Social distance and Hospitals' capacity are two very important factors in the COVID-19 pandemic, which usually change over time. Nevertheless, studies on forecasting this pandemic have not approximately considered these changes in their models. In this study, we accordingly provided a new nonlinear diffusion model by considering these changes for forecasting the COVID-19 outbreak in Iran. This new model generally indicated that it can well follow and predict the trends of the new cases, new

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... veries and daily deaths relevant to Iran's COVID-19 epidemic. In this model, some outcomes also indicated that this model can detect some-things about the management style of the COVID-19 epidemic in Iran. Therefore, since this model could follow three waves of the COVID-19 outbreak in Iran, it can be used in mitigation strategies for the better management of the COVID-19 epidemic in Iran and even other world countries.