Opis zjawisk okresowych z monotonicznie zmieniającą się amplitudą

For the purposes of description of economic and natural phenomena with a distinctly outlined trend and a dominating seasonal dependence, the model was proposed. The analytic shape of the trend function f(t), in its general form, is adjusted to the phenomenon being described and subsequently, its parameters are estimated with the average method, using empirical data (t, y1). In such a case, seasonal relations with changing amplitude can sufficiently be described with the model. Model has been employed, with a linear tendency, in our description and forecast of milk purchase in Poland.