matrix element in summation sign

I have 2 matrix A=[a;b;c] and B=[d;e;f]

Now I want the answer of

So I type the code

syms i

symsum(A(i)*B(i),1,3)

Then there is an error "Indexing input must be numeric, logical or ':'."

But what I mean is A(1)*B(1) + A(2)*B(2) ...

So what is the correct code for this question?

Answer 1

[Mischa Kim]

Lo, use

 syms a b c d e f

 A = [a; b; c];
 B = [d; e; f];

 sum(A.*B)