content: """Test truncated SVD transformer."""
  
  import numpy as np
  import scipy.sparse as sp
  
  from sklearn.decomposition import TruncatedSVD
  from sklearn.utils import check_random_state
  from sklearn.utils.testing import (assert_array_almost_equal, assert_equal,
                                     assert_raises, assert_greater,
                                     assert_array_less)
  
  
  # Make an X that looks somewhat like a small tf-idf matrix.
  # XXX newer versions of SciPy have scipy.sparse.rand for this.
  shape = 60, 55
  n_samples, n_features = shape
  rng = check_random_state(42)
  X = rng.randint(-100, 20, np.product(shape)).reshape(shape)
  X = sp.csr_matrix(np.maximum(X, 0), dtype=np.float64)
  X.data[:] = 1 + np.log(X.data)
  Xdense = X.A
  
  
  def test_algorithms():
      svd_a = TruncatedSVD(30, algorithm="arpack")
      svd_r = TruncatedSVD(30, algorithm="randomized", random_state=42)
  
      Xa = svd_a.fit_transform(X)[:, :6]
      Xr = svd_r.fit_transform(X)[:, :6]
      assert_array_almost_equal(Xa, Xr, decimal=5)
  
      comp_a = np.abs(svd_a.components_)
      comp_r = np.abs(svd_r.components_)
      # All elements are equal, but some elements are more equal than others.
      assert_array_almost_equal(comp_a[:9], comp_r[:9])
      assert_array_almost_equal(comp_a[9:], comp_r[9:], decimal=2)
  
  
  def test_attributes():
      for n_components in (10, 25, 41):
          tsvd = TruncatedSVD(n_components).fit(X)
          assert_equal(tsvd.n_components, n_components)
          assert_equal(tsvd.components_.shape, (n_components, n_features))
  
  
  def test_too_many_components():
      for algorithm in ["arpack", "randomized"]:
          for n_components in (n_features, n_features + 1):
              tsvd = TruncatedSVD(n_components=n_components, algorithm=algorithm)
              assert_raises(ValueError, tsvd.fit, X)
  
  
  def test_sparse_formats():
      for fmt in ("array", "csr", "csc", "coo", "lil"):
          Xfmt = Xdense if fmt == "dense" else getattr(X, "to" + fmt)()
          tsvd = TruncatedSVD(n_components=11)
          Xtrans = tsvd.fit_transform(Xfmt)
          assert_equal(Xtrans.shape, (n_samples, 11))
          Xtrans = tsvd.transform(Xfmt)
          assert_equal(Xtrans.shape, (n_samples, 11))
  
  
  def test_inverse_transform():
      for algo in ("arpack", "randomized"):
          # We need a lot of components for the reconstruction to be "almost
          # equal" in all positions. XXX Test means or sums instead?
          tsvd = TruncatedSVD(n_components=52, random_state=42)
          Xt = tsvd.fit_transform(X)
          Xinv = tsvd.inverse_transform(Xt)
          assert_array_almost_equal(Xinv, Xdense, decimal=1)
  
  
  def test_integers():
      Xint = X.astype(np.int64)
      tsvd = TruncatedSVD(n_components=6)
      Xtrans = tsvd.fit_transform(Xint)
      assert_equal(Xtrans.shape, (n_samples, tsvd.n_components))
  
  
  def test_explained_variance():
      # Test sparse data
      svd_a_10_sp = TruncatedSVD(10, algorithm="arpack")
      svd_r_10_sp = TruncatedSVD(10, algorithm="randomized", random_state=42)
      svd_a_20_sp = TruncatedSVD(20, algorithm="arpack")
      svd_r_20_sp = TruncatedSVD(20, algorithm="randomized", random_state=42)
      X_trans_a_10_sp = svd_a_10_sp.fit_transform(X)
      X_trans_r_10_sp = svd_r_10_sp.fit_transform(X)
      X_trans_a_20_sp = svd_a_20_sp.fit_transform(X)
      X_trans_r_20_sp = svd_r_20_sp.fit_transform(X)
  
      # Test dense data
      svd_a_10_de = TruncatedSVD(10, algorithm="arpack")
      svd_r_10_de = TruncatedSVD(10, algorithm="randomized", random_state=42)
      svd_a_20_de = TruncatedSVD(20, algorithm="arpack")
      svd_r_20_de = TruncatedSVD(20, algorithm="randomized", random_state=42)
      X_trans_a_10_de = svd_a_10_de.fit_transform(X.toarray())
      X_trans_r_10_de = svd_r_10_de.fit_transform(X.toarray())
      X_trans_a_20_de = svd_a_20_de.fit_transform(X.toarray())
      X_trans_r_20_de = svd_r_20_de.fit_transform(X.toarray())
  
      # helper arrays for tests below
      svds = (svd_a_10_sp, svd_r_10_sp, svd_a_20_sp, svd_r_20_sp, svd_a_10_de,
              svd_r_10_de, svd_a_20_de, svd_r_20_de)
      svds_trans = (
          (svd_a_10_sp, X_trans_a_10_sp),
          (svd_r_10_sp, X_trans_r_10_sp),
          (svd_a_20_sp, X_trans_a_20_sp),
          (svd_r_20_sp, X_trans_r_20_sp),
          (svd_a_10_de, X_trans_a_10_de),
          (svd_r_10_de, X_trans_r_10_de),
          (svd_a_20_de, X_trans_a_20_de),
          (svd_r_20_de, X_trans_r_20_de),
      )
      svds_10_v_20 = (
          (svd_a_10_sp, svd_a_20_sp),
          (svd_r_10_sp, svd_r_20_sp),
          (svd_a_10_de, svd_a_20_de),
          (svd_r_10_de, svd_r_20_de),
      )
      svds_sparse_v_dense = (
          (svd_a_10_sp, svd_a_10_de),
          (svd_a_20_sp, svd_a_20_de),
          (svd_r_10_sp, svd_r_10_de),
          (svd_r_20_sp, svd_r_20_de),
      )
  
      # Assert the 1st component is equal
      for svd_10, svd_20 in svds_10_v_20:
          assert_array_almost_equal(
              svd_10.explained_variance_ratio_,
              svd_20.explained_variance_ratio_[:10],
              decimal=5,
          )
  
      # Assert that 20 components has higher explained variance than 10
      for svd_10, svd_20 in svds_10_v_20:
          assert_greater(
              svd_20.explained_variance_ratio_.sum(),
              svd_10.explained_variance_ratio_.sum(),
          )
  
      # Assert that all the values are greater than 0
      for svd in svds:
          assert_array_less(0.0, svd.explained_variance_ratio_)
  
      # Assert that total explained variance is less than 1
      for svd in svds:
          assert_array_less(svd.explained_variance_ratio_.sum(), 1.0)
  
      # Compare sparse vs. dense
      for svd_sparse, svd_dense in svds_sparse_v_dense:
          assert_array_almost_equal(svd_sparse.explained_variance_ratio_,
                                    svd_dense.explained_variance_ratio_)
  
      # Test that explained_variance is correct
      for svd, transformed in svds_trans:
          total_variance = np.var(X.toarray(), axis=0).sum()
          variances = np.var(transformed, axis=0)
          true_explained_variance_ratio = variances / total_variance
  
          assert_array_almost_equal(
              svd.explained_variance_ratio_,
              true_explained_variance_ratio,
          )
  