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from nifty import *
s=RGSpace(3,zerocenter=True)
f=Field(s,val=[0.,1.,2.])
op=FFTOperator(s)
print "op domain:", op.domain[0]
print "op target:", op.target[0]
print "op times real field", op.times(f).val

This prints

op domain: RGSpace(shape=(3,), zerocenter=(True,), distances=(0.33333333333333331,), harmonic=False)
op target: RGSpace(shape=(3,), zerocenter=(True,), distances=(1.0,), harmonic=True)
op times real field [-0.33333333+0.j        -0.16666667+0.8660254j  0.16666667+0.8660254j]

What I don't understand: if the target domain of the operator is zero-centered, why is the first value of the result real-only, and not the middle one?