create_power_operator now processes the sqrt of a p**2 powerspectrum.

nifty/sugar.py

@@ -36,9 +36,10 @@ def create_power_operator(domain, power_spectrum, dtype=None,
     fp = Field(power_domain,
                val=power_spectrum, dtype=dtype,
                distribution_strategy=distribution_strategy)
+    fp **= 2
 
     f = fp.power_synthesize(mean=1, std=0, real_signal=False)
 
     power_operator = DiagonalOperator(domain, diagonal=f, bare=True)
 
-    return power_operator
\ No newline at end of file
+    return power_operator