MATLAB: Symbolic array summation in MATLAB

Question

I am trying to output the following symbolic expression in MATLAB: How can I genereate this?

10*L(1) + 20*L(2) + 30*L(3) + 10*L(4) + 20*L(5) + 30*L(6) + 10*L(7) + 20*L(8) + 30*L(9);

This is my code:

syms J L(k) k

F = J*L(k)

for p = 1:3

P = [10 20 30]';

fff=subs(F,J,P(p))

ss=symsum(fff,k,1,9)

end

The outputted answers are:

10*L(1) + 10*L(2) + 10*L(3) + 10*L(4) + 10*L(5) + 10*L(6) + 10*L(7) + 10*L(8) + 10*L(9)

20*L(1) + 20*L(2) + 20*L(3) + 20*L(4) + 20*L(5) + 20*L(6) + 20*L(7) + 20*L(8) + 20*L(9)

30*L(1) + 30*L(2) + 30*L(3) + 30*L(4) + 30*L(5) + 30*L(6) + 30*L(7) + 30*L(8) + 30*L(9)

Answer 1

Each iteration of the for loop in the above code creates a new symbolic function "ss" which creates three different expressions. Also, in each iteration of the loop, since the value of “p” is constant, “J” is substituted by the same value.

You may use the following code instead to implement the summation

clear; 
syms L(k) 
P = repmat([10 20 30],1,3); 
ss(k) = sum(P.*subs(L(k),k,1:9)); 

Hope this helps!!