Problems with creating a dynamic struct with num2str

for i = 1:9
    M.[num2str(i)] = zeros(3,3);
end

This gives me error, I have never really understood the syntaxis of num2str or how to use it with combination of text. This has probably a really simple answer but I havent been able to find it. Thanks for your time.

Answer 1

[Ive J]

First of all you cannot choose a digit as filed name due to the same reason you cannot choose it as a variable name.

for i = 1:9
    M.(['x', num2str(i)]) = zeros(3,3);
end

Or if you prefer strings:

for i = 1:9
    M.("x" + i) = zeros(3,3);
end