BUG: pacf_yw doesn't demean #1138
looking at PR #1018 : demeaned xm is not used
unit test for pacf_yw only uses 1 or 2 decimals.
Aside: Where do the reference numbers come from? looks like matlab but it doesn't say explicitly.
just to clarify: Skipper had added tests for pac_yw comparing to Stata at 8 decimals.