[6152] | 1 | /* |
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| 2 | Copyright 2006 by Sean Luke |
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| 3 | Licensed under the Academic Free License version 3.0 |
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| 4 | See the file "LICENSE" for more information |
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| 5 | */ |
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| 6 | |
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| 7 | |
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| 8 | package ec.gp.build; |
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| 9 | import ec.gp.*; |
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| 10 | import ec.*; |
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| 11 | import ec.util.*; |
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| 12 | |
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| 13 | /* |
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| 14 | * RandomBranch.java |
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| 15 | * |
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| 16 | * Created: Mon Dec 13 14:26:02 1999 |
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| 17 | * By: Sean Luke |
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| 18 | */ |
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| 19 | |
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| 20 | /** |
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| 21 | * RandomBranch implements the <tt>Random_Branch</tt> tree generation |
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| 22 | * method described in |
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| 23 | * |
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| 24 | * <p> Chellapilla, K. 1998. Evolving Modular Programs without Crossover. |
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| 25 | * in <i>Proceedings of the Third Annual Genetic Programming Conference</i> |
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| 26 | * (GP98), J.R. Koza <i>et al</i>, editors. San Fransisco: Morgan Kaufmann. |
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| 27 | * 23--31. |
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| 28 | * |
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| 29 | * <p> This algorithm attempts to create a tree of size <tt>requestedSize</tt>, |
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| 30 | * or "slightly less". |
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| 31 | * |
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| 32 | * If the pipeline does not specify a size it wants (it uses <tt>NOSIZEGIVEN</tt>), |
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| 33 | * the algorithm picks a size at random from either [minSize...maxSize] or from |
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| 34 | * sizeDistribution (one of the two <b>must</b> be defined), and attempts to create |
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| 35 | * a tree of that size or "slightly less". |
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| 36 | * |
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| 37 | * @author Sean Luke |
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| 38 | * @version 1.0 |
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| 39 | */ |
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| 40 | |
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| 41 | public class RandomBranch extends GPNodeBuilder |
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| 42 | { |
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| 43 | public static final String P_RANDOMBRANCH = "random-branch"; |
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| 44 | |
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| 45 | public Parameter defaultBase() |
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| 46 | { |
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| 47 | return GPBuildDefaults.base().push(P_RANDOMBRANCH); |
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| 48 | } |
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| 49 | |
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| 50 | public void setup(final EvolutionState state, final Parameter base) |
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| 51 | { |
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| 52 | super.setup(state,base); |
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| 53 | |
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| 54 | // we use size distributions -- did the user specify any? |
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| 55 | if (!canPick()) |
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| 56 | state.output.fatal("RandomBranch requires some kind of size distribution set, either with " + P_MINSIZE + "/" + P_MAXSIZE + ", or with " + P_NUMSIZES + ".", |
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| 57 | base, defaultBase()); |
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| 58 | } |
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| 59 | |
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| 60 | public GPNode newRootedTree(final EvolutionState state, |
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| 61 | final GPType type, |
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| 62 | final int thread, |
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| 63 | final GPNodeParent parent, |
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| 64 | final GPFunctionSet set, |
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| 65 | final int argposition, |
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| 66 | final int requestedSize) |
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| 67 | { |
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| 68 | if (requestedSize == NOSIZEGIVEN) // pick from the distribution |
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| 69 | return randomBranch(state,type,pickSize(state,thread),thread,parent,argposition,set); |
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| 70 | if (requestedSize < 1) |
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| 71 | state.output.fatal("ec.gp.build.RandomBranch requested to build a tree, but a requested size was given that is < 1."); |
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| 72 | return randomBranch(state,type,requestedSize,thread,parent,argposition,set); |
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| 73 | } |
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| 74 | |
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| 75 | private GPNode randomBranch(final EvolutionState state, |
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| 76 | final GPType type, |
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| 77 | final int maxLength, |
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| 78 | final int thread, |
