why does pp.test return linear regression phillips perron test error why does the ppp test return singletonity in regression phillips perron test return single-regression error why phillips perron test fails why does a phillips perron testing return an error why does unit root testing return a singleity why does phillips perron test returns singularities in regression why philip's perron test returns singularities in regression phillips perron test returns why does a philips perron test return a simple regression which function is error when pp test which regression test returns the singletonity which test returns single-variate linear regression? why does the pp.test function return single-point errors why does phantom perron test return summing why philips perron test returns singularities in regression why does pp.test get error why phillips perron function returns a single variable? why does pp test return singularities in regression?