ec.gp
Class ERC
java.lang.Object
ec.gp.GPNode
ec.gp.ERC
- All Implemented Interfaces:
- GPNodeParent, Prototype, Setup, java.io.Serializable, java.lang.Cloneable
public abstract class ERC
- extends GPNode
ERC is an abstract GPNode which implements Ephemeral Random Constants,
as described in Koza I. An ERC is a node which, when first instantiated,
gets set to some random constant value which it always returns from
then on, even after being crossed over into other individuals.
In order to implement an ERC, you need to override several methods below.
Impementing an ERC
A basic no-frills ERC needs to have the following things:
- The data holding the ERC (perhaps a float or a couple of floats)
- An implementation of the eval method which returns the appropriate
data when the node is evaluated.
- Possibly an implementation of the clone method to copy that data
properly. If your ERC data is just a simple or immutable type
(like an int or a string), you don't need write a clone() method;
the default one works fine. But if your data is an array or other
mutable object, you'll need to override the clone() method to copy
the array.
- An implementation of the resetNode method to randomize the
data once cloned from the prototype. This essentially "initializes"
your ERC.
- An implementation of the encode method which presents the
ERC as a String. If you don't plan on writing individuals out to
files in a fashion that enables them to be read back in again later,
but only care to print out individuals for statistics purposes,
you can implement this to just
write "" + value, where value is your data.
- An implementation of the nodeEquals method to return true if
the other node is also an ERC of the same type, and it has the
same ERC data as yourself.
A more advanced ERC will need some of the following gizmos:
- If you have ERCs of different class types (for example, a vector ERC
and a floating-point scalar ERC), you will wish to distinguish them
when they're printed to files. To do this, override the name
method to return different strings for each of them (perhaps "vec" versus "").
- If you want to write your ERCs to files such that they can be read
back in again, you'll need to override the encode method
to write using the ec.util.Code class. Further, you'll need to
override the decode method to read in the individual using the
ec.util.Code and ec.util.DecodeReturn classes. The
default version -- which is wrong -- returns false.
When you do this, you'll probably also want to override the toStringForHumans()
method to return a simple string form of the ERC: perhaps just a number
or a vector like "<7.24, 9.23>". This is because by default toStringForHumans()
calls toString(), which in turn calls encode, which you have
just overidden to be more computer-ish.
- ERCs can be mutated using a custom mutator pipeline, for example the
ec.gp.breed.MutateERCPipeline. If you expect to mutate your ERCs,
you may wish to override the mutateERC method to do something
more subtle than its default setting (which just randomizes the
ERC again, by calling resetNode).
- The default nodeHashCode implementation is poor and slow (it
creates a string using encode() and then hashes the sting). You might
create a better (and probably simpler) hash code function.
- If you're going to use facilities such as the Island Model or the distributed
evaluator, you'll need to implement the writeNode and readNode
methods to read/write the node to DataInput/DataOutput. The default implementations
just throw errors.
- If you need to set up your ERC class from the parameter file, do so in the setup method.
See the ec.app.regression.func.RegERC class for an example of a simple but "fuly-implemented"
ERC. A slightly more complicated example can be found in ec.app.lawnmower.func.LawnERC.
- See Also:
- Serialized Form
Fields inherited from class ec.gp.GPNode |
argposition, children, constraints, GPNODEPRINTTAB, MAXPRINTBYTES, NODESEARCH_ALL, NODESEARCH_CUSTOM, NODESEARCH_NONTERMINALS, NODESEARCH_TERMINALS, P_NODE, P_NODECONSTRAINTS, parent, REPLACEMENT_CHAR, SITUATION_MUTATION, SITUATION_NEWIND |
Constructor Summary |
ERC()
|
Method Summary |
void |
checkConstraints(EvolutionState state,
int tree,
GPIndividual typicalIndividual,
Parameter individualBase)
Checks to make certain that the ERC has no children. |
boolean |
decode(DecodeReturn dret)
Decodes data into the ERC from dret. |
abstract java.lang.String |
encode()
Encodes data from the ERC, using ec.util.Code. |
void |
mutateERC(EvolutionState state,
int thread)
Mutates the node's "value". |
java.lang.String |
name()
Returns the lowercase "name" of this ERC function class, some
simple, short name which distinguishes this class from other ERC
function classes you're using. |
abstract boolean |
nodeEquals(GPNode node)
Implement this to do ERC-to-ERC comparisons. |
int |
nodeHashCode()
Implement this to hash ERCs, along with other nodes, in such a way that two
"equal" ERCs will usually hash to the same value. |
GPNode |
readNode(DecodeReturn dret)
Reads the node symbol,
advancing the DecodeReturn to the first character in the string
beyond the node symbol, and returns a new, empty GPNode of the
appropriate class representing that symbol, else null if the
node symbol is not of the correct type for your GPNode class. |
void |
readNode(EvolutionState state,
java.io.DataInput dataInput)
To successfully read from a DataOutput, you must override this to read your specific ERC data in. |
abstract void |
resetNode(EvolutionState state,
int thread)
