问题
Using MATLAB exponential function:
(-8)^0.333333
ans = 1.0000 + 1.7320i
How to get (-8)^0.333333 = -2 instead?
x=-10:-1;
x.^0.333333
How to get real value?
How to redefine ^:
x.^y
to
sign(x).*abs(x.^y))
回答1:
MATLAB 7.0 provides the NTHROOT function, which returns the real roots of a number. So your formula becomes NTHROOT(-8, 3) = -2
If you are using a version prior to MATLAB 7.0 (R14), please read the following:
To obtain the real cube root of a negative real number "x", rather than executing:
x.^(1/3)
use the command:
sign(x).*abs(x.^(1/3))
This will find the absolute value of the root and modify it by the sign of the argument.
See this
回答2:
There are 3 possible answers for the cube root of -8: -2, 1+/- sqrt(3)
You probably want nthroot(-8,3) --> -2
来源：https://stackoverflow.com/questions/7577595/how-to-get-80-333333-2-in-matlab