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首页论文研究 - 具有多个深度学习者的时间序列预测:从贝叶斯网络中选择
考虑到深度学习的最新发展,验证哪些方法对多元时间序列数据的预测有效已变得越来越重要。 在这项研究中,我们提出了一种使用多个深度学习者与贝叶斯网络相结合的时间序列预测的新方法,其中使用K-means聚类将训练数据划分为聚类。 我们根据贝叶斯信息准则确定了多少个聚类最适合K均值。 根据每个群集,将培训多个深度学习者。 我们使用了三种类型的深度学习器:深度神经网络(DNN),递归神经网络(RNN)和长短期记忆(LSTM)。 朴素的贝叶斯分类器用于确定哪个深度学习者负责预测特定的时间序列。 我们提议的方法将应用于一组金融时间序列数据(日经平均股票价格),以评估所做预测的准确性。 与采用单个深度学习器来获取所有数据的常规方法相比,我们提出的方法证明了F值和准确性得到了提高。
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Journal of Data Analysis and Information Processing, 2017, 5, 115-130
http://www.scirp.org/journal/jdaip
ISSN Online: 2327-7203
ISSN Print: 2327-7211
DOI: 10.4236/jdaip.2017.53009
August 29, 2017
Time Series Forecasting with Multiple Deep
Learners: Selection from a Bayesian Network
Shusuke Kobayashi, Susumu Shirayama
Graduate School of Engineering, the University of Tokyo, Tokyo, Japan
Abstract
Considering the recent developments in deep learning, it has become incre
a-
singly important to verify what methods are valid for the prediction of mult
i-
variate time-series data. In this study, we propose a novel method of time-se
ries
prediction employing multiple deep learners combined with a Bayesian ne
t-
work where training data is divided into clusters using K-
means clustering.
We decided how many clusters are the best for K-
means with the Bayesian
information criteria. Depending on each cluster, the multiple deep learners
are trained. We used three types of deep learners:
deep neural network
(DNN), recurrent neural network (RNN), and long short-
term memory
(LSTM). A naive Bayes classifier is used to determine which deep learner is in
charge of predicting a particular time-series. Our propos
ed method will be
applied to a set of financial time-
series data, the Nikkei Average Stock price,
to assess the accuracy of the predictions made. Compared with the conve
n-
tional method of employing a single deep learner to acquire all the data, it is
demonstrated by our proposed method that F-value and accuracy are i
m-
proved.
Keywords
Time-Series Data, Deep Learning, Bayesian Network, Recurrent Neural
Network, Long Short-Term Memory, Ensemble Learning, K-Means
1. Introduction
Deep learning has been developed to compensate for the shortcomings of pre-
vious neural networks [1] and is well known for its high performance in the
fields of character and image recognition [2]. In addition, deep learning’s influ-
ence is impacting various other fields [3] [4] [5], and its efficiency and accuracy
have been much bolstered by recent research. However, deep learning is subject
to three main drawbacks. For instance, obtaining and generating appropriate
How to cite this paper:
Kobayashi, S
. and
Shirayama
, S. (2017) Time Series
Forecasting
with Multiple Deep Learners: Selection
from a Bayesian Network
.
Journal of Data
Analysis and Information Processing
,
5,
115
-130.
https://doi.org/10.4236/jdaip.2017.53009
Received:
July 10, 2017
Accepted:
August 26, 2017
Published:
August 29, 2017
Copyright © 201
7 by authors and
Scientific
Research Publishing Inc.
This work is licensed
under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access

S. Kobayashi, S. Shirayama
116
training data is problematic, it suffers from excessively long calculation times.
Moreover, parameter selection is also difficult. While researchers are progressing
toward overcoming such issues, according to some reports, dealing with these
problems is difficult except for subjects in which the formation of feature spaces
such as images and sounds are the key to success [6].
However, while it is clear that deep learning is considered to underpin artifi-
cial intelligence and because the brain’s information processing mechanism is
not fully understood, it is possible to develop new learners by imitating what is
known about the information processing mechanisms of the brain. One way to
develop new learners is to use a Bayesian network [7]. Moreover, it is also con-
ceivable to combine multiple deep learners to create a single new learner. For ex-
ample, ensemble learning and complementary learning are representative learning
methods using multiple learners [8] [9] [10]. In addition, to realize a hierarchical
control mechanism, there are cases where multiple learners are used.
In this research, we develop a new learner using multiple deep learners in
combination with Bayesian networks as the selection method to choose the most
suitable type of learner for each set of test data.
In time-series data prediction with deep learning, overly long calculation times
are required for training. Moreover, a deep learner does not converge due to the
randomness of the time-series data. There is also an issue with employing a Baye-
sian network. In this paper, we try to reduce the computation time and improve
convergence by dividing training data into specific clusters using the K-means
method and creating multiple deep learners from the learning derived from the
divided training data. We also simplify the problem of ambiguity by using a Baye-
sian network to select a suitable deep learner for the task of prediction.
To demonstrate our model, we use a real-life application: predicting the Nik-
kei Average Stock price by taking into consideration the influence of multiple
stock markets. Specifically, we estimate the Nikkei Stock Average of the current
term based on the Nikkei Stock Average of the previous term as well as overseas
major stock price indicators such as NY Dow and FTSE 100. We evaluate the va-
lidity of our proposed method based on the accuracy of the estimation results.
2. Related Works
In this section, we introduce the related works of multiple learners.
In ensemble learning, outputs from each learner are integrated by weighted
averaging or a voting method [8]. In complementary learning, each learner is
combined with the group to compensate for each other’s disadvantages. Com-
plementary learning is a concept arising from the role sharing in the memory
mechanism of the hippocampus and cortex [9]. These learning methods tend to
mainly use weak learners. Conversely, to realize a hierarchical control mechan-
ism, there are cases where multiple learners are used. When the behavior of a
robot or multi-agent entity is controlled, a hierarchical control mechanism is of-
ten adopted as attention is paid to the fact that such task can be divided into
subtasks. Takahashi and Asada have proposed a robot behavior-acquisition me-

