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Tree Evaluation OverviewSeptember 17th, 2013Erik Fredericks

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Overview

• Step-by-step detail of tree evaluation process• Discussion throughout

• Issues in generating trees that fully satisfy all pre/post conditions

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Tree Setup

• Terminals• Objects defined with:

• Starting state• Target condition

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Tree Setup

• Terminals• Objects defined with:

• Starting state• Target condition

• Examples:• Starting state: FLOAT-ARRAY (Source pre-condition)• Target state: INT-ARRAY (Target pre-condition)

• Starting state: INT (Source pre-condition)• Target state: ARRAY-SIZE (Target pre-condition)

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Node Evaluation

• Role transformation• Check if the current node satisfies the target

condition

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Node Evaluation

• Role transformation• Check if the current node satisfies the target

condition• If true

• Increment object fitness by a large amount• Note that condition is satisfied

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Node Evaluation

• Role transformation• Check if the current node satisfies the target

condition• If true

• Increment object fitness by a large amount• Note that condition is satisfied

• Else• If the transformation was valid

• Increment object fitness by a small amount• “We’re heading in the right direction”

• If it was not valid• Decrement object fitness by a decent amount

• If condition was previously satisfied, penalize further as we’re moving away from a correct answer

• Note that condition is currently unsatisfied

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Node Evaluation

• Data transformation• Check that necessary roles are available for

evaluation• GET-HIGH-INDEX requires an array and an array size

• If so, increase object fitness• Otherwise, penalize

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Fitness Calculation

• Fitness values for each terminal object is summed, and the inverse is calculated• EpochX considers 0.0 to be the best fitness

• Software engineering metrics could further be applied here in the future• Reduce size of tree• Complexify tree• Etc.

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

(Start)

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

Convert a float array to an int array• Target role is int array• FLOAT-ARRAY.fitness += 10.0

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

Get the high index of an array• Children are an array and an int• INT.fitness += 10.0

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

Tree is penalized out of existence if 3rd parameter is not a target-

method

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

Convert an int array to a float array• Target role is float array• INT-ARRAY.fitness += 10.0

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

Overall fitness1.0 / (FLOAT-ARRAY.fitness +

INT.fitness + INT-ARRAY.fitness)

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2CHAR

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOATFitness here would simply be

incremented, as a FLOAT2CHAR is a valid transform

CHAR2INT

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

The composition node (always root) looks for (mergeSort):

• 4 conditions to be satisfied• FLOAT-ARRAY -> INT-ARRAY• ARRAY-HIGH-INDEX• TARGET-METHOD• INT-ARRAY -> FLOAT-ARRAY

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An Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

FLOAT2INT

FLOAT-ARRAY

ARR2INDEX

INT-ARRAY

INT2FLOAT

What the results show:

• Generally, 2/3 of the conditions are satisfied (never all 3)

• Evolution finding simplest path, or simplest path with an extra NOP

• (not chaining transforms)

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A Non-Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

CHAR2VOID NOP

INT-ARRAY

INT2FLOAT

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A Non-Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

CHAR2VOID NOP

INT-ARRAY

INT2FLOAT

Penalize for an invalid transform

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A Non-Ideal Tree

WRAPPER

FLOAT-ARRAY INT TARGET-METHOD

CHAR2VOID NOP

INT-ARRAY

INT2FLOAT

Penalize for an unsatisfied condition

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Discussion

• Evaluation methods

• Use of terminals

• Other?