function?[tSIR]?=?differentialSIR（NbetagammaMaxTime）
%
%?
%
%?RISK_STRUCTURE（?beta?gamma?S0?I0?MaxTime）
%??????This?is?the?MATLAB?version?of?program?2.1?from?page?19?of?
%?“Modeling?Infectious?Disease?in?humans?and?animals“?
%?by?Keeling?&?Rohani.
%?
%?It?is?the?simple?SIR?epidemic?without?births?or?deaths.%?
%

%?Sets?up?default?parameters?if?necessary.
I0?=?100?/?N;
S0?=?1?-?I0;

%?Checks?all?the?parameters?are?valid
if?S0<=0?
????error（‘Initial?level?of?susceptibles?（%g）?is?less?than?or?equal?to?zero‘S0）;
end

if?I0<=0?
????error（‘Initial?level?of?infecteds?（%g）?is?less?than?or?equal?to?zero‘I0）;
end

if?beta<=0?
????error（‘Transmission?rate?beta?（%g）?is?less?than?or?equal?to?zero‘beta）;
end
????
if?gamma<=0?
????error（‘Recovery?rate?gamma?（%g）?is?less?than?or?equal?to?zero‘gamma）;
end
????
if?MaxTime<=0?
????error（‘Maximum?run?time?（%g）?is?less?than?or?equal?to?zero‘MaxTime）;
end
????
if?S0+I0>1
????warning（‘Initial?level?of?susceptibles+infecteds?（%g+%g=%g）?is?greater?than?one‘S0I0S0+I0）;
end

if?beta????warning（‘Basic?reproductive?ratio?（R_0=%g）?is?less?than?one‘beta/gamma）;
end

S=S0;?I=I0;?R=1-S-I;

%?The?main?iteration?
[t?pop]=ode45（@Diff_2_1[0?MaxTime][S?I?R][][beta?gamma]）;

S=pop（:1）;?I=pop（:2）;?R=pop（:3）;





%?Calculates?the?differential?rates?used?in?the?integration.
function?dPop=Diff_2_1（tpop?parameter）

beta=parameter（1）;?gamma=parameter（2）;
S=pop（1）;?I=pop（2）;?R=pop（3）;

dPop=zeros（31）;

dPop（1）=?-beta*S*I;
dPop（2）=?beta*S*I?-?gamma*I;
dPop（3）=?gamma*I;

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????目錄???????????0??2016-01-19?21:30??YBJAN1916_SIR?model?in?whole?population\
?????文件???????12292??2016-01-22?19:37??YBJAN1916_SIR?model?in?whole?population\.DS_Store
?????目錄???????????0??2016-03-15?21:12??__MACOSX\
?????目錄???????????0??2016-03-15?21:12??__MACOSX\YBJAN1916_SIR?model?in?whole?population\
?????文件?????????120??2016-01-22?19:37??__MACOSX\YBJAN1916_SIR?model?in?whole?population\._.DS_Store
?????目錄???????????0??2016-01-19?21:30??YBJAN1916_SIR?model?in?whole?population\SIR\
?????文件????????1536??2016-01-19?02:31??YBJAN1916_SIR?model?in?whole?population\SIR\differentialSIR.m
?????目錄???????????0??2016-03-15?21:12??__MACOSX\YBJAN1916_SIR?model?in?whole?population\SIR\
?????文件?????????120??2016-01-19?02:31??__MACOSX\YBJAN1916_SIR?model?in?whole?population\SIR\._differentialSIR.m
?????文件????????2361??2016-01-19?02:40??YBJAN1916_SIR?model?in?whole?population\SIR\discreteSIR.m
?????文件?????????171??2016-01-19?02:40??__MACOSX\YBJAN1916_SIR?model?in?whole?population\SIR\._discreteSIR.m
?????文件?????????910??2016-01-19?02:40??YBJAN1916_SIR?model?in?whole?population\SIR\mean_fieldSIR.m
?????文件?????????120??2016-01-19?02:40??__MACOSX\YBJAN1916_SIR?model?in?whole?population\SIR\._mean_fieldSIR.m
?????文件????????1295??2016-01-22?19:38??YBJAN1916_SIR?model?in?whole?population\SIR\SIR.m
?????文件?????????120??2016-01-22?19:38??__MACOSX\YBJAN1916_SIR?model?in?whole?population\SIR\._SIR.m