MATLAB: Indexing inside symbolic product

indexingsymbolicSymbolic Math Toolbox

I am trying to compute a symbolic product with the following code:
syms z theta_1 theta_2 k real
n = 2;
x = sym('x', [n 1])
assumeAlso(theta_2>0)
f = symfun(exp(-(z-theta_1)^2/(2*theta_2))/sqrt(2*pi*theta_2),[z, theta_1, theta_2])
L = symprod(f(x(k),theta_1,theta_2),k,1,n)
However, when I run the code I get the following error:
Error using sym/subsindex (line 766)
Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic variables and the body of the function is a SYM expression. When indexing, the input must be numeric, logical, or ':'.
Error in sym/subsref (line 805)
            R_tilde = builtin('subsref',L_tilde,Idx);
Could someone please explain what is going wrong here? Been staring at this for way to long.

Best Answer

Syms can never be used as indices.
Construct a vector of the individual values (sometimes this is very easy if only happen to use vectorizable operations), and then prod() the vector
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