Use NuXMV to calculate exponentiation

Question

I want to use operator exp in NuXMV to calculate exponentiation. But the result is always 0.

I have written a simple program. The following is my program.

MODULE main
VAR
    exponentiation : real;
    res : real;
ASSIGN
    init(exponentiation) := 2.0;
    next(exponentiation) := exponentiation;
    init(res) := exp(exponentiation);
    next(res) := res;

The following is the running result.