Indexing inside symbolic product

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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.

Risposta accettata

Walter Roberson
Walter Roberson il 25 Lug 2017
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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