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| Keywords: Sissys.png Alternative Code Here I show an alternative code for the solution of the two equations This code does not use the function ode45 so it might be a little easier for someone to understand how the model works code in Matlab <pre> Initialize variables b 0 001; rate of infection g 0 1; rate of recovery i 60; total run time S zeros i 1 ; history of infected over time I zeros i 1 ; history of recovered over time S 1 499; population size - 1 I 1 1; must start with atleast one infected to spread the disease time zeros i 1 ; time history Run model for t 1 i-1 S t+1 -b S t I t +g I t +S t ; I t+1 b S t I t -g I t +I t ; time t+1 time t +1; end Display Results clear g b i t; delete unnecessary variables plot time I 'DisplayName' 'I' 'XDataSource' 'time' 'YDataSource' 'I' ; hold all; plot time S 'DisplayName' 'S' 'XDataSource' 'time' 'YDataSource' 'S' ; hold off; figure gcf </pre> An epidemiological graph for the SIS model S represents the number of susceptibles I the number of infectious people; When recovered people become susceptible again Graph generated using MATLAB code sirsys m program <pre> P 60 N 500 options odeset 'RelTol' 1e-4 'AbsTol' 1e-4 ; beta 0 001; v 0 1; T Y ode45 sissys1 0 P N 1 options beta v ; plot T Y 1 T Y 2 ; plot T Y 1 ' ' T Y 2 ' ' ; </pre> sissys1 m function <pre> function dy sissys1 t y beta v dy zeros 2 1 ; a column vector dy 1 - beta y 1 y 2 +v y 2 ; dy 2 beta y 1 y 2 -v y 2 ; end </pre> See also Image Sirsys-p9 png Epidemics | ||||
