### Disadvantages #

- Computational Complexity: Evaluating and evolving graph-based programs can be computationally expensive.
- Parameter Tuning: The performance of GNP depends on the proper selection of parameters, which may require experimentation.
- Interpretability: The evolved graph structures can be complex and difficult to interpret.

## Heuristics #

### Population Size #

- Start with a population size that provides sufficient diversity for exploration.
- Increase the population size for more complex problems or larger search spaces.
- Consider the trade-off between computational resources and population diversity.

### Crossover and Mutation Rates #

- Set the crossover rate high enough to promote the exchange of genetic material between individuals.
- Keep the mutation rate relatively low to avoid disrupting good solutions.
- Adjust the rates based on the problem complexity and desired exploration-exploitation balance.

### Graph Structure #

- Design the initial graph structure to capture the essential components and relationships of the problem.
- Allow for the evolution of graph structures to enable the discovery of novel solutions.
- Consider incorporating domain-specific knowledge or constraints into the graph representation.

### Fitness Function #

- Define a fitness function that accurately measures the performance of GNP individuals on the given task.
- Ensure that the fitness function is efficient to compute and provides a meaningful gradient for selection.
- Consider incorporating multiple objectives or constraints into the fitness evaluation if required by the problem.

### Termination Criteria #

- Set a maximum number of generations to prevent excessive computation.
- Define a convergence criterion based on the fitness improvement or diversity of the population.
- Allow for early termination if a satisfactory solution is found.