How could I caculate the symbolic function/equition with summation?

How could I caculate this? Actually, I only want to get the expression function. I want to take derivative of t. But there is s1*l1, I want to simplify this function. I try the 'symsum', however it does not work. Because here is a subscript such as sj.

Thank you for your help

best.

Answer 1

[Walter Roberson]

If you want to take the derivative with respect to t, you can pretty much read that off.

and and and are independent of t, so those become constant multiple for the purpose of differentiation, and the derivative becomes

k(1).^2 .* d(1) - 2/3 .* sum(k(1:100).^2 .* d(1:100));

if k and d are length 100 anyhow then that simplifies to

k(1).^2 .* d(1) - 2/3 .* sum(k.^2 .* d);

Both of these assume that k and d are vectors with the same orientation.

[Ziwei Li]

Thanks a lot