function ydot=RHS_SI(t,y)


%  RHScovi
%
%    define the RHS of the model equations. 
%        variables are 
%  y(1): S, susceptible, uninfected individuals [number]
%  y(2): I, infected individuals [number]

%   array indexes of variables

nVar=2;iS=1;iI=2;

global PAR 

% most rates are 1/day

ydot=zeros(nVar,1);


% EQUATIONS 

% Time changes of susceptable individuals,

ydot(iS)= - PAR.Iinfect * y(iI) * y(iS);


% Time changes of susceptable individuals,

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