Documentation of 'ec.gp.koza.CrossoverPipeline' Java class
CrossoverPipeline
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ec.gp.koza

Class CrossoverPipeline

  • All Implemented Interfaces:
    Prototype, Setup, SteadyStateBSourceForm, RandomChoiceChooserD, java.io.Serializable, java.lang.Cloneable

    public class CrossoverPipeline
extends GPBreedingPipeline
    CrossoverPipeline is a GPBreedingPipeline which performs a strongly-typed version of Koza-style "Subtree Crossover". Two individuals are selected, then a single tree is chosen in each such that the two trees have the same GPTreeConstraints. Then a random node is chosen in each tree such that each node's return type is type-compatible with the argument type of the slot in the parent which contains the other node. If by swapping subtrees at these nodes the two trees will not violate maximum depth constraints, then the trees perform the swap, otherwise, they repeat the hunt for random nodes.

    The pipeline tries at most tries times to a pair of random nodes BOTH with valid swap constraints. If it cannot find any such pairs after tries times, it uses the pair of its last attempt. If either of the nodes in the pair is valid, that node gets substituted with the other node. Otherwise an individual invalid node isn't changed at all (it's "reproduced").

    Compatibility with constraints. Since Koza-I/II only tries 1 time, and then follows this policy, this is compatible with Koza. lil-gp either tries 1 time, or tries forever. Either way, this is compatible with lil-gp. My hacked lil-gp kernel either tries 1 time, n times, or forever. This is compatible as well.

    This pipeline typically produces up to 2 new individuals (the two newly- swapped individuals) per produce(...) call. If the system only needs a single individual, the pipeline will throw one of the new individuals away. The user can also have the pipeline always throw away the second new individual instead of adding it to the population. In this case, the pipeline will only typically produce 1 new individual per produce(...) call.

    Typical Number of Individuals Produced Per produce(...) call
    2 * minimum typical number of individuals produced by each source, unless tossSecondParent is set, in which case it's simply the minimum typical number.

    Number of Sources
    2

    Parameters

    base.tries
    int >= 1    		 (number of times to try finding valid pairs of nodes)
    base.maxdepth
    int >= 1    		 (maximum valid depth of a crossed-over subtree)
    base.maxsize
    int >= 1    		 (maximum valid size, in nodes, of a crossed-over subtree)
    base.tree.0
    0 < int < (num trees in individuals), if exists    		 (first tree for the crossover; if parameter doesn't exist, tree is picked at random)
    base.tree.1
    0 < int < (num trees in individuals), if exists    		 (second tree for the crossover; if parameter doesn't exist, tree is picked at random. This tree must have the same GPTreeConstraints as tree.0, if tree.0 is defined.)
    base.ns.n
    classname, inherits and != GPNodeSelector,
    or String same    		 (GPNodeSelector for parent n (n is 0 or 1) If, for ns.1 the value is same, then ns.1 a copy of whatever ns.0 is. Note that the default version has no n)
    base.toss
    bool = true or false (default)/td>     		(after crossing over with the first new individual, should its second sibling individual be thrown away instead of adding it to the population?)

    Default Base
    gp.koza.xover

    Parameter bases

    base.ns.n
    		nodeselectn (n is 0 or 1)
    See Also:
    Serialized Form

    • Field Detail

      • nodeselect1

        public GPNodeSelector nodeselect1
        How the pipeline selects a node from individual 1

      • nodeselect2

        public GPNodeSelector nodeselect2
        How the pipeline selects a node from individual 2

      • tree1

        public int tree1
        Is the first tree fixed? If not, this is -1

      • tree2

        public int tree2
        Is the second tree fixed? If not, this is -1

      • numTries

        public int numTries
        How many times the pipeline attempts to pick nodes until it gives up.

      • maxDepth

        public int maxDepth
        The deepest tree the pipeline is allowed to form. Single terminal trees are depth 1.

      • maxSize

        public int maxSize
        The largest tree (measured as a nodecount) the pipeline is allowed to form.

      • tossSecondParent

        public boolean tossSecondParent
        Should the pipeline discard the second parent after crossing over?

      • parents

        public GPIndividual[] parents
        Temporary holding place for parents

    • Constructor Detail

      • CrossoverPipeline

        public CrossoverPipeline()

    • Method Detail

      • defaultBase

        public Parameter defaultBase()
        Description copied from interface: Prototype
        Returns the default base for this prototype. This should generally be implemented by building off of the static base() method on the DefaultsForm object for the prototype's package. This should be callable during setup(...).

