MATLAB: How to initialize an empty vector/null vector in matlab,

Question

I would like to transfer the u_real(n) value to the u_Q1(n) array. But, when I am trying to compile it is telling me that the variable u_Q1 is undefined. How can I define that variable as empty vector.

u_real=real(u);
v_real=real(v);
temp = 0;
for n = 1:100
  if and(u_real(n)>0,v_real(n)>0)
      if n == temp + 1
          u_real(n) == u_Q1(n);
          v_real(n) == v_Q1(n);
          temp = n;
      else
          d = n-temp;
          u_real(n) == u_Q1(n-d+1);
          v_real(n) == v_Q1(n-d+1);
          temp = n-d+1;
      end
  end
end

Answer 1

u_Q1 = [];