Merge pull request #540 from duncanhobbs/lgtm-warning-arma

Fix lgtm warning for arma.py.

Author: jstac

quantecon/arma.py

@@ -5,7 +5,6 @@
 
 """
 import numpy as np
-from numpy import conj
 from .util import check_random_state
 
 
@@ -206,7 +205,7 @@ def spectral_density(self, two_pi=True, res=1200):
         """
         from scipy.signal import freqz
         w, h = freqz(self.ma_poly, self.ar_poly, worN=res, whole=two_pi)
-        spect = h * conj(h) * self.sigma**2
+        spect = h * np.conj(h) * self.sigma**2
 
         return w, spect