S. Kobayashi, S. Shirayama
117
thod by hierarchically constructing multiple learners of the same structure [10]. A
lower-level learner is responsible for different subtasks and learns low-level ac-
tions. A higher-level learner learns higher-level actions by exploiting a lower-level
learner’s knowledge.
Our proposed method, which will be described later, is based on the same
notion as the bagging method used in ensemble learning where training data
are divided and independently learned. The difference between our proposed
method and the bagging method is the division method, the integration of
multiple learners (the method of selecting suitable learners for each set of test
data) to improve learners’ accuracies in their acquisition of the material.
Therefore, similar to Takahashi and Asada [10], we do not hold to the premise
that tasks can be divided into subtasks. Our learner selection method is differ-
ent. However, our use of deep learning entities as learners is different to Ta-
kahashi and Asada’s approach as they simply used learners, which is a
Q-learning algorithm extended to a continuous state behavior space. Further-
more, prior research of learning methods has not fully established a method of
dividing training data, a method of integrating multiple learners, or a method
of hierarchizing learners. In addition, it has also failed to improve each learn-
er’s performance after learning.
3. Proposed Method
As we mentioned, because the information processing mechanism of the brain is
not fully understood, it is possible to develop new learners by imitating the in-
formation processing mechanism of the brain. In this research, we hypothesize
that the brain forms multiple learners in the initial stage of learning and im-
proves the performance of each learner in subsequent learning while selecting a
suitable learner.
To design learners based on this hypothesis, it is necessary to find ways of
constructing multiple learners, selecting a suitable learner, and improving the
accuracy of each learner by using feedback from a particular selected learner.
Hence, we assume that multiple learners have the same structure. The learners
are constructed by the clustering of input data. Selection of a suitable learner is
conducted with a naive Bayes classifier that forms the simplest Bayesian net-
work. Furthermore, after fixing learners, we construct a Bayesian network and
predict outcomes without changing the Bayesian network’s construction. How-
ever, it is preferable to improve each learner’s performance and the Bayesian
network by using feedback gained from the selected learners. This will form one
of our future research topics.
In the next section, we propose a method of constructing a single, unified
learner by using multiple deep learners. Moreover, in Section 3.2, we propose a
method of selecting a suitable learner with a naive Bayes classifier.
3.1. Learning with Multiple Deep Learners
In the analysis of time-series data with a deep learner, the prediction accuracy is

S. Kobayashi, S. Shirayama
118
uneven because the loss function of certain time-series data does not converge. It
is commonly assumed that the learning of weight parameters does not work due
to the non-stationary nature of the data. This problem often occurs when mul-
tiple time-series data are used as training data. In addition, the long computa-
tional times that are required is also an issue.
To solve these problems, we think it is effective to apply clustering methods,
such as K-means, SOM, and SVM, to training data; creating clusters; and con-
structing learners for each cluster. This is because training data divided into
some clusters and multiple learners constructed for each cluster enables us to
extract better patterns and improve convergence of the loss function compared
to constructing a single classifier from all the training data. This method also
enables the reduction of the computational time required. Moreover, classifiers
for selecting a suitable learner are constructed from clustering the results of
training data. This classifier achieves the task of associating test data to a suitable
learner.
Figure 1 shows the framework of learning with multiple deep learners. We
divided the training data into
k
classes (C
1
, ∙∙∙, C
k
) and constructed
k
deep learn-
ers for each class.
Figure 2 shows the framework of this prediction along with
the test data. To determine which deep learner is in charge of prediction, we
constructed a classifier for test data based on the clustering results of the training
data. In this paper, we use K-means as a clustering method. Training data was
divided into clusters with K-means and for each cluster,
k
learners were con-
structed. However, it is necessary to determine the number of clusters in ad-
Figure 1. Multiple deep learner’s structure.
Figure 2. Prediction with multiple learners.
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