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  import numpy as np
  
  from nose import SkipTest
  from distributions.tests.util import assert_close
  
  def _test_normals(nich, niw):
      mu = np.array([30.0])
      kappa = 0.3
      psi = np.array([[2.]])
      nu = 3
  
      # make the NIW case
      niw_shared = niw.Shared()
      niw_shared.load({'mu':mu,'kappa':kappa,'psi':psi,'nu':nu})
      niw_group = niw.Group()
      niw_group.init(niw_shared)
  
      # make the NIX case
      nix_shared = nich.Shared()
      nix_shared.load({'mu':mu[0],'kappa':kappa,'sigmasq':psi[0,0]/nu,'nu':nu})
      nix_group = nich.Group()
      nix_group.init(nix_shared)
  
      data = np.array([4., 54., 3., -12., 7., 10.])
      for d in data:
          niw_group.add_value(niw_shared, np.array([d]))
          nix_group.add_value(nix_shared, d)
  
      # check marginals
      assert_close(niw_group.score_data(niw_shared),
                   nix_group.score_data(nix_shared))
  
      # remove and check
      niw_group.remove_value(niw_shared, np.array([data[1]]))
      nix_group.remove_value(nix_shared, np.array([data[1]]))
  
      assert_close(niw_group.score_data(niw_shared),
                   nix_group.score_data(nix_shared))
  
      niw_group.remove_value(niw_shared, np.array([data[3]]))
      nix_group.remove_value(nix_shared, np.array([data[3]]))
  
      assert_close(niw_group.score_data(niw_shared),
                   nix_group.score_data(nix_shared))
  
      # check posterior predictive
      values = np.array([32., -0.1])
  
      for value in values:
          assert_close(niw_group.score_value(niw_shared, np.array([value])),
                       nix_group.score_value(nix_shared, value))
  
  def test_normals_dbg():
      try:
          from distributions.dbg.models import nich, niw
      except ImportError:
          raise SkipTest("no dbg.{nich,niw}")
      _test_normals(nich, niw)
  
  def test_normals_lp():
      try:
          from distributions.lp.models import nich, niw
      except ImportError:
          raise SkipTest("no dbg.{nich,niw}")
      _test_normals(nich, niw)
  
subject: add NIW/NIX comparison test