机器学习导论(张志华):渐近性质
前言
這個筆記是北大那位老師課程的學習筆記,講的概念淺顯易懂,非常有利于我們掌握基本的概念,從而掌握相關的技術。
basic concepts
a two-class problem can be assumped as a Bernoulli distribution
Z ̄M(z∣θ,n1+nm)\overline Z ~~ M(z|\theta,n_1+n_m)Z??M(z∣θ,n1?+nm?)
reproducing kernels
1 Cover’s theorem
A complex pattern-classification problem cast in a high-dimensional space nonlincedy is more likely to be linearly seperable than in a low-dimension space.
kernel
Def 1.1 Let x?RPx \subseteq R^Px?RP be a non empty set: A function K:x*x -> R is called a kerne; over x.
Def 1.2A kernel k is called symmetric of k(xi,xj)=k(xj,xi)k(x_i,x_j)=k(x_j,x_i)k(xi?,xj?)=k(xj?,xi?) for any xiandxj?Xx_i and x_j \subseteq Xxi?andxj??X
Def1.3 A symmetric kernel is positive definite if ∑j,k=1nαjαkK(Xi,Xk)≥0\sum_{j,k=1}^n\alpha_j\alpha_kK(X_i,X_k) \geq 0 j,k=1∑n?αj?αk?K(Xi?,Xk?)≥0
for any n?Nn \subset Nn?N and α1,...,αn{{ \alpha_1,...,\alpha_n}}α1?,...,αn?.
we call the symmetric K a conditional.P.D if +
∑j,k=1nαjαkK(Xi,Xk)≥0\sum_{j,k=1}^n\alpha_j\alpha_kK(X_i,X_k) \geq 0 j,k=1∑n?αj?αk?K(Xi?,Xk?)≥0
foralln≥zfor \quad all \quad n \geq z foralln≥z,x1,xk?X{x_1,x_k}\subset Xx1?,xk??X
Def 1.4 if k is C.P.D then we call -k negative definite.
k(xi,xj)≥0k(x_i,x_j) \geq 0 k(xi?,xj?)≥0
?(x,y)=∣∣x?y∣∣22\phi(x,y)=||x-y||^2_2 ?(x,y)=∣∣x?y∣∣22?
總結
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