Figure 3

The dynamic process of system (16) with the connections \(\sigma (t)=0.012 t\) and \(\rho (t)=0.12(t+1)\) for Spain data. Meanwhile for Italy data, which is rapidly increasing, we use \(\sigma (t)=0.026 t\) and \(\rho (t)=0.26(t+1)\). China data in March have a stable distribution, therefore we suggest \(\nu =\mu =0.25\) with \(\sigma (t)=80+0.033 t\) and \(\rho (t)=0.34 t+80 \). Finally, for the USA, the graph shows high conformation, thus we utilize exponential connections