function [sys,x0,str,ts] = sfun_population(t,x,u,flag,r,K,init)

%population dynamics. Rate(r), resources(K) and initial population
%(init) are user inputs.

switch flag,

  case 0,
    [sys,x0,str,ts]=mdlInitializeSizes(init);

  case 1,
    sys=mdlDerivatives(t,x,u);

  case 2,
    sys=mdlUpdate(t,x,u,r,K);

  case 3,
    sys=mdlOutputs(t,x,u);

  case 4,
    sys=mdlGetTimeOfNextVarHit(t,x,u);

  case 9,
    sys=mdlTerminate(t,x,u);

  otherwise
    error(['Unhandled flag = ',num2str(flag)]);

end

function [sys,x0,str,ts]=mdlInitializeSizes(init)

sizes = simsizes;

sizes.NumContStates  = 0;
sizes.NumDiscStates  = 1;
sizes.NumOutputs     = 1;
sizes.NumInputs      = 0;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 1;   % at least one sample time is needed

sys = simsizes(sizes);

%
% initialize the initial conditions
%
x0  = [init];

%
% str is always an empty matrix
%
str = [];

%
% initialize the array of sample times
%
ts  = [1 0];

% end mdlInitializeSizes

%
%=============================================================================
% mdlDerivatives
% Return the derivatives for the continuous states.
%=============================================================================
%
function sys=mdlDerivatives(t,x,u)

sys = [];

% end mdlDerivatives

%
%=============================================================================
% mdlUpdate
% Handle discrete state updates, sample time hits, and major time step
% requirements.
%=============================================================================
%
function sys=mdlUpdate(t,x,u,r,K)

sys = [r*x*(1-x/K)];

% end mdlUpdate

%
%=============================================================================
% mdlOutputs
% Return the block outputs.
%=============================================================================
%
function sys=mdlOutputs(t,x,u)

sys = [x];

% end mdlOutputs

%
%=============================================================================
% mdlGetTimeOfNextVarHit
% Return the time of the next hit for this block.  Note that the result is
% absolute time.  Note that this function is only used when you specify a
% variable discrete-time sample time [-2 0] in the sample time array in
% mdlInitializeSizes.
%=============================================================================
%
function sys=mdlGetTimeOfNextVarHit(t,x,u)

sampleTime = 1;    %  Example, set the next hit to be one second later.
sys = t + sampleTime;

% end mdlGetTimeOfNextVarHit

%
%=============================================================================
% mdlTerminate
% Perform any end of simulation tasks.
%=============================================================================
%
function sys=mdlTerminate(t,x,u)

sys = [];

% end mdlTerminate