visualising multi-objective populations with treemaps
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Visualising Multi-objective Populationswith Treemaps
David WalkerCollege of Engineering, Mathematics and Physical Sciences
University of Exeter, UK
VizGEC 2015
VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Multi-objective Visualisation
Visualising multi-objective populations is an importantaspect of EC
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Treemaps
Visualise hierarchical data (often used for clustering)
Each node has an associated “value”
The value of a node is represented by the amount of spaceassigned to that node in the treemap
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Goal:
Represent a multi-objectivepopulation using a treemap
VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Multi-objective Trees
Step 1: Pareto sortingConstruct a partial ordering of individuals using Pareto sorting– this results in a graph
Step 2: Prune edges using dominance distanceRemove edges such that each node has exactly one parent node(retain the parent with the smallest dominance distance) andinsert an artificial “root” node using the global best
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Multi-objective Treemaps
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
An Example: DTLZ2
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Enhancing the Treemap
Order the nodes to enhance the clarity of the treemap
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Many-objective Treemaps: 3- and 5-objective DTLZ2
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Circular Treemaps
In the treemaps presented so far it is difficult to observedominance relationships – instead use circular treemaps
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Many-objective Circular Treemaps
3-objective DTLZ2
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5-objective DTLZ2
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Revealing Additional Information
Visualising Crowding Distance – as used in NSGA-II
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Visualising Objectives
Hughes defined a many-objective radar design problemcomprising 9 objectives, which group into three categories:
1 range objectives
2 velocity objectives
3 transmission time
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Summary
Treemaps provide a useful 2-dimensional way of visualisinghierarchical data arising within evolutionary computation
Multi- and many-objective populations
Objectives
Highly scalable
Highly flexible – ordering, colouring and node size can bedefined to suit a particular application
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VisualisingMulti-
objectivePopulations
with Treemaps
David Walker
Future Work
Expand the range of applications within evolutionarycomputation (genetic programming solutions)
Further refine the treemap layout algorithms to suit theuse of treemaps within evolutionary computation
Identify other means of constructing trees to representmulti-objective populations that are not adversely affectedby treemaps
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