Grey trend models

First the modeling procedure of time-varying grey dynamic model is introduced on the basis of grey dynamic model theory. Then the relation between the ordinary Gompertz model and time-varying grey dynamic model is discussed, thus one kind of trend model, grey Gompertz model is derived using time-varying grey dynamic model with logarithmic transformation. Similarly, another kind of trend model, grey logistic model is derived with reciprocal transformation. The validity of the modeling methods are verified via two instances comparing with other modeling methods. The new models and methods will enrich the modeling techniques of grey system theory and of trend models.