code: from types import GeneratorType
  
  import numpy as np
  from numpy import linalg
  
  from scipy.sparse import dok_matrix, csr_matrix, issparse
  from scipy.spatial.distance import cosine, cityblock, minkowski, wminkowski
  from scipy.spatial.distance import cdist, pdist, squareform
  
  import pytest
  
  from sklearn import config_context
  
  from sklearn.utils._testing import assert_array_almost_equal
  from sklearn.utils._testing import assert_allclose
  from sklearn.utils._testing import assert_almost_equal
  from sklearn.utils._testing import assert_array_equal
  from sklearn.utils._testing import ignore_warnings
  
  from sklearn.metrics.pairwise import euclidean_distances
  from sklearn.metrics.pairwise import nan_euclidean_distances
  from sklearn.metrics.pairwise import manhattan_distances
  from sklearn.metrics.pairwise import haversine_distances
  from sklearn.metrics.pairwise import linear_kernel
  from sklearn.metrics.pairwise import chi2_kernel, additive_chi2_kernel
  from sklearn.metrics.pairwise import polynomial_kernel
  from sklearn.metrics.pairwise import rbf_kernel
  from sklearn.metrics.pairwise import laplacian_kernel
  from sklearn.metrics.pairwise import sigmoid_kernel
  from sklearn.metrics.pairwise import cosine_similarity
  from sklearn.metrics.pairwise import cosine_distances
  from sklearn.metrics.pairwise import pairwise_distances
  from sklearn.metrics.pairwise import pairwise_distances_chunked
  from sklearn.metrics.pairwise import pairwise_distances_argmin_min
  from sklearn.metrics.pairwise import pairwise_distances_argmin
  from sklearn.metrics.pairwise import pairwise_kernels
  from sklearn.metrics.pairwise import PAIRWISE_KERNEL_FUNCTIONS
  from sklearn.metrics.pairwise import PAIRWISE_DISTANCE_FUNCTIONS
  from sklearn.metrics.pairwise import PAIRWISE_BOOLEAN_FUNCTIONS
  from sklearn.metrics.pairwise import PAIRED_DISTANCES
  from sklearn.metrics.pairwise import check_pairwise_arrays
  from sklearn.metrics.pairwise import check_paired_arrays
  from sklearn.metrics.pairwise import paired_distances
  from sklearn.metrics.pairwise import paired_euclidean_distances
  from sklearn.metrics.pairwise import paired_manhattan_distances
  from sklearn.metrics.pairwise import _euclidean_distances_upcast
  from sklearn.preprocessing import normalize
  from sklearn.exceptions import DataConversionWarning
  
  
  def test_pairwise_distances():
      # Test the pairwise_distance helper function.
      rng = np.random.RandomState(0)
  
      # Euclidean distance should be equivalent to calling the function.
      X = rng.random_sample((5, 4))
      S = pairwise_distances(X, metric="euclidean")
      S2 = euclidean_distances(X)
      assert_array_almost_equal(S, S2)
  
      # Euclidean distance, with Y != X.
      Y = rng.random_sample((2, 4))
      S = pairwise_distances(X, Y, metric="euclidean")
      S2 = euclidean_distances(X, Y)
      assert_array_almost_equal(S, S2)
      # Check to ensure NaNs work with pairwise_distances.
      X_masked = rng.random_sample((5, 4))
      Y_masked = rng.random_sample((2, 4))
      X_masked[0, 0] = np.nan
      Y_masked[0, 0] = np.nan
      S_masked = pairwise_distances(X_masked, Y_masked, metric="nan_euclidean")
      S2_masked = nan_euclidean_distances(X_masked, Y_masked)
      assert_array_almost_equal(S_masked, S2_masked)
      # Test with tuples as X and Y
      X_tuples = tuple([tuple([v for v in row]) for row in X])
      Y_tuples = tuple([tuple([v for v in row]) for row in Y])
      S2 = pairwise_distances(X_tuples, Y_tuples, metric="euclidean")
      assert_array_almost_equal(S, S2)
  
      # Test haversine distance
      # The data should be valid latitude and longitude
      X = rng.random_sample((5, 2))
      X[:, 0] = (X[:, 0] - 0.5) * 2 * np.pi/2
      X[:, 1] = (X[:, 1] - 0.5) * 2 * np.pi
      S = pairwise_distances(X, metric="haversine")
      S2 = haversine_distances(X)
      assert_array_almost_equal(S, S2)
  
