传染病模型的作业

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1、.模型4传染病有免疫性——病人治愈后即移出感染系统，称移出者即SIR模型假设1）总人数N不变，病人、健康人和移出者的比例分别为2）病人的日接触率l,日治愈率m,接触数s=l/m建立模型是s（t）+i(t)+r(t)=1需建立s（t）i(t)r(t)M文件：functiony=ill(t,x)a=1;b=0.3;y=[a*x(1)*x(2)-b*x(1),-a*x(1)*x(2)]';在Matlab中输入：ts=0:50;>>x0=[0.02,0.98];>>[t,x]=ode45('ill',ts,x0)t=0...1234567891011121314151617181920212

2、2...23242526272829303132333435363738394041424344...454647484950x=0.02000.98000.03900.95250.07320.90190.12850.81690.20330.69270.27950.54380.33120.39950.34440.28390.32470.20270.28630.14930.24180.11450.19860.0917...0.15990.07670.12720.06650.10040.05930.07870.05430.06140.05070.04780.04800.03710.046

3、00.02870.04450.02230.04340.01720.04260.01330.04190.01030.04150.00790.04110.00610.04080.00470.04060.00360.04040.00280.04030.00220.04020.00170.04010.00130.04000.00100.04000.00080.0400...0.00060.03990.00050.03990.00040.03990.00030.03990.00020.03990.00020.03990.00010.03990.00010.03990.00010.03990.0

4、0010.03990.00000.03980.00000.03980.00000.03980.00000.03980.00000.03980.00000.03980.00000.0398>>plot(t,x(:,1),t,x(:,2)),grid,pause画出图形为：...I(t),s(t)图形>>plot(x(:,2),x(:,1)),grid,...I—s图形（相轨县）结果输出的简明计算结果可以看出，随着t的增加，（s,i）沿轨线自右向左运动。i（t）由初值增长至约t=7时达到最大值，然后减少，t趋于无穷，i趋于0时，是s（t）则单调减少，趋于无穷，趋于0.0398。..