Rick,
For OP's function in IML forum(You know where to find it) , You can't do that . because there is a kink in function. You can never find a interval [a,b], which f(a) and f(b) have different sign. They are all negative. Only x=0.99997 ,f(x) near 0 .
and more , if funciton is not differentiate or countious , you also can't do it .

In other words, My GA code is a good choice. The only thing you need to care about is defining a wide interval and make Object function value approximate zero.