      # Test haversine distance, with Y != X
      Y = rng.random_sample((2, 2))
      Y[:, 0] = (Y[:, 0] - 0.5)*2*np.pi/2
      Y[:, 1] = (Y[:, 1] - 0.5)*2*np.pi
      S = pairwise_distances(X, Y, metric="haversine")
      S2 = haversine_distances(X, Y)
      assert_array_almost_equal(S, S2)
  
      # "cityblock" uses scikit-learn metric, cityblock (function) is
      # scipy.spatial.
      S = pairwise_distances(X, metric="cityblock")
      S2 = pairwise_distances(X, metric=cityblock)
      assert S.shape[0] == S.shape[1]
      assert S.shape[0] == X.shape[0]
      assert_array_almost_equal(S, S2)
  
      # The manhattan metric should be equivalent to cityblock.
      S = pairwise_distances(X, Y, metric="manhattan")
      S2 = pairwise_distances(X, Y, metric=cityblock)
      assert S.shape[0] == X.shape[0]
      assert S.shape[1] == Y.shape[0]
      assert_array_almost_equal(S, S2)
  
      # Test cosine as a string metric versus cosine callable
      # The string "cosine" uses sklearn.metric,
      # while the function cosine is scipy.spatial
      S = pairwise_distances(X, Y, metric="cosine")
      S2 = pairwise_distances(X, Y, metric=cosine)
      assert S.shape[0] == X.shape[0]
      assert S.shape[1] == Y.shape[0]
      assert_array_almost_equal(S, S2)
  
      # Test with sparse X and Y,
      # currently only supported for Euclidean, L1 and cosine.
      X_sparse = csr_matrix(X)
      Y_sparse = csr_matrix(Y)
      S = pairwise_distances(X_sparse, Y_sparse, metric="euclidean")
      S2 = euclidean_distances(X_sparse, Y_sparse)
      assert_array_almost_equal(S, S2)
      S = pairwise_distances(X_sparse, Y_sparse, metric="cosine")
      S2 = cosine_distances(X_sparse, Y_sparse)
      assert_array_almost_equal(S, S2)
      S = pairwise_distances(X_sparse, Y_sparse.tocsc(), metric="manhattan")
      S2 = manhattan_distances(X_sparse.tobsr(), Y_sparse.tocoo())
      assert_array_almost_equal(S, S2)
      S2 = manhattan_distances(X, Y)
      assert_array_almost_equal(S, S2)
  
      # Test with scipy.spatial.distance metric, with a kwd
      kwds = {"p": 2.0}
      S = pairwise_distances(X, Y, metric="minkowski", **kwds)
      S2 = pairwise_distances(X, Y, metric=minkowski, **kwds)
      assert_array_almost_equal(S, S2)
  
      # same with Y = None
      kwds = {"p": 2.0}
      S = pairwise_distances(X, metric="minkowski", **kwds)
      S2 = pairwise_distances(X, metric=minkowski, **kwds)
      assert_array_almost_equal(S, S2)
  
      # Test that scipy distance metrics throw an error if sparse matrix given
      with pytest.raises(TypeError):
          pairwise_distances(X_sparse, metric="minkowski")
      with pytest.raises(TypeError):
          pairwise_distances(X, Y_sparse, metric="minkowski")
  
      # Test that a value error is raised if the metric is unknown
      with pytest.raises(ValueError):
          pairwise_distances(X, Y, metric="blah")
  
  
  @pytest.mark.parametrize('metric', PAIRWISE_BOOLEAN_FUNCTIONS)
  def test_pairwise_boolean_distance(metric):
      # test that we convert to boolean arrays for boolean distances
      rng = np.random.RandomState(0)
      X = rng.randn(5, 4)
      Y = X.copy()
      Y[0, 0] = 1 - Y[0, 0]
  
      # ignore conversion to boolean in pairwise_distances
      with ignore_warnings(category=DataConversionWarning):
          for Z in [Y, None]:
              res = pairwise_distances(X, Z, metric=metric)
              res[np.isnan(res)] = 0
              assert np.sum(res != 0) == 0
  
      # non-boolean arrays are converted to boolean for boolean
      # distance metrics with a data conversion warning
      msg = "Data was converted to boolean for metric %s" % metric
      with pytest.warns(DataConversionWarning, match=msg):
          pairwise_distances(X, metric=metric)
  
      # Check that the warning is raised if X is boolean by Y is not boolean:
      with pytest.warns(DataConversionWarning, match=msg):
          pairwise_distances(X.astype(bool), Y=Y, metric=metric)
  
