function ydot=RHS_SID(t,y)


%  RHS_SID
%
%    define the RHS of the model equations. 
%        variables are 
%  y(1): S, susceptible, uninfected individuals [number]
%  y(2): I, infected individuals [number]
%  y(3): D, dead individuals from the infected population [number]

%   array indexes of variables

nVar=3;iS=1;iI=2;iD=3;

global PAR 

% most rates are 1/day

ydot=zeros(nVar,1);


% EQUATIONS 

% Time changes of susceptable individuals,

ydot(iS)= - PAR.Dinfect * y(iD) * y(iS);

ydot(iI)=  PAR.Dinfect * y(iD) * y(iS)- PAR.Imort * y(iI);

    %   time changes of dead infected individuals
ydot(iD)= PAR.Imort * y(iI)-PAR.Ddecay*y(iD);