Use entries of symbolic array outside of the array

I have defined a matrix of symbolic variables via

X=sym(x,[8,24]);

When I now type x5_24 for instance, MATLAB still says "Unrecognized function or variable x5_24". Why? I need to use the variable entries outside of the matrix X.

Answer 1

[Star Strider]

The reason is that the elements of ‘X’ are stored as matrix elements. The individual elements exist only as matrix elements, not as individual, named variables:

syms x 
X=sym('x',[8,24]);
Q = X(5,24)

produces:

Q =
x5_24

[Tobias Ohrmann]

ah okay, thx! and is there another way to create symbolic variables xi_j for iteratively?

[Ameer Hamza]

Read here why it is a bad idea: https://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer. Is there a reason that you cannot use matrix indexing to access an element?

[Tobias Ohrmann]

Its a bit complicated, I transported the matrix X to Mathematica, did something with it there and got a new matrix with variables xi_j, which I now want to transport back to MATLAB. So appareantly this was a bad idea..