      # Check that no warning is raised if X is already boolean and Y is None:
      with pytest.warns(None) as records:
          pairwise_distances(X.astype(bool), metric=metric)
      assert len(records) == 0
  
  
  def test_no_data_conversion_warning():
      # No warnings issued if metric is not a boolean distance function
      rng = np.random.RandomState(0)
      X = rng.randn(5, 4)
      with pytest.warns(None) as records:
          pairwise_distances(X, metric="minkowski")
      assert len(records) == 0
  
  
  @pytest.mark.parametrize('func', [pairwise_distances, pairwise_kernels])
  def test_pairwise_precomputed(func):
      # Test correct shape
      with pytest.raises(ValueError, match='.* shape .*'):
          func(np.zeros((5, 3)), metric='precomputed')
      # with two args
      with pytest.raises(ValueError, match='.* shape .*'):
          func(np.zeros((5, 3)), np.zeros((4, 4)), metric='precomputed')
      # even if shape[1] agrees (although thus second arg is spurious)
      with pytest.raises(ValueError, match='.* shape .*'):
          func(np.zeros((5, 3)), np.zeros((4, 3)), metric='precomputed')
  
      # Test not copied (if appropriate dtype)
      S = np.zeros((5, 5))
      S2 = func(S, metric="precomputed")
      assert S is S2
      # with two args
      S = np.zeros((5, 3))
      S2 = func(S, np.zeros((3, 3)), metric="precomputed")
      assert S is S2
  
      # Test always returns float dtype
      S = func(np.array([[1]], dtype='int'), metric='precomputed')
      assert 'f' == S.dtype.kind
  
      # Test converts list to array-like
      S = func([[1.]], metric='precomputed')
      assert isinstance(S, np.ndarray)
  
  
  def test_pairwise_precomputed_non_negative():
      # Test non-negative values
      with pytest.raises(ValueError, match='.* non-negative values.*'):
          pairwise_distances(np.full((5, 5), -1), metric='precomputed')
  
  
  _wminkowski_kwds = {'w': np.arange(1, 5).astype('double', copy=False), 'p': 1}
  
  
  def callable_rbf_kernel(x, y, **kwds):
      # Callable version of pairwise.rbf_kernel.
      K = rbf_kernel(np.atleast_2d(x), np.atleast_2d(y), **kwds)
      return K
  
  
  @pytest.mark.parametrize(
          'func, metric, kwds',
          [(pairwise_distances, 'euclidean', {}),
           (pairwise_distances, wminkowski, _wminkowski_kwds),
           (pairwise_distances, 'wminkowski', _wminkowski_kwds),
           (pairwise_kernels, 'polynomial', {'degree': 1}),
           (pairwise_kernels, callable_rbf_kernel, {'gamma': .1})])
  @pytest.mark.parametrize('array_constr', [np.array, csr_matrix])
  @pytest.mark.parametrize('dtype', [np.float64, int])
  def test_pairwise_parallel(func, metric, kwds, array_constr, dtype):
      rng = np.random.RandomState(0)
      X = array_constr(5 * rng.random_sample((5, 4)), dtype=dtype)
      Y = array_constr(5 * rng.random_sample((3, 4)), dtype=dtype)
  
      try:
          S = func(X, metric=metric, n_jobs=1, **kwds)
      except (TypeError, ValueError) as exc:
          # Not all metrics support sparse input
          # ValueError may be triggered by bad callable
          if array_constr is csr_matrix:
              with pytest.raises(type(exc)):
                  func(X, metric=metric, n_jobs=2, **kwds)
              return
          else:
              raise
      S2 = func(X, metric=metric, n_jobs=2, **kwds)
      assert_allclose(S, S2)
  
      S = func(X, Y, metric=metric, n_jobs=1, **kwds)
      S2 = func(X, Y, metric=metric, n_jobs=2, **kwds)
      assert_allclose(S, S2)
  
  
  def test_pairwise_callable_nonstrict_metric():
      # paired_distances should allow callable metric where metric(x, x) != 0
      # Knowing that the callable is a strict metric would allow the diagonal to
      # be left uncalculated and set to 0.
      assert pairwise_distances([[1.]], metric=lambda x, y: 5)[0, 0] == 5
  
  
  # Test with all metrics that should be in PAIRWISE_KERNEL_FUNCTIONS.
  @pytest.mark.parametrize(
          'metric',
          ["rbf", "laplacian", "sigmoid", "polynomial", "linear",
           "chi2", "additive_chi2"])
  def test_pairwise_kernels(metric):
      # Test the pairwise_kernels helper function.
  
