^ operator

Hi,
I want to apply ^ operator to a vector but it is applied to some of the elements correctly and to some others, it generates NaN. Why is it not able to calculate -6.108576e-05^(1/3) even though it exists?


 tmp
[1] -6.108576e-05  4.208762e-05  3.547092e-05  7.171101e-04 -1.600269e-03

tmp^(1/3)

[1]        NaN 0.03478442 0.03285672 0.08950802        NaN

-6.108576e-05^(1/3)

[1] -0.03938341