If you define symbol variables in the book like this, you will report an error;

Symbolic variable names must be simple variable names;

Naming rules for variable names:

(1) The first character of the variable name must be an English letter.

(2) Variable names must not contain spaces, punctuation and operators, but they can be underlined.

For example, var_ 1_2 is legal.

(3) Do not have the same name as matlab keywords;

Your problem is that the variable name contains a percent sign.

You can try:

A = sym('A '，)