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((2, 4))
      function = PAIRWISE_KERNEL_FUNCTIONS[metric]
      # Test with Y=None
      K1 = pairwise_kernels(X, metric=metric)
      K2 = function(X)
      assert_array_almost_equal(K1, K2)
      # Test with Y=Y
      K1 = pairwise_kernels(X, Y=Y, metric=metric)
      K2 = function(X, Y=Y)
      assert_array_almost_equal(K1, K2)
      # Test with tuples as X and Y
      X_tuples = tuple([tuple([v for v in row]) for row in X])
      Y_tuples = tuple([tuple([v for v in row]) for row in Y])
      K2 = pairwise_kernels(X_tuples, Y_tuples, metric=metric)
      assert_array_almost_equal(K1, K2)
  
      # Test with sparse X and Y
      X_sparse = csr_matrix(X)
      Y_sparse = csr_matrix(Y)
      if metric in ["chi2", "additive_chi2"]:
          # these don't support sparse matrices yet
          with pytest.raises(ValueError):
              pairwise_kernels(X_sparse, Y=Y_sparse,
                               metric=metric)
          return
      K1 = pairwise_kernels(X_sparse, Y=Y_sparse, metric=metric)
      assert_array_almost_equal(K1, K2)
  
  
  def test_pairwise_kernels_callable():
      # Test the pairwise_kernels helper function
      # with a callable function, with given keywords.
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((2, 4))
  
      metric = callable_rbf_kernel
      kwds = {'gamma': 0.1}
      K1 = pairwise_kernels(X, Y=Y, metric=metric, **kwds)
      K2 = rbf_kernel(X, Y=Y, **kwds)
      assert_array_almost_equal(K1, K2)
  
      # callable function, X=Y
      K1 = pairwise_kernels(X, Y=X, metric=metric, **kwds)
      K2 = rbf_kernel(X, Y=X, **kwds)
      assert_array_almost_equal(K1, K2)
  
  
  def test_pairwise_kernels_filter_param():
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((2, 4))
      K = rbf_kernel(X, Y, gamma=0.1)
      params = {"gamma": 0.1, "blabla": ":)"}
      K2 = pairwise_kernels(X, Y, metric="rbf", filter_params=True, **params)
      assert_array_almost_equal(K, K2)
  
      with pytest.raises(TypeError):
          pairwise_kernels(X, Y, "rbf", **params)
  
  
  @pytest.mark.parametrize('metric, func', PAIRED_DISTANCES.items())
  def test_paired_distances(metric, func):
      # Test the pairwise_distance helper function.
      rng = np.random.RandomState(0)
      # Euclidean distance should be equivalent to calling the function.
      X = rng.random_sample((5, 4))
      # Euclidean distance, with Y != X.
      Y = rng.random_sample((5, 4))
  
      S = paired_distances(X, Y, metric=metric)
      S2 = func(X, Y)
      assert_array_almost_equal(S, S2)
      S3 = func(csr_matrix(X), csr_matrix(Y))
      assert_array_almost_equal(S, S3)
      if metric in PAIRWISE_DISTANCE_FUNCTIONS:
          # Check the pairwise_distances implementation
          # gives the same value
          distances = PAIRWISE_DISTANCE_FUNCTIONS[metric](X, Y)
          distances = np.diag(distances)
          assert_array_almost_equal(distances, S)
  
  
  def test_paired_distances_callable():
      # Test the pairwise_distance helper function
      # with the callable implementation
      rng = np.random.RandomState(0)
      # Euclidean distance should be equivalent to calling the function.
      X = rng.random_sample((5, 4))
      # Euclidean distance, with Y != X.
      Y = rng.random_sample((5, 4))
  
      S = paired_distances(X, Y, metric='manhattan')
      S2 = paired_distances(X, Y, metric=lambda x, y: np.abs(x - y).sum(axis=0))
      assert_array_almost_equal(S, S2)
  
      # Test that a value error is raised when the lengths of X and Y should not
      # differ
      Y = rng.random_sample((3, 4))
      with pytest.raises(ValueError):
          paired_distances(X, Y)
  
  
  def test_pairwise_distances_argmin_min():
      # Check pairwise minimum distances computation for any metric
      X = [[0], [1]]
      Y = [[-2], [3]]
  
      Xsp = dok_matrix(X)
      Ysp = csr_matrix(Y, dtype=np.float32)
  
      expected_idx = [0, 1]
      expected_vals = [2, 2]
      expected_vals_sq = [4, 4]
  