Remember to override this to randomize your ERC after it has been cloned. |
java.lang.String |
toString()
This defaults to simply ERC_PREFIX + name() + "[" + encode() + "]" |
java.lang.String |
toStringForHumans()
You might want to override this to return a special human-readable version of the erc value; otherwise this defaults to toString(); This should be something that resembles a LISP atom. |
void |
writeNode(EvolutionState state,
java.io.DataOutput dataOutput)
To successfully write to a DataOutput, you must override this to write your specific ERC data out. |
Methods inherited from class ec.gp.GPNode |
atDepth, clone, cloneReplacing, cloneReplacing, cloneReplacing, cloneReplacingAtomic, cloneReplacingAtomic, cloneReplacingNoSubclone, constraints, contains, defaultBase, depth, errorInfo, eval, lightClone, makeCTree, makeLatexTree, nodeEquivalentTo, nodeInPosition, numNodes, numNodes, parentType, printNode, printNode, printNodeForHumans, printRootedTree, printRootedTree, printRootedTreeForHumans, readRootedTree, readRootedTree, replaceWith, rootedTreeEquals, rootedTreeHashCode, rootParent, setup, swapCompatibleWith, toStringForError, verify, writeRootedTree |
Methods inherited from class java.lang.Object |
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
ERC_PREFIX
public static final java.lang.String ERC_PREFIX
- See Also:
- Constant Field Values
ERC
public ERC()
name
public java.lang.String name()
- Returns the lowercase "name" of this ERC function class, some
simple, short name which distinguishes this class from other ERC
function classes you're using. If you have only one ERC function
class, you can just return "" (this is what name() returns by default).
Whatever the name is, it should
generally only have letters, numbers, or hyphens or underscores in it.
No whitespace or other characters.
checkConstraints
public void checkConstraints(EvolutionState state,
int tree,
GPIndividual typicalIndividual,
Parameter individualBase)
- Checks to make certain that the ERC has no children.
- Overrides:
checkConstraints
in class GPNode
resetNode
public abstract void resetNode(EvolutionState state,
int thread)
- Remember to override this to randomize your ERC after it has been cloned. The prototype will not ever receive this method call.
- Overrides:
resetNode
in class GPNode
nodeEquals
public abstract boolean nodeEquals(GPNode node)
- Implement this to do ERC-to-ERC comparisons.
- Overrides:
nodeEquals
in class GPNode
nodeHashCode
public int nodeHashCode()
- Implement this to hash ERCs, along with other nodes, in such a way that two
"equal" ERCs will usually hash to the same value. The default value, which
may not be very good, is a combination of the class hash code and the hash
code of the string returned by encode(). You might make a better hash value.
- Overrides:
nodeHashCode
in class GPNode
toStringForHumans
public java.lang.String toStringForHumans()
- You might want to override this to return a special human-readable version of the erc value; otherwise this defaults to toString(); This should be something that resembles a LISP atom. If a simple number or other object won't suffice, you might use something that begins with ERC_PREFIX + name() + [ + ... + ]
- Overrides:
toStringForHumans
in class GPNode
toString
public java.lang.String toString()
- This defaults to simply ERC_PREFIX + name() + "[" + encode() + "]"
- Specified by:
toString
in class GPNode
encode
public abstract java.lang.String encode()
- Encodes data from the ERC, using ec.util.Code.
decode
public boolean decode(DecodeReturn dret)
- Decodes data into the ERC from dret. Return true if you sucessfully
decoded, false if you didn't. Don't increment dret.pos's value beyond
exactly what was needed to decode your ERC. If you fail to decode,
you should make sure that the position and data in the dret are exactly
as they were originally.
mutateERC
public void mutateERC(EvolutionState state,
int thread)
- Mutates the node's "value". This is called by mutating operators
which specifically mutate the "value" of ERCs, as opposed to
replacing them with whole new ERCs. The default form of this function
simply calls resetNode(state,thread), but you might want to modify
this to do a specialized form of mutation, applying gaussian
noise for example.
writeNode
public void writeNode(EvolutionState state,
java.io.DataOutput dataOutput)
throws java.io.IOException
- To successfully write to a DataOutput, you must override this to write your specific ERC data out. The
default implementation issues a fatal error.
- Overrides:
writeNode
in class GPNode
- Throws:
java.io.IOException
readNode
public void readNode(EvolutionState state,
java.io.DataInput dataInput)
throws java.io.IOException
- To successfully read from a DataOutput, you must override this to read your specific ERC data in. The
default implementation issues a fatal error.
- Overrides:
readNode
in class GPNode
- Throws:
java.io.IOException
readNode
public GPNode readNode(DecodeReturn dret)
- Description copied from class:
GPNode
- Reads the node symbol,
advancing the DecodeReturn to the first character in the string
beyond the node symbol, and returns a new, empty GPNode of the
appropriate class representing that symbol, else null if the
node symbol is not of the correct type for your GPNode class. You may
assume that initial whitespace has been eliminated. Generally should
be case-SENSITIVE, unlike in Lisp. The default
version usually works for "simple" function names, that is, not ERCs
or other stuff where you have to encode the symbol.
- Overrides:
readNode
in class GPNode