Exercise 9.6

Answers

(a): A large offset shouldn’t affect the ’natural axes’ from PCA. They only change the origin of the natural axes, but not the directions. We don’t have to perform centering before PCA.
(b): If one dimension is inflated, this will increase the variance along the dimension and make PCA choose ’natural axes’ along the inflated dimension. We should perform input normalized before doing PCA.
(c): If we do input whitening, the ’natural axes’ for the inputs can be any orthogonal axes. Rotation to any angle won’t reveal that one dimension is more important than another because they are all equalized.
We shouldn’t perform input whitening before doing PCA, because that will equalize all axes for the inputs. PCA won’t be able to find axes that has large variances against other axes.

niuers

2021-12-08 10:23