MATLAB: Problem with taking Differentiate from variable with counter !

Answer 1

Well, the approach would be as follows:

n=30;
x=sym(zeros(1,n));%preallocation
syms t
for i=1:n
   x(i)=str2sym(sprintf('x%d(t)',i));
end

Now, you can easily take derivative of x as

 diff(x,t)

and observe the result you want.