How to fix up my s function?

function [sys,x0,str,ts,simStateCompliance] = fcnuav_1d_sfun(t,x,u,flag)

switch flag,

    case 0,
      [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes;

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

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

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

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

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

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

end

function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes
sizes = simsizes;

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

sys = simsizes(sizes);

x0  = [];
str = [];
ts  = [0 0];

simStateCompliance = 'UnknownSimState';

function sys=mdlDerivatives(t,x,u)
sys = [];

function sys=mdlUpdate(t,x,u)
sys = [];

function sys=mdlOutputs(t,x,u)
m = 0.18;
g = 9.81;
kp = 18;
kd = 175;

zdot2_des = 0;
e = u;
U = m*(zdot2_des+kp*e(2)+kd*e(1)+g);
sys = [U];

function sys=mdlGetTimeOfNextVarHit(t,x,u)
sampleTime = 1;    
sys = t + sampleTime;

function sys=mdlTerminate(t,x,u)
sys = [];

[Walter Roberson]

We might be able to suggest a dating site for lonely functions, but I think it would probably be even better if you described the difficulty you are encountering with the code including any error message.