Error when calling function, "Invalid expression..."

I am trying to write a code to perform Gauss Elimination on any [nxn] sized matrix, but am having trouble with my back substitution after getting my matrix into row echelon form. I keep getting the error, "Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters." on line 35 (the line with the symsum function). I am not familiar with Matlab at all, and so also do not know how to get the output of my function. Any help would be appreciated!

function X = GaussElim(A,b)

[m,n] = size(A)
aug = [A,b]

for k = 1:n+1
    m = k
    for j = k+1:n
        if abs(aug(m,k)) < abs(aug(j,k))
            m = j
        end
        if aug(m,k) == 0
            fprintf('No unique solution exists.')
            break
        else
            aug([k m],:) = aug([m k],:)
            if aug(n,n) == 0
                fprintf('No unique solution exists.')
                break
            else
                for j = k+1:n
                    M(j,k) = aug(j,k)/aug(k,k)
                    for p = k:n+1
                        aug(j,p) = aug(j,p)-(M(j,k)*aug(k,p))
                    end
                end
            end
        end
    end
end

x(n) = (A(n,n+1))/(A(n,n))
for i = n-1:1
    x(i) = (1/A(i,i))(A(i,n+1) - symsum((A(i,j)*x(j)), j, [i+1, n]))
end
x(j) = x
end

A = [3.4, -6.12, -2.72; -0.5, 1.80, 0.80; 2, -4.86, 2.16;]
b = [0;2;1]
x = GaussElim(A,b)

[madhan ravi]

(1/A(i,i))
       %  ^-—- operator missing !

[Jordan Chancellor]

Thank you!! I fixed it.