function [sys,x0,str,ts] = s_md(t,x,u,flag,K,tank)
global xinit
if ~isstruct(xinit)
    disp('Run initialize.m before simulating')
    return
end

switch flag
    

  %%%%%%%%%%%%%%%%%%
  % Initialization %
  %%%%%%%%%%%%%%%%%%
  case 0,

    [sys,x0,str,ts]=Initialize(tank);


  %%%%%%%%%%%%%%%
  % Derivatives %
  %%%%%%%%%%%%%%%
  case 1,
   
  sys=md(x,u,K,'derivatives');

  %%%%%%%%%%
  % Update %
  %%%%%%%%%%
  case 2,
    % sys=mdlUpdate(t,x,u);

  %%%%%%%%%%%
  % Outputs %
  %%%%%%%%%%%
case 3,

    
   sys=md(x,u,K,'measurement');
    
    
  %%%%%%%%%%%%%%%%%%%%%%%
  % GetTimeOfNextVarHit %
  %%%%%%%%%%%%%%%%%%%%%%%
  case 4,
    % sys=mdlGetTimeOfNextVarHit(t,x,u);

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

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

end

% end sfuntmpl

%
%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
%

function [sys,x0,str,ts]=Initialize(tank)

%
% call simsizes for a sizes structure, fill it in and convert it to a
% sizes array.
%
% Note that in this example, the values are hard coded.  This is not a
% recommended practice as the characteristics of the block are typically
% defined by the S-function parameters.
%
global xinit streams
sizes = simsizes;

sizes.NumContStates  = 2 ;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 3;
sizes.NumInputs      = getfield(streams,tank)*2;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 1;   % at least one sample time is needed

sys = simsizes(sizes);

%
% initialize the initial conditions
%
x0=getfield(xinit,tank);
%
% str is always an empty matrix
%
str = [];

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



