errors with s-function level 1 in simulink

HFAI

Hi all,

I am modeling a separator model with pressure and water level as 2 variables.
I first made an m-file(hamda.m) with ode23tb, which is working( 4 plots: pressure, water level, flow of liq output and flow of gas output.
then I used an level 1 s-function( gabileh) applying the m-file(hamda.m) I created as fellow
function [sys,x0,str,ts,simStateCompliance] = gabileh(t,x,u,flag,varargin)

% M-File S-Function implementing

QLi = u(1); Qgi = u(2); kv1 = u(3); kv2 = u(4);


switch flag,

%%%%%%%%%%%%%%%%%%
% Initialization %
%%%%%%%%%%%%%%%%%%
case 0,
[sys,x0,str,ts, simStateCompliance] = mdlInitializeSizes(t,x,u,flag);

%%%%%%%%%%%%%%%
% Derivatives %
%%%%%%%%%%%%%%%

case 1,
sys = mdlDerivatives(t,x,u,QLi,Qgi,kv1,kv2);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Update, Output, and Terminate %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
case {2, 4, 9},
sys = []; % do nothing

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

otherwise
DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));
end


%
%====================================================================== =============
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%====================================================================== =============
%
function [sys, x0,str,ts] = mdlInitializeSizes

sizes = simsizes;
sizes.NumContStates = 2;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 4;
sizes.NumInputs = 4;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0 = [];
str = [];
ts = [0 0]; % continuous sample time: [period, offset]

% Specify the block simStateCompliance. The allowed values are:
% 'UnknownSimState', < The default setting; warn and assume DefaultSimState

simStateCompliance = 'UnknownSimState';

% end mdlInitializeSizes

%
%====================================================================== =============
% mdlDerivatives
%
%====================================================================== =============
%
function sys = mdlDerivatives(t,x,u,varargin)

QLi = u(1); Qgi = u(2); kv1 = u(3); kv2 = u(4);

sys = hamda(t,x,u);

% end mdlInitializeSizes

%====================================================================== =======
% mdlOutputs
% Return the output vector for the S-function
%====================================================================== =======
%
function sys = mdlOutputs(t,x,u)
sys =Qgt;
sys =QLt;
sys = x;


% end mdlOutputs


when I used the level-1 s-function in a simulink with 4 inputs and 4 ouputs,
I keep having the same error:

Error in 'seprig/M-file S-Function1' while executing M-File S-function 'gabileh', flag = 0 (initialize), at start of simulation. MATLAB error message:
Attempted to access u(1); index out of bounds because numel(u)=0.

please help, thanks in adavance