Why y is a complx number? y = x.^(2/3)

x = -10:1:10
y = x.^(2/3)

Actually I try to plot y = x^(2/3)but I get warning from Matlab.
I try fplot(x^(2/3)[-10,10])

Answer 1

[Azzi Abdelmalek]

use 

y=abs(x.^(2/3))

You are calculating the roots of negative numbers, they are obviously complex

(-10)^(2/3) is ((-10)^(1/3))^2

Answer 2

[Walter Roberson]

Remember, in MATLAB, (2/3) is 0.333333<etc>, a floating point number, rather than being the indicator of taking the square of the third root of the number.

In MATLAB, when you raise a value to a non-integer power, the result x^y is defined as exp( log(x) * y). When x is negative, log(x) is complex. Multiplying a complex number by a floating point number is going to give you a complex number. exp() of a complex number is usually a complex number.