PCA no stretching?

[dh44hello]

HI LazyProgrammer,

In your "Statistical Factor Models and Unsupervised Machine Learning" lectures, you mention that PCA transformations should not stretch; they should only rotate.
I was hoping to understand the reason for that, if you could elaborate a little bit.

(I tried posting this question on the Financial Engineering forum, but there, it says "you cannot post in this forum."

Thanks

[lazyprogrammer]

Thanks for your inquiry.

The reason is purely mathematical. If you want to learn the actual details of PCA, I'd recommend looking at the course "Unsupervised Deep Learning in Python" where this is discussed in detail.

In the Finance course the section on PCA is only meant to look at the main high-level points.

And thanks for letting me know about the inability to post; I believe that is fixed now.

[dh44hello]

Will do. Thanks, LazyProgrammer.