is the arma curve stationary is arma-garch stationary is a financial series usually stationary what is the station of an arma gardch which model requires stationarity is the arma curve stationary if financial series are stable, is stationarity required? are financial time series stationary are financial time series usually stationary is arma a stationary model do financial time series need to be stationary what model should a time series be does arma-garch require stationary period does the arman curve require stationarity are financial time series stationary or non-stationary is the financial time series usually stationary is arma curve stationary do financial series need stationarily what is the stationality requirement on the arma model does arma curve require stationary