How to make a summation using heaviside function?

Hi, May I ask how to make a summation using heaviside function?

Here is my code:

t = 0;
i_q = -[0.01 0.04 0.02 0.06 0.06];                 % Rainfall intensity 
T_q = [100 400 1000 1300 1500];                    % Duration
n = length(i_q);
syms n k
q_aux = @(t)(i_q(k).*(heaviside(t-T_q(k-1))-heaviside(t-T_q(k))));     %%%% k>1       
q = symsum(q_aux,k,2,n)+ @(t) (i_q(1).*(heaviside(t)-heaviside(t-T_q(1))));

Now the code is not working, Could you please tell me how to fix it?

Thank you very much!