具有不確定參數C之模糊支持向量機; Fuzzy Support Vector Machines with the Uncertainty of Parameter C

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题名:	具有不確定參數C之模糊支持向量機;Fuzzy Support Vector Machines with the Uncertainty of Parameter C
作者:	韓明峰;Ming-Feng Han
贡献者:	電機工程研究所
关键词:	模糊理論;支持向量機;不確定性;Fuzzy set;Support Vector Machines;Uncertainty
日期:	2008-07-01
上传时间:	2009-09-22 12:13:42 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	在圖形識別（Pattern Recognition）中，常希望可以在雜亂無章的原始資料裡，設法挖掘出其規律及特徵，進而輔助分類器在決策上的分析。因此，本文研究目的是藉由訓練樣本間的模糊性質採掘出有用的特徵，以改善支持向量機（Support Vector Machines；SVMs）的性能。在理論建構上，本文假設訓練樣本分布為兩個高斯密度函數且具有類重疊（Class Overlap）現象，一個具有模糊性質的類重疊分布可以通過機率密度函數的交集加以確定。因此，對於訓練樣本的模糊歸屬函數(Fuzzy Membership Function)，本文將依據支持向量(Support Vectors)的特性加以建構，例如：落在間隔(Margin)內的訓練樣本即支持向量，一般發生在類重疊中心區域，它們對於決策邊界(decision boundary)的建立，提供較多的貢獻，所以歸屬函數的確定過程中將給予較大的權重。另外，落在間隔外的支持向量，一般發生在較遠離類重疊交點，由於本身是訓練誤差(Training Error)且對於決策邊界的貢獻較少，所以歸屬函數值予以較小的權重。實際中，在支持向量機的目標函數設計上，本文利用歸屬函數與參數C重新定義一個模糊懲罰參數（Fuzzy-penalizing parameter），以每個訓練樣本存有的不同貢獻度去平衡間隔大小與訓練誤差，最後呈現一種新的且有效率的模糊支持向量機（Fuzzy Support Vector Machines；FSVMs）。為了驗證這個分類器，我們從UCI資料庫中解決四個真實世界中的分類問題。實驗1進行與傳統支持向量機的比較，其結果顯示模糊支持向量機有較好的性能且是一個具有價值的分類器。實驗2進行不同歸屬函數的比較，其結果證實本論文呈現的歸屬函數建立法是較可行且較客觀的方法。 In typical pattern recognition applications, there are usually only some vague and general knowledge about the situation. An optimal classifier will be definitely hard to develop if the decision function lacks sufficient knowledge. The aim of our experiments is to extract some features by some appropriate transformation of the training data set. In this thesis, we assume that the training samples are drawn from a Gaussian distribution. We also assume that if the data sets are in an imprecise situation, such as classes overlap. The overlap can be represented by fuzzy sets. Therefore, a fuzzy membership can be created according to the property of class overlap. For example, one can treat the closer training data of decision boundary as Support Vectors (SVs) in the center of classes overlap and let these points have higher degree of the fuzzy membership. That is because these points have higher contribution to the decision boundary. Relatively, one can treat the father training data of the decision boundary as SVs outside the margin and let these points have lower degree of fuzzy membership. In Support Vector Machines (SVMs), we define a fuzzy-penalizing parameter to balance both margin width and model complexity. Finally, a powerful learning classifier is shown. It is the Fuzzy Support Vector Machines with the Uncertainty of Parameter C rule (FSVMs-UPC). In order to verify this classifier, the proposed method is compared with traditional SVM in experiment 1. Results show that the proposed FSVMs-UPC is superior to the traditional SVM in terms of both testing accuracy rate and stability. Experiment 2 shows our membership generation method concentrate on overlapping is a more feasible and better membership.
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