How to correct my s function code ?please help

when I run the simulink of tire model, it always occur :Output returned by S-function 't_dugoff' in 'untitled1/front tire model' during flag=3 call must be a real vector of length 3,

the code is like this:

function [sys,x0,str,ts] = t_dugoff(t,x,u,flag)
switch flag,
case 0,
[sys,x0,str,ts]=mdlInitializeSizes;
 case 3,
sys = mdlOutputs(t,x,u);
case { 1, 2, 4, 9 }
sys=[];
otherwise
error(['Unhandled flag = ',num2str(flag)]);
end
function [sys,x0,str,ts]=mdlInitializeSizes
sizes = simsizes;
sizes.NumContStates = 0;
sizes.NumDiscStates = 0;
sizes.NumOutputs = 3;
sizes.NumInputs = 4;
sizes.DirFeedthrough =1 ;
sizes.NumSampleTimes = 0;
sys = simsizes(sizes);
x0 = [];
str = [];
ts = [];
function sys = mdlOutputs(t,x,u)
wload=u(4);
vspd=u(2);
whlspd=u(1);
slip_A=u(3);
R=0.334;
cx=20000;
cy=16000;
fscl=0.0034;
u0=0.9;
a=slip_A*pi/180;
slip=(vspd-R*whlspd)/vspd;
uf=u0*(1-fscl*vspd*slip);
epslon=1e-6;
MAXF=uf*wload*(1-slip); 
demandF=((cx*slip)^2+(cy*tan(a))^2)^0.5;
lamda=MAXF/2/demandF;
if lamda>=1
    Flf=cx*slip/(1-slip);
    Fyf=cy*tan(a)/(1-slip);

end

if lamda<1

          Flf=cx*slip/(1-slip)*(2-lamda)*lamda;
          Fyf=cy*tan(a)/(1-slip)*(2-lamda)*lamda;

end

sys=[Flf Fyf slip];

[Hadi Abbas]

Do you remember how you solved this problem??

[Walter Roberson]

What happens if lambda equals 1 exactly?. What happens if slip is 1, leading to division by 0?

Answer 1

[Kaustubha Govind]

It looks like this line may not be returning a vector with 3 elements (because you have configured the S-function for 3 outputs) as Simulink expects:

sys=[Flf Fyf slip];

It might be that Flf, Fyf and slip are not scalars, and therefore concatenate to a vector that does not have a size equal to 3.

I would recommend setting a breakpoint at the line. Then run your model again and examine the dimensions of the intermediate variables and of the output 'sys'.