文中我们用DA代之domain adaptation,TL代指transfer learning。本人初涉这个领域,若下文心得有误,望各位看官老爷/娘娘海涵。read with caution :)
故事如何讲起呢?
首先明确一个故事背景:我们有Source domain(S)和Target domain(T)这两个东西。
domain这个概念太玄乎了,什么叫domain?
domain就是三个要素的组合:
input space X:也即feature space,xi in X可以理解为是一个描述输入图像的vector;
output space Y:也即label space,在classfication任务中,yi in Y可以是0,1(binary classification)或者(1,2,。。。,K)(multi-class classification)
probability distribution between X and Y:从X映射到Y的联合概率分布(P(x,y))。
此处插播一个很基础的背景知识:
- p(x,y) is joint probability distribution;
- p(x|y) & p(y|x) are conditional probability distribution;
- p(x) & p(y) are marginal probability distribution;
在贝叶斯估计的框架下,这几种概率分布被赋予了新的意义和名字:
- p(x) is the evidence or data distribution;
- p(x|y) is the likelihood;
- p(y|x) is the posterior distribution;后验概率,即在验视feature x之后得到的关于sample的label y的估计&