How can I fix the error "Subscript indices must either be real positive integers or logicals. "

I'm trying to plot this differential equations system but I ran into this error. I have no idea to solve this problem however I think the problem is this two code line d1=0.15*sin(5*t(1i)); and d2=0.10*sin(7*t(1i));

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

Beta=3; n=2; s1=1.5;
z1=.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(1i));
d2=0.10*sin(7*t(1i));

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

xdot = zeros(4,1);
xdot(1)=10*(x(2)-x(1))+x(4);
xdot(2)=Beta(li)*x(1)-x(1)*x(3)-x(2)*DF1+d1+fi1;
xdot(3)=x(1)*x(2)-8/3*x(3);
xdot(4)=-x(1)*x(3)+n(li)*x(4)+DF2+d2+fi2;
end
%=====================================================
%***************in main.m****************
x=[0.1 2 3 -3];
t=0:0.02:7;
[T,x] = ode23('func3',[t(li) t(1i+1) t(1i+2)],x);
x=x(2,:);
X=x;
Beta(li+1)=abs(S(1))*abs(x(1));
s1(li+1)=abs(S(1));
z1(li+1)=abs(S(1));
s2(li+1)=abs(S(2));
z2(li+1)=abs(S(2));
n(li+1)=abs(x(4))*abs(S(2));
S1(li+1)=S(1);
S2(li+1)=S(2);
X(li+1,:)=x;
D1(li)=d1;
D2(li)=d2;
li;

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 main (line 12)

[T,x] = ode23('func3',[t(1i+1) t(1i+2)],x);

Answer 1

[Walter Roberson]

u1(1i)=-((Beta(1i)+10)*abs(x(1))+2*abs(x(2))+s1(1i)+z1(1i))*sign(S(1));

Beta(1i) is an attempt to index which does not exist.

MATLAB has absolutely no implied multiplication -- not even in the little pastic dimples left over from when the CDs were manufactured.