# Changes between Version 7 and Version 8 of Documentation/Reference/Genetic Programming Crossovers

Ignore:
Timestamp:
07/23/14 17:38:21 (8 years ago)
Comment:

 v7 - The behavioral distances between node ''i'' and every node ''j'' from parent1 are computed using a formula that takes into account the minimum and maximum values computed by the two nodes during evaluation: [[Image(http://dev.heuristiclab.com/trac/hl/core/raw-attachment/wiki/Crossovers/01-PFX-behavioral-distance.png)]] [[Image(01-PFX-behavioral-distance.png)]] - Once all the behavioral distances between node ''i'' and every node ''j'' have been calculated, they are normalized: [[Image(http://dev.heuristiclab.com/trac/hl/core/raw-attachment/wiki/Crossovers/02-PFX-normalized-behavioral-distance.png)]] [[Image(02-PFX-normalized-behavioral-distance.png)]] and turned into selection probabilities (weights): [[Image(http://dev.heuristiclab.com/trac/hl/core/raw-attachment/wiki/Crossovers/03-PFX-selection-probabilities.png)]] [[Image(03-PFX-selection-probabilities.png)]] - A node   from the second parent is probabilistically chosen and swapped with node ''i'' from the first parent - The sampling semantic distance (SSD) between two nodes (subtrees) is defined as the absolute mean between their corresponding sampling semantics: [[Image(http://dev.heuristiclab.com/trac/hl/core/raw-attachment/wiki/Crossovers/04-SSX-sampling-semantic-distance.png)]] [[Image(04-SSX-sampling-semantic-distance.png)]] where S1 and S2 are the two subtrees, and ''U'', ''V'' are their respective sampling semantics. - Two nodes are deemed similar if their SSD falls within a predefined interval [alfa,beta]: [[Image(http://dev.heuristiclab.com/trac/hl/core/raw-attachment/wiki/Crossovers/05-SSX-similarity-condition.png)]] [[Image(05-SSX-similarity-condition.png)]] The crossover procedure chooses a crossover point from parent0, then picks the first node in parent1 that satisfies the similarity condition (5).