As long as x.der and v.der are valid variables containing a scalar values or array, the '>' operator should work. With your code, it's hard to tell what all these variables are. This happens possibly because you are assigning a struct to x.der in this line:
x.der == v; % v is a stuct from previous line
And then, within your if-else, you are comparing a struct ('x') with a scalar value ('Xmax').
Instead of using if-else statement, a better approach is to use "assert" to test that all your variables are valid. Refer to the documentation here:
