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Towards diverse perspective learning with select over multiple temporal poolings = 다양한 관점 학습을 위한 선택적 시계열 풀링 연구
서명 / 저자 Towards diverse perspective learning with select over multiple temporal poolings = 다양한 관점 학습을 위한 선택적 시계열 풀링 연구 / Jihyeon Seong.
발행사항 [대전 : 한국과학기술원, 2023].
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In Time Series Classification (TSC), in order to address the issue of losing temporal information caused by global pooling, temporal pooling methods that consider sequential information have been proposed. However, we found that each temporal pooling has a distinct mechanism, and can perform better depending on time series data. In this paper, we propose a novel temporal pooling method with diverse perspective learning: Select over Multiple Temporal Pooling (SoM-TP). SoM-TP dynamically selects the optimal temporal pooling among multiple methods for each data by attention. The dynamic pooling selection is motivated by the ensemble concept of Multiple Choice Learning (MCL) which selects the best among multiple outputs. To achieve non-iterative optimization, we define a perspective loss. The loss works as a regularizer to reflect all the pooling perspectives. Our massive case study using Layer-wise Relevance Propagation (LRP) reveals the limitation of a single perspective that each temporal pooling has, and ultimately demonstrates the necessity of diverse perspectives achieved by SoM-TP. Extensive experiments are done with the UCR/UEA repository and large datasets.

시계열 분류(TSC)에서는 global pooling이 시간적 정보를 잃는 문제를 해결하기 위해, 연속적인 정보를 고려하는 temporal pooling 방법들이 제안되었다. 그러나 각각의 temporal pooling은 고유한 메커니즘을 가지고 있으며, 시계열 데이터 특성에 따라 성능이 달라질 수 있다. 본 논문에서는 다양한 관점 학습을 위한 새로운 temporal pooling 방법인 선택적 시계열 풀링 방법론(SoM-TP)을 제안한다. SoM-TP는 데이터마다 다중 pooling 방법 중에서 최적의 temporal pooling을 attention을 통해 동적으로 선택한다. 이 동적 풀링 선택은 다중 출력 중에서 최적을 선택을 하는 Multiple Choice Learning (MCL)의 앙상블 개념에서 영감을 받았다. 비반복적인 최적화를 달성하기 위해, 우리는 ``관점 손실 (perspective loss)"을 정의한다. 이 손실은 모든 pooling 관점을 반영하기 위한 정규화 역할을 수행한다. 본 연구는 Layer-wise Relevance Propagation (LRP)를 사용한 대규모 사례 연구를 통해 각 temporal pooling이 가지는 단일 관점의 한계를 드러내고, SoM-TP에 의해 달성되는 다양한 관점의 필요성을 근본적으로 입증하였다. 실험은 UCR/UEA 저장소와 대규모 데이터셋을 활용하여 광범위하게 수행되었다.

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언어 영어
일반주기 저자명의 한글표기 : 성지현
지도교수의 영문표기 : Jaesik Choi
지도교수의 한글표기 : 최재식
Including appendix
학위논문 학위논문(석사) - 한국과학기술원 : 김재철AI대학원,
서지주기 References : p. 17-21
주제 Time series classification
Temporal pooling
Diverse perspective learning
Selection ensemble
시계열 분류
시계열 풀링
다중 관점
선택적 앙상블
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SoM-TP architecture. An aggregated output ofall pooling P is passed to the attention block to calculate the attention score A. In the attention block, a weighted pooling output M is formed by multiplication ofP and a learnable weight vector Ao. After M passes through the convolutional layer 00, the attention score A is drawn out as an encoded weight vector. By an index ofthe highest attention scor

Detailed experimental settings.

Temporal Pooling Performances. The best performances that SoM-TP beat others bolded and the best performances of other temporal poolings are underlined.

Table presents a comparison of models that leverage temporal information, models that exploit scale-invariant properties, and SoM-TP. Firstly, in comparison to state-of-the-art models utilizing temporal information, SoM-TP exhibited the highest performance. Furthermore, when compared to scale-invariant models, SoM-TP consistently outperformed them in terms of overall performance for univariate dat

Comparison ofInput attribution results between fixed and diverse perspective learning. Thefigure results are from three different datasets in the UCR repository; CricketZ, Fungi, and WordSynonyms by each respective row in order. The accuracy results are highly dependent on which pooling 1S used and each pooling shows different attributions result with different perspectives Note that the circles a

Decision boundary of temporal poolings on ToeSegmentationl dataset in UCR repository. To clarify that SoM-TP is a novel classification pooling method, we examine whether pooled vectors of SoM-TP are better clustered than the other temporal poolings. We use t-SNE [54 to investigate decision boundaries. While other temporal pooling vectors are not clearly clustered by classes, SoM-TP's decision boun

Ensemble performance on FCN-MAX.

The \ ablation study for SoM-TP. I is the decay value of the perspective loss, which is one of the most important hyper-parameter in SoM-TP. The ablation study is done with X along the range of [1, 1e-5] with 11 intervals. The blue and red line represents the used pooling operation type, respectively MAX and AVG. And the optimal x with the highest performance is circled in green.

Convolutional stack architecture. We use FCN and ResNet which are specially designed for TSC [57]. Here, the embedding dimensions of each convolutional layer before the pooling and FC layers for the classification decision are drawn.

Performance graph on UCR and UEA by accuracy; FCN and ResNet architec- tures with MAX type pooling. The area under the diagonal line has more datasets, which means SoM-TP is better than the other poolings. However, high pooling complexity resulting from selection- ensemble leads to performance degradation in a few simple TSC datasets. Black dots are independent datasets in the repository and the X

Pooling classification model architecture. The input attribution of best tempora. pooling by fixed-perspective learning is first calculated with LRP: 2+ rule for[이 and 6rule forf11+1:12 Then multivariate input with raw time series and input attribution goes through the model to classify the best pooling methods for each dataset. In this network, the simple global pooling layer is used.

Attention analysis. DPL attention plays a critical role on SoM-TP by selecting appro- priate pooling on each data type. Thefigure shows how DPL attention is trained and formulated: Adiac and OSULeafin UCR repository. First, to consider dataset characteristics, attention weight Ao cumu- latively trained by every batch. We can see that Ao highlights the important feature in one temporal pooling alon

SoM-TP on different time lengths and data sizes. With different datasets which contain different data sizes and time lengths, the SoM-TP works robustly and dynamically selects appro- priate pooling both duringtraining and inference procedures. With the first column, the x-axis, we can see the different time lengths ofeach dataset. Also, with the same 20 epoch and 8 batch size, the batch number is

SoM-TP on different time lengths, data sizes, and dimensions. With different datasets which contain different dimensions in the UEA repository, the SoM-TP works robustly and dynamically selects appropriate pooling both at training and inference procedures. Here, the multivariate datasets with different dimensions and data sizes are shown and the detailed selection of pooling by each data with SoM-

ECG and EEG samples. First, ECG is univariate time series data with 5 classes as shown in (a) with the x-axis oftime and the y-axis of values. Second, EEG is multivariate time series data with 2 classes, non-alcoholic VS alcoholic, as shown in (b) with the x-axis of64 channels and the y-axis of values.

Detailed data description and experimental settings.

Model performances. The best performance of SoM-TP is bolded and the best perfor mances ofother temporal poolings are underlined.