LU XINYI

Dear all: Recently, I want to do the bifurcation analysis of a model in following form: ds/dt=b-ds-beta0(1+beta_1cos2pit)si; di/dt=beta0(1+beta_1cos2pit)si-(gamma+d)i dr/dt=gammai-dr However, when I create the model in Matcont, the system will show the error, which shows that the virable "t" can not be identified. Could someone tell me how to solve the problem? I put both the model and error in the attachement.