Comparison of Visualization Approaches in Many-
objective Optimization
Zhenan He
College of Computer Science
Sichuan University
Chengdu, Sichuan, CHINA
zhenan@scu.edu.cn
Gary G. Yen
School of Electrical and Computer Engineering
Oklahoma State University
Stillwater, Oklahoma, USA
gyen@okstate.edu
Abstract—In many-objective optimization, visualization of
population in the high-dimensional objective space provides a
critical understanding of the Pareto front. First, visualization
throughout the evolutionary process can be exploited in
developing effective many-objective evolutionary algorithms.
Furthermore, visualization is a crucial component of multi-
criteria decision making. By directly observing the performance
of each solution, the trade-off between objectives, and
distribution of the approximate front, the decision maker can
easily decide which solution should be chosen from. In this
paper, we make a detailed summary for existing visualization
approaches and group them into five different categories. Then,
three evaluation criteria for visualization approaches are
designed, according to which, five state-of-the-arts are
compared under the created data sets. Experimental results
show that all approaches can satisfy each criterion to some
degree but no one can fully achieve all of these criteria. There is
a need to develop the new approach emphasis on fully satisfy all
criteria simultaneously. Then, based on the comparison results,
two future research directions for visualization approach are
proposed.
Keywords—many-objective optimization; visualization;
decision making;
I. INTRODUCTION
Many-objective Optimization Problems (MaOPs) involve
more than three conflicting objectives to be optimized and
widely exist in real-world applications [1-3]. On the other
hand, Multi-objective Optimization Problems (MOPs) contain
only two or three objectives, the low dimensional objective
space of which can be easily visualized by scatter plot with
each axis represents one objective, providing the information
of location, distribution, and shape for the approximate Pareto
front. However, in MaOPs, due to the curse of dimensionality,
the scatter plot is no longer an available tool in visualization
of a high dimensional objective space [4].
For many-objective optimization, it is strongly required to
visualize population in a high dimensional objective space,
not only for the development of the effective Many-Objective
Evolutionary Algorithms (MaOEAs), but also for
performance evaluation of MaOEAs and decision making.
Therefore, a high quality visualization tool must provide three
types of information in the high dimensional space. First, it
should provide accurate shape, location, and range of the
approximate Pareto front [4]. Second, from it, decision makers
can observe trade-off between objectives, monitor the
evolution progress, assess the quality of the approximate front,
and select their preferred solutions if desired [5]. Third, this
visualization tool itself should be scalable to any dimensions,
handle a large number of individuals on the approximate front,
and simultaneously visualize multiple fronts for the purpose
of visual comparison. Moreover, the resulted visualization
plot should be robust and insensitive to the addition or
removal of an individual.
In the literature, in order to view high dimensional data,
many visualization approaches have been proposed. First,
Buddle chart [6] extends the scatter plot from visualization of
three dimensional space to five dimensional space using size
and color to represent the fourth and fifth dimensions,
respectively. However, it cannot be extended further more. On
the other hand, in a M-dimension objective space, where M is
any integer number, Parallel Coordinates [7] and Heatmaps
[8] represent a M-dimension solution on a two-dimension
parallel coordinate system with M parallel axes representing
M objectives [5]. Then, the original objective values of
solutions can be retained. Borrowing the idea from Physics,
RadViz [9] transforms each solution’s objective value in high
dimensional space to the distance between the solutions and
that objective in the mapped two dimensional space. Sammon
Mapping [10] and Multi-Dimensional Scaling [11] construct
a mapping from a high dimensional objective space into a two-
dimension space by preserving local relations between each
pair of solutions in a high dimensional space. Finally, Self-
Organizing Map [12] and Neuroscale [13] apply surrogate
model to accomplish the mapping from high dimensional
space to lower dimension.
In this paper, we present a summary of existing
visualization approaches in literature and group them into five
different categories. Then, three evaluation criteria are
designed, each of which focuses on how the visualization
method reflects the information of the original front, how the
visualization result is helpful to decision making, and the
characteristics of the visualization approach. According to
these criteria, four state-of-the-arts are compared under four
created data sets. Finally, based on the comparison results, two
future research directions for visualization approach are
proposed. First, ensemble a group of visualization approaches
978-1-5090-4601-0/17/$31.00 ©2017 IEEE
This work was supported in part by the National Nature Science Foundation
of China under grant 61602328, and by the Sichuan University under grant
2082204194216.