Something wrong with a S-funciton code

I writed a S-funciton program as follows:

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

switch flag,

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

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

case 3, sys=mdlOutputs(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 = 20;

sizes.NumOutputs = 20;

sizes.NumInputs = 3;

sizes.DirFeedthrough = 1;

sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0 = [0.3 -2 0.3 -1 0.3 0 0.3 1 0.3 2 0.08 0 0.08 0.25 0.08 0.5 0.08 0.75 0.08 1];

str = [];

ts = [-1 0];

function sys=mdlUpdate(t,x,u,B)

ux(1)=(2*u(1) - 2*x(1))/(2*x(2))^2；

ux(2)=(2*u(2) - 2*x(2))/(2*x(3))^2；

ux(3)=(2*u(3) - 2*x(3))/(2*x(4))^2；

ux(4)=(2*u(4) - 2*x(4))/(2*x(5))^2；

ux(5)=(2*u(5) - 2*x(5))/(2*x(6))^2；

ux(6)=(2*u(6) - 2*x(6))/(2*x(7))^2；

ux(7)=(2*u(7) - 2*x(7))/(2*x(8))^2；

ux(8)=(2*u(8) - 2*x(8))/(2*x(9))^2；

ux(9)=(2*u(9) - 2*x(9))/(2*x(10))^2；

ux(10)=(2*u(10) - 2*x(10))/(2*x(11))^2；

ux(11)=(2*u(11) - 2*x(11))/(2*x(12))^2；

ux(12)=(2*u(12) - 2*x(2))/(2*x(13))^2；

ux(13)=(2*u(13) - 2*x(13))/(2*x(14))^2；

ux(14)=(2*u(14) - 2*x(4))/(2*x(15))^2；

ux(15)=(2*u(15) - 2*x(15))/(2*x(16))^2；

ux(16)=(2*u(16) - 2*x(16))/(2*x(17))^2；

ux(17)=(2*u(17) - 2*x(17))/(2*x(18))^2；

ux(18)=(2*u(18) - 2*x(18))/(2*x(19))^2；

ux(19)=(2*u(19) - 2*x(19))/(2*x(20))^2；

ux(20)=(2*u(20) - 2*x(20))/(2*x(1))^2；

x(1)=x(1)+B*u(3)*ux(1);

x(2)=x(2)+B*u(3)*ux(2);

x(3)=x(3)+B*u(3)*ux(3);

x(4)=x(4)+B*u(3)*ux(4);

x(5)=x(5)+B*u(3)*ux(5);

x(6)=x(6)+B*u(3)*ux(6);

x(7)=x(7)+B*u(3)*ux(7);

x(8)=x(8)+B*u(3)*ux(8);

x(9)=x(9)+B*u(3)*ux(9);

x(10)=x(10)+B*u(3)*ux(10);

x(11)=x(11)+B*u(3)*ux(11);

x(12)=x(12)+B*u(3)*ux(12);

x(13)=x(13)+B*u(3)*ux(13);

x(14)=x(14)+B*u(3)*ux(14);

x(15)=x(15)+B*u(3)*ux(15);

x(16)=x(16)+B*u(3)*ux(16);

x(17)=x(17)+B*u(3)*ux(17);

x(18)=x(18)+B*u(3)*ux(18);

x(19)=x(19)+B*u(3)*ux(19);

x(20)=x(20)+B*u(3)*ux(20);

sys = [x(1);x(2);x(3);x(4);x(5);x(6);x(7);x(8);x(9);x(10);x(11);x(12);x(13);x(14);x(15);x(16);x(17);x(18);x(19);x(20)];

function sys=mdlOutputs(t,x,u)

sys =[x(1);x(2);x(3);x(4);x(5);x(6);x(7);x(8);x(9);x(10);x(11);x(12);x(13);x(14);x(15);x(16);x(17);x(18);x(19);x(20)];

end

But when I run this code in Matlab/Simulink, there was an error: Output returned by S-function 'f' in 'test/F' during flag=3 call must be a real vector of length 20.

I want to know that the length of the output is 20, why is it not right?

[Kaustubha Govind]

Are the values all real (and not complex) as well? You may to set a breakpoint in the mdlOutputs and see what value is returned in 'sys' at the time that the error occurs.

[autshy]

Tnank you for your answering,there are four values NaN,then I changed them and now this code can run .

[febina sam]

can u explain further more clear ,please