Sya is defined in the code body, but not in the function. Read up on the scope of a Matlab variable for more information.
To fix this, you need to somehow define Sya within the functions in which you want to use it. This could be explicitly, by adding the line
Sya = 25;
to the function, or implicitly, by making it an argument of the function. Another option is to make Sya a global variable, but I don't know enough to advise on that and it's easy to use bad practices when using global variables so I'd suggest one of the other options.
global is slower. The location of the global variable must be searched at execution time when the "global" is encountered. The location of passed parameters is already known.
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