if garch errors have a positive spectral density, which is a positive value? do model with garch errors have spectral density do curves have a positive mass do arg models have positive errors do curve errors have a positive spectral density do arc models have positive spectral density do garch errors have a positive spectral density do arc models have a positive spectral density? what model has positive spectral density? do r models have spectral density do aar models with garch errors have positive spectral density do curve errors bounded which model has positive spectral density what model would have positive gap errors which of the following models would have positive spectral density? do arc models show errors do model uncertainties have a positive spectral density do arithmetic models with garch errors have a positive spectral density do garch error models have spectral density does model with curve error have positive spectral density?