<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def diffpow(self, x, rot=0):
 """Diffpow test objective function"""

        N = len(x)
        if rot:
            x = rotate(x)
        return sum(np.abs(x)**(2. + 4.*np.arange(N) / (N - 1.)))**0.5