Double-x subscript in Pxx, Signal Process Toolbox document

Hi,

In Signal Processing Toolbox User’s Guide R2011b, 6-5, page 179, http://www.mathworks.com/help/pdf_doc/signal/signal_tb.pdf, I am curious why the document uses double-x in Pxx notation, as well as Rxx.

I think one x or without x might be more appropriate. For example, as the notation in the Wikipedia page http://en.wikipedia.org/wiki/Spectral_density#Power_spectral_density.

Could anyone explain the reason?

Bob

Answer 1

[bym]

I guess to differentiate it from cross power spectrum Pxy

[Bob Li]

I would agree.