Thursday, July 30, 2009

1-of-K representation

Reference from Machine Learning and Pattern Recognition, Bishop

Section 2.2 P.74
A particularly convenient representation is the 1-of-K scheme in which the variable is represented by a K-dimensional vector x in which one of the elements xk equals 1, and all remaining elements equal 0.

Keyword: 1-of-K, representation

Tuesday, July 21, 2009

Generative model and Discriminative model


簡單的名詞解釋上的區別是
discriminative model 估計的是條件概率分布(conditional distribution, posterior class probabilities)
p(class|observed x)
generative model 估計的是聯合機率分布(joint probability distribution)
p(observed x, class),之所以稱為Generative model,就是因為根據Joint probabilities,利用各種sampling方法,就可以產生人工資料(Synthetic data)。

Christoper M. Bishop, Pattern Recognition and Machine Learning Section 1.5.4, p.43有提到這兩者的區別。在這裡作者Bishop也點出了第三種學習方法,discriminative function.
Sampling方法,可在此書的第11章找到各式方法。

在目前的研究上,
有學者研究綜合兩者的優點的Hybrid方法,
  • Hybrid Generative-Discriminative Models for Speech and Speaker Recognition (2002)
  • Multi-Conditional Learning: Generative/Discriminative Training for Clustering and Classfication(2006)
  • Bias-Variance tradeoff in Hybrid Generative-Discriminative models(2007)
  • A hybrid generative/discriminative approach to text classification with additional information(2007)
  • A mixed generative-discriminative framework for pedestrian classification(2008)
  • Combining Evidence from a Generative and a Discriminative Model in Phoneme Recognition(2008)
也有學者提出透過Discriminative model去學習generative model.
  • Learning Generative Models via Discriminative Approaches(2007)
兩者的比較
  • Generative versus discriminative methods for object recognition(2005)

Monday, July 20, 2009

好用免費軟體 - 7zip

7zip免費且支援很多壓縮格式,缺點是介面不太漂亮,也沒辦法double click打開壓縮檔。

教學網站

Sunday, July 19, 2009

Memo: how to type doubledash "--" and underline "_" in LaTex?

How to type double dash in LaTex?
Sometimes we need to type "--" in LaTex, but the parser of Tex will deal with it into one dash.
If you try "- -" a space in two dash, it is not the same with "--".

So you can try
  • \texttt{ }: I think it is good but the format and size of character should be customized.
  • -{}-: Excellent. Nature!
Reference from

Underline is reserved character of LaTex
The reserved characters are
  • $ : dollar sign
  • & :
  • %
  • #
  • _
  • {
  • }
  • ~
  • ^
  • \
If you want to type them, just add a "\" before them.

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