      • numSources

        public int numSources()
        Description copied from class: BreedingPipeline
        Returns the number of sources to this pipeline. Called during BreedingPipeline's setup. Be sure to return a value > 0, or DYNAMIC_SOURCES which indicates that setup should check the parameter file for the parameter "num-sources" to make its determination.
        Specified by:
        numSources in class BreedingPipeline

      • clone

        public java.lang.Object clone()
        Description copied from interface: Prototype
        Creates a new individual cloned from a prototype, and suitable to begin use in its own evolutionary context.

        Typically this should be a full "deep" clone. However, you may share certain elements with other objects rather than clone hem, depending on the situation:

        • If you hold objects which are shared with other instances, don't clone them.
        • If you hold objects which must be unique, clone them.
        • If you hold objects which were given to you as a gesture of kindness, and aren't owned by you, you probably shouldn't clone them.
        • DON'T attempt to clone: Singletons, Cliques, or Groups.
        • Arrays are not cloned automatically; you may need to clone an array if you're not sharing it with other instances. Arrays have the nice feature of being copyable by calling clone() on them.

        Implementations.

        • If no ancestor of yours implements clone(), and you have no need to do clone deeply, and you are abstract, then you should not declare clone().
        • If no ancestor of yours implements clone(), and you have no need to do clone deeply, and you are not abstract, then you should implement it as follows: 

           public Object clone() 
     {
     try
         { 
         return super.clone();
         }
     catch ((CloneNotSupportedException e)
         { throw new InternalError(); } // never happens
     }
        • If no ancestor of yours implements clone(), but you need to deep-clone some things, then you should implement it as follows: 

           public Object clone() 
     {
     try
         { 
         MyObject myobj = (MyObject) (super.clone());

         // put your deep-cloning code here...
         }
     catch ((CloneNotSupportedException e)
         { throw new InternalError(); } // never happens
     return myobj;
     }
        • If an ancestor has implemented clone(), and you also need to deep clone some things, then you should implement it as follows: 

           public Object clone() 
     { 
     MyObject myobj = (MyObject) (super.clone());

     // put your deep-cloning code here...

     return myobj;
     }
        Specified by:
        clone in interface Prototype
        Overrides:
        clone in class BreedingPipeline

      • setup

        public void setup(EvolutionState state,
                  Parameter base)
        Description copied from class: BreedingSource
        Sets up the BreedingPipeline. You can use state.output.error here because the top-level caller promises to call exitIfErrors() after calling setup. Note that probability might get modified again by an external source if it doesn't normalize right.

        The most common modification is to normalize it with some other set of probabilities, then set all of them up in increasing summation; this allows the use of the fast static BreedingSource-picking utility method, BreedingSource.pickRandom(...). In order to use this method, for example, if four breeding source probabilities are {0.3, 0.2, 0.1, 0.4}, then they should get normalized and summed by the outside owners as: {0.3, 0.5, 0.6, 1.0}.

        Specified by:
        setup in interface Prototype
        Specified by:
        setup in interface Setup
        Overrides:
        setup in class BreedingPipeline
        See Also:
        Prototype.setup(EvolutionState,Parameter)

      • typicalIndsProduced

        public int typicalIndsProduced()
        Returns 2 * minimum number of typical individuals produced by any sources, else 1* minimum number if tossSecondParent is true.
        Overrides:
        typicalIndsProduced in class BreedingPipeline

      • verifyPoints

        public boolean verifyPoints(GPInitializer initializer,
                            GPNode inner1,
                            GPNode inner2)
        Returns true if inner1 can feasibly be swapped into inner2's position.

      • produce

        public int produce(int min,
                   int max,
                   int start,
                   int subpopulation,
                   Individual[] inds,
                   EvolutionState state,
                   int thread)
        Description copied from class: BreedingSource
        Produces n individuals from the given subpopulation and puts them into inds[start...start+n-1], where n = Min(Max(q,min),max), where q is the "typical" number of individuals the BreedingSource produces in one shot, and returns n. max must be >= min, and min must be >= 1. For example, crossover might typically produce two individuals, tournament selection might typically produce a single individual, etc.
        Specified by:
        produce in class BreedingSource
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