This is an expected behavior. Symbolic variables are created as complex by default.
In your case the equation is solved like this:
|z| == 1 => z = exp(j * y), y = [0, 2pi[
Meaning an infinite number of solutions along the unit circle. Only one solution is returned by default.
To get all the solutions you need to specify "ReturnConditions" as true:
>> solve(abs(x) == 1,'ReturnConditions',真正的)
In case you only want real solutions, you can get the expected result by making an assumption when declaring your variable:
>> syms xreal
>> solve(abs(x) == 1)% ans = [-1; 1]
>> solve(sqrt(x^2) == 1)% ans = [-1; 1]
您可以在以下文档页面上找到有关声明符号变量的更多信息：
