NeatChromosomeSpec.java

package net.bmahe.genetics4j.neat.spec;

import org.apache.commons.lang3.Validate;

import org.immutables.value.Value;

import net.bmahe.genetics4j.core.spec.chromosome.ChromosomeSpec;

/**

 * Specification for NEAT (NeuroEvolution of Augmenting Topologies) neural network chromosomes.

 * 

 * <p>NeatChromosomeSpec defines the structural parameters and constraints for creating NEAT neural network chromosomes.

 * This specification is used by chromosome factories to generate initial network topologies and by genetic operators to

 * understand network boundaries and weight constraints.

 * 

 * <p>Key parameters:

 * <ul>

 * <li><strong>Network topology</strong>: Defines the number of input and output nodes</li>

 * <li><strong>Weight constraints</strong>: Specifies minimum and maximum connection weight values</li>

 * <li><strong>Network structure</strong>: Establishes the foundation for topology evolution</li>

 * <li><strong>Genetic boundaries</strong>: Provides constraints for mutation and crossover operations</li>

 * </ul>

 * 

 * <p>NEAT network architecture:

 * <ul>

 * <li><strong>Input layer</strong>: Fixed number of input nodes (indices 0 to numInputs-1)</li>

 * <li><strong>Output layer</strong>: Fixed number of output nodes (indices numInputs to numInputs+numOutputs-1)</li>

 * <li><strong>Hidden layers</strong>: Variable number of hidden nodes added through evolution</li>

 * <li><strong>Connections</strong>: Weighted links between nodes with enable/disable states</li>

 * </ul>

 * 

 * <p>Common usage patterns:

 * 

 * <pre>{@code

 * // Simple XOR problem specification

 * NeatChromosomeSpec xorSpec = NeatChromosomeSpec.of(

 * 		2, // 2 inputs (A, B)

 * 			1, // 1 output (A XOR B)

 * 			-1.0f, // minimum weight

 * 			1.0f // maximum weight

 * );

 * 

 * // Complex classification problem

 * NeatChromosomeSpec classificationSpec = NeatChromosomeSpec.of(

 * 		784, // 28x28 pixel inputs

 * 			10, // 10 class outputs

 * 			-2.0f, // wider weight range

 * 			2.0f);

 * 

 * // Builder pattern for complex construction

 * NeatChromosomeSpec spec = new NeatChromosomeSpec.Builder().numInputs(5)

 * 		.numOutputs(3)

 * 		.minWeightValue(-1.5f)

 * 		.maxWeightValue(1.5f)

 * 		.build();

 * }</pre>

 * 

 * <p>Integration with NEAT ecosystem:

 * <ul>

 * <li><strong>Chromosome factories</strong>: Used by NeatConnectedChromosomeFactory for initial network generation</li>

 * <li><strong>Genetic operators</strong>: Provides constraints for weight mutations and structural changes</li>

 * <li><strong>Network evaluation</strong>: Defines input/output interfaces for fitness computation</li>

 * <li><strong>Evolution configuration</strong>: Establishes network parameters for entire evolutionary run</li>

 * </ul>

 * 

 * <p>Weight constraint management:

 * <ul>

 * <li><strong>Mutation boundaries</strong>: Weight mutations respect min/max bounds</li>

 * <li><strong>Initial generation</strong>: New connections use weights within specified range</li>

 * <li><strong>Crossover inheritance</strong>: Parent weights may be clipped to child bounds</li>

 * <li><strong>Network stability</strong>: Bounded weights help prevent gradient explosion/vanishing</li>

 * </ul>

 * 

 * <p>Validation and constraints:

 * <ul>

 * <li><strong>Positive node counts</strong>: Both input and output counts must be greater than zero</li>

 * <li><strong>Weight ordering</strong>: Minimum weight value should be less than maximum (not enforced)</li>

 * <li><strong>Reasonable bounds</strong>: Weight ranges should be appropriate for the problem domain</li>

 * <li><strong>Network capacity</strong>: Input/output counts should match problem requirements</li>

 * </ul>

 * 

 * <p>Problem domain considerations:

 * <ul>

 * <li><strong>Classification</strong>: Output count should match number of classes</li>

 * <li><strong>Regression</strong>: Single or multiple outputs for continuous value prediction</li>

 * <li><strong>Control problems</strong>: Outputs correspond to control signals or actions</li>

 * <li><strong>Feature extraction</strong>: Input count should match feature dimensionality</li>

 * </ul>

 * 

 * @see net.bmahe.genetics4j.neat.chromosomes.NeatChromosome

 * @see net.bmahe.genetics4j.neat.chromosomes.factory.NeatConnectedChromosomeFactory

 * @see net.bmahe.genetics4j.core.spec.EAConfiguration

 * @see ChromosomeSpec

 */

@Value.Immutable

	/**

	 * Returns the number of input nodes for the neural network.

	 * 

	 * <p>Input nodes receive external data and form the first layer of the network. They are assigned indices 0 through

	 * numInputs-1 and do not apply activation functions to their values.

	 * 

	 * @return the number of input nodes (must be positive)

	 */

	@Value.Parameter

	public abstract int numInputs();

	/**

	 * Returns the number of output nodes for the neural network.

	 * 

	 * <p>Output nodes produce the final results of network computation and form the last layer of the network. They are

	 * assigned indices numInputs through numInputs+numOutputs-1 and apply activation functions to their weighted sums.

	 * 

	 * @return the number of output nodes (must be positive)

	 */

	@Value.Parameter

	public abstract int numOutputs();

	/**

	 * Returns the minimum allowed connection weight value.

	 * 

	 * <p>This constraint is used by genetic operators to bound weight mutations and ensure network stability. New

	 * connections and weight perturbations should respect this lower bound.

	 * 

	 * @return the minimum connection weight value

	 */

	@Value.Parameter

	public abstract float minWeightValue();

	/**

	 * Returns the maximum allowed connection weight value.

	 * 

	 * <p>This constraint is used by genetic operators to bound weight mutations and ensure network stability. New

	 * connections and weight perturbations should respect this upper bound.

	 * 

	 * @return the maximum connection weight value

	 */

	@Value.Parameter

	public abstract float maxWeightValue();

	@Value.Check

	protected void check() {

	}

	/**

	 * Creates a new NEAT chromosome specification with the given parameters.

	 * 

	 * <p>This is a convenience factory method for creating chromosome specifications with all required parameters. The

	 * specification will be validated to ensure positive input and output counts.

	 * 

	 * @param numInputs      number of input nodes (must be positive)

	 * @param numOutputs     number of output nodes (must be positive)

	 * @param minWeightValue minimum allowed connection weight

	 * @param maxWeightValue maximum allowed connection weight

	 * @return a new chromosome specification with the specified parameters

	 * @throws IllegalArgumentException if numInputs <= 0 or numOutputs <= 0

	 */

	public static NeatChromosomeSpec of(final int numInputs, final int numOutputs, final float minWeightValue,

			final float maxWeightValue) {

	}

}

Mutations