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| 79 | final GPNodeParent parent, |
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| 80 | final int argposition, |
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| 81 | final GPFunctionSet set) |
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| 82 | { |
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| 83 | // randomBranch can mess up if there are no available terminals for a given type. If this occurs, |
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| 84 | // and we find ourselves unable to pick a terminal when we want to do so, we will issue a warning, |
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| 85 | // and pick a nonterminal, violating the maximum-size contract. This can lead to pathological situations |
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| 86 | // where the system will continue to go on and on unable to stop because it can't pick a terminal, |
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| 87 | // resulting in running out of memory or some such. But there are cases where we'd want to let |
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| 88 | // this work itself out. |
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| 89 | boolean triedTerminals = false; |
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| 90 | |
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| 91 | int t = type.type; |
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| 92 | GPNode[] terminals = set.terminals[t]; |
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| 93 | GPNode[] nonterminals = set.nonterminals[t]; |
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| 94 | GPNode[] nodes = set.nodes[t]; |
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| 95 | |
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| 96 | if (nodes.length == 0) |
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| 97 | errorAboutNoNodeWithType(type, state); // total failure |
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| 98 | |
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| 99 | if (( maxLength == 1 || // if the desired length is 1 |
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| 100 | warnAboutNonterminal(nonterminals.length==0, type, false, state)) && // OR if there are NO nonterminals! |
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| 101 | (triedTerminals = true) && // [first set triedTerminals] |
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| 102 | terminals.length != 0) // AND if there are available terminals |
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| 103 | { |
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| 104 | GPNode n = (GPNode)(terminals[state.random[thread].nextInt(terminals.length)].lightClone()); |
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| 105 | n.resetNode(state,thread); // give ERCs a chance to randomize |
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| 106 | n.argposition = (byte)argposition; |
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| 107 | n.parent = parent; |
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| 108 | return n; |
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| 109 | } |
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| 110 | else |
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| 111 | { |
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| 112 | if (triedTerminals) warnAboutNoTerminalWithType(type, false, state); // we tried terminals and we're here because there were none! |
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| 113 | |
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| 114 | // grab all the nodes whose arity is <= maxlength-1 |
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| 115 | int len = set.nonterminalsUnderArity[type.type].length-1; |
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| 116 | if (len > maxLength-1) len = maxLength-1; |
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| 117 | GPNode[] okayNonterms = set.nonterminalsUnderArity[type.type][len]; |
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| 118 | |
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| 119 | if (okayNonterms.length == 0) // no nodes, pick a terminal |
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| 120 | { |
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| 121 | if (terminals.length == 0) |
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| 122 | errorAboutNoNodeWithType(type, state); // total failure |
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| 123 | |
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| 124 | GPNode n = (GPNode)(terminals[state.random[thread].nextInt(terminals.length)].lightClone()); |
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| 125 | n.resetNode(state,thread); // give ERCs a chance to randomize |
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| 126 | n.argposition = (byte)argposition; |
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| 127 | n.parent = parent; |
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| 128 | return n; |
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| 129 | } |
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| 130 | else // we've got nonterminals, pick one at random |
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| 131 | { |
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| 132 | GPNode n = (GPNode)(okayNonterms[state.random[thread].nextInt(okayNonterms.length)].lightClone()); |
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| 133 | n.resetNode(state,thread); // give ERCs a chance to randomize |
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| 134 | n.argposition = (byte)argposition; |
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| 135 | n.parent = parent; |
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| 136 | |
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| 137 | // Populate the node... |
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| 138 | GPType[] childtypes = n.constraints(((GPInitializer)state.initializer)).childtypes; |
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| 139 | for(int x=0;x<childtypes.length;x++) |
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| 140 | n.children[x] = randomBranch( |
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| 141 | state,childtypes[x], |
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| 142 | (maxLength-1)/childtypes.length, // note int division |
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| 143 | thread,n,x,set); |
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| 144 | return n; |
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| 145 | } |
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| 146 | } |
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| 147 | } |
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| 148 | |
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| 149 | } |
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