Error: "In an assignment A(I) = B, the number of elements in B and I must be the same." error

Hi, I do not know why I running into this error, I hope you guys can help me, please.

%*********in func3.m********
function xdot = func3(t,x)
global DF1 DF2 d1 d2 fi1 fi2 Beta n ii 

Beta=3; n=2; s1=1.5;
z1=0.5; s2=1.8; z2=2;

DF1=0.3*(sin(1*pi*x(1))*sin(2*pi*x(2))*sin(3*pi*x(3))*sin(4*pi*x(4)));
DF2=0.2*(sin(1*pi*x(1))*sin(2*pi*x(2))*sin(3*pi*x(3))*sin(4*pi*x(4)));
d1=0.15*sin(5*t(ii));
d2=0.10*sin(7*t(ii));

u1(ii)=-((Beta+10)*abs(x(1))+2*abs(x(2))+s1(ii)+z1(ii))*sign(s1);
u2(ii)=-(abs(x(1))+(x(1)*x(3))+(0.5+n*abs(x(4))+s2(ii)+z2(ii)))*sign(s2);
fi1=(1.4+0.2*sin(u1(ii)))*u1(ii);
fi2=(1.3+0.2*cos(u2(ii)))*u2(ii);


xdot = zeros(4,1);
xdot(1)= 10*x(2)-10*x(1)+x(4);
xdot(2)= -x(1)*x(3)+Beta*x(1)-x(2)+ DF1+d1+fi1;
xdot(3)=x(1)*x(2) - 8/3*x(3);
xdot(4)=-x(1)*x(3) + n*x(4)+ DF2+d2+fi2;
end
% ====================================================================================
% ********in main.m **********
x=[0.1 2 3 -3];
t=0:0.02:7;
[T,x] = ode23(@func3,[-20 20 ],x);
x=x(2,:);
X=x;

Beta(ii+1)=abs(S(1))*abs(x(1));
s1(ii+1)=abs(S(1));
z1(ii+1)=abs(S(1));
s2(ii+1)=abs(S(2));
z2(ii+1)=abs(S(2));
n(ii+1)=abs(x(4))*abs(S(2));
S1(ii+1)=S(1);
S2(ii+1)=S(2);
X(ii+1,:)=x;
D1(ii)=d1;
D2(ii)=d2;
ii;

figure(3)

plot(t(1:end-1),X)
legend('x_1(t)','x_2(t)','x_3(t)','x_4(t)')
figure(4)
plot(t(1:end-1),S1); hold on
plot(t(1:end-1),S2,'g');
legend('S_1(t)','S_2(t)')
figure(5)
plot(t(1:end-2),u1); hold on
plot(t(1:end-2),u2,'g');
legend('u_1(t)','u_2(t)')

Error:

In an assignment A(I) = B, the number of elements in B and I must be

the same.

Error in func3 (line 22)

xdot(2)= -x(1)*x(3)+Beta*x(1)-x(2)+ DF1+d1+fi1;

Error in odearguments (line 88)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode23 (line 113)

[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn,

...

Error in main (line 11)

[T,x] = ode23(@func3,[-20 20 ],x);

Answer 1

[the cyclist]

You defined the global variable ii, but never assigned it a value. Therefore, it is an empty array.

Therefore d1 is also an empty array, when you assign it.

Therefore this line

xdot(2)= -x(1)*x(3)+Beta*x(1)-x(2)+ DF1+d1+fi1;

has an empty right-hand side, and a non-empty left-hand side, giving the error you see.

I used the debugger to solve this mystery, by stopping the code just before the error occurred. You might want to learn how to use this powerful tool.

[afshin Rezaei]

Thank you, but, what is the best solution to get the respons and fix this error? I used the debugger but I could not fix this.

[the cyclist]

How can I help you? What is the value of ii supposed to be? I have no way of knowing that.