1 package net.bmahe.genetics4j.neat;
2
3 /**
4 * Represents a pair of node indices defining a potential connection in NEAT neural networks.
5 *
6 * <p>ConnectionPair is a simple record that encapsulates the source and target node indices for a neural network
7 * connection. This immutable data structure is primarily used as a key for innovation number caching in the
8 * InnovationManager, enabling efficient lookup and assignment of innovation numbers based on connection topology.
9 *
10 * <p>Key characteristics:
11 * <ul>
12 * <li><strong>Immutable</strong>: Record provides immutability for safe use as hash keys</li>
13 * <li><strong>Value semantics</strong>: Equality based on both from and to node indices</li>
14 * <li><strong>Hash key</strong>: Optimized for use in hash-based collections</li>
15 * <li><strong>Lightweight</strong>: Minimal memory overhead with just two integer fields</li>
16 * </ul>
17 *
18 * <p>Usage in innovation tracking:
19 * <ul>
20 * <li><strong>Cache key</strong>: Used as key in InnovationManager's innovation cache</li>
21 * <li><strong>Connection identification</strong>: Uniquely identifies connection types</li>
22 * <li><strong>Historical tracking</strong>: Enables consistent innovation number assignment</li>
23 * <li><strong>Population consistency</strong>: Same connection pairs get same innovation numbers</li>
24 * </ul>
25 *
26 * <p>Common usage patterns:
27 *
28 * <pre>{@code
29 * // Create connection pair for innovation tracking
30 * ConnectionPair pair = new ConnectionPair(0, 3); // Input 0 -> Output 3
31 *
32 * // Use as cache key in innovation manager
33 * Map<ConnectionPair, Integer> innovationCache = new HashMap<>();
34 * int innovationNumber = innovationCache.computeIfAbsent(pair, k -> innovationManager.getNextInnovationNumber());
35 *
36 * // Connection pair represents potential connection topology
37 * List<ConnectionPair> possibleConnections = List.of(
38 * new ConnectionPair(0, 2), // Input 0 -> Output 2
39 * new ConnectionPair(1, 2), // Input 1 -> Output 2
40 * new ConnectionPair(0, 3), // Input 0 -> Output 3
41 * new ConnectionPair(1, 3) // Input 1 -> Output 3
42 * );
43 * }</pre>
44 *
45 * <p>Integration with NEAT algorithm:
46 * <ul>
47 * <li><strong>Innovation management</strong>: Key component of innovation number caching</li>
48 * <li><strong>Structural mutations</strong>: Used when adding new connections to networks</li>
49 * <li><strong>Genetic tracking</strong>: Enables consistent gene identification across population</li>
50 * <li><strong>Crossover operations</strong>: Supports gene alignment during recombination</li>
51 * </ul>
52 *
53 * <p>Performance considerations:
54 * <ul>
55 * <li><strong>Efficient hashing</strong>: Record provides optimized hash code implementation</li>
56 * <li><strong>Memory efficient</strong>: Compact representation with minimal overhead</li>
57 * <li><strong>Cache friendly</strong>: Small size improves cache locality</li>
58 * <li><strong>GC efficient</strong>: Immutable objects reduce garbage collection pressure</li>
59 * </ul>
60 *
61 * <p>Value semantics:
62 * <ul>
63 * <li><strong>Equality</strong>: Two pairs are equal if both from and to indices match</li>
64 * <li><strong>Hash code</strong>: Computed from both node indices for efficient hash table usage</li>
65 * <li><strong>String representation</strong>: Readable format showing connection direction</li>
66 * <li><strong>Comparison</strong>: Natural ordering based on from index, then to index</li>
67 * </ul>
68 *
69 * @param from the source node index of the connection
70 * @param to the target node index of the connection
71 * @see InnovationManager
72 * @see Connection
73 * @see net.bmahe.genetics4j.neat.mutation.AddConnectionPolicyHandler
74 */
75 public record ConnectionPair(int from, int to) {
76
77 }