      # euclidean metric
      idx, vals = pairwise_distances_argmin_min(X, Y, metric="euclidean")
      idx2 = pairwise_distances_argmin(X, Y, metric="euclidean")
      assert_array_almost_equal(idx, expected_idx)
      assert_array_almost_equal(idx2, expected_idx)
      assert_array_almost_equal(vals, expected_vals)
      # sparse matrix case
      idxsp, valssp = pairwise_distances_argmin_min(Xsp, Ysp, metric="euclidean")
      assert_array_almost_equal(idxsp, expected_idx)
      assert_array_almost_equal(valssp, expected_vals)
      # We don't want np.matrix here
      assert type(idxsp) == np.ndarray
      assert type(valssp) == np.ndarray
  
      # euclidean metric squared
      idx, vals = pairwise_distances_argmin_min(X, Y, metric="euclidean",
                                                metric_kwargs={"squared": True})
      assert_array_almost_equal(idx, expected_idx)
      assert_array_almost_equal(vals, expected_vals_sq)
  
      # Non-euclidean scikit-learn metric
      idx, vals = pairwise_distances_argmin_min(X, Y, metric="manhattan")
      idx2 = pairwise_distances_argmin(X, Y, metric="manhattan")
      assert_array_almost_equal(idx, expected_idx)
      assert_array_almost_equal(idx2, expected_idx)
      assert_array_almost_equal(vals, expected_vals)
      # sparse matrix case
      idxsp, valssp = pairwise_distances_argmin_min(Xsp, Ysp, metric="manhattan")
      assert_array_almost_equal(idxsp, expected_idx)
      assert_array_almost_equal(valssp, expected_vals)
  
      # Non-euclidean Scipy distance (callable)
      idx, vals = pairwise_distances_argmin_min(X, Y, metric=minkowski,
                                                metric_kwargs={"p": 2})
      assert_array_almost_equal(idx, expected_idx)
      assert_array_almost_equal(vals, expected_vals)
  
      # Non-euclidean Scipy distance (string)
      idx, vals = pairwise_distances_argmin_min(X, Y, metric="minkowski",
                                                metric_kwargs={"p": 2})
      assert_array_almost_equal(idx, expected_idx)
      assert_array_almost_equal(vals, expected_vals)
  
      # Compare with naive implementation
      rng = np.random.RandomState(0)
      X = rng.randn(97, 149)
      Y = rng.randn(111, 149)
  
      dist = pairwise_distances(X, Y, metric="manhattan")
      dist_orig_ind = dist.argmin(axis=0)
      dist_orig_val = dist[dist_orig_ind, range(len(dist_orig_ind))]
  
      dist_chunked_ind, dist_chunked_val = pairwise_distances_argmin_min(
          X, Y, axis=0, metric="manhattan")
      np.testing.assert_almost_equal(dist_orig_ind, dist_chunked_ind, decimal=7)
      np.testing.assert_almost_equal(dist_orig_val, dist_chunked_val, decimal=7)
  
  
  def _reduce_func(dist, start):
      return dist[:, :100]
  
  
  def test_pairwise_distances_chunked_reduce():
      rng = np.random.RandomState(0)
      X = rng.random_sample((400, 4))
      # Reduced Euclidean distance
      S = pairwise_distances(X)[:, :100]
      S_chunks = pairwise_distances_chunked(X, None, reduce_func=_reduce_func,
                                            working_memory=2 ** -16)
      assert isinstance(S_chunks, GeneratorType)
      S_chunks = list(S_chunks)
      assert len(S_chunks) > 1
      # atol is for diagonal where S is explicitly zeroed on the diagonal
      assert_allclose(np.vstack(S_chunks), S, atol=1e-7)
  
  
  @pytest.mark.parametrize('good_reduce', [
      lambda D, start: list(D),
      lambda D, start: np.array(D),
      lambda D, start: csr_matrix(D),
      lambda D, start: (list(D), list(D)),
      lambda D, start: (dok_matrix(D), np.array(D), list(D)),
      ])
  def test_pairwise_distances_chunked_reduce_valid(good_reduce):
      X = np.arange(10).reshape(-1, 1)
      S_chunks = pairwise_distances_chunked(X, None, reduce_func=good_reduce,
                                            working_memory=64)
      next(S_chunks)
  
  
  @pytest.mark.parametrize(('bad_reduce', 'err_type', 'message'), [
      (lambda D, s: np.concatenate([D, D[-1:]]), ValueError,
       r'length 11\..* input: 10\.'),
      (lambda D, s: (D, np.concatenate([D, D[-1:]])), ValueError,
       r'length \(10, 11\)\..* input: 10\.'),
      (lambda D, s: (D[:9], D), ValueError,
       r'length \(9, 10\)\..* input: 10\.'),
      (lambda D, s: 7, TypeError,
       r'returned 7\. Expected sequence\(s\) of length 10\.'),
      (lambda D, s: (7, 8), TypeError,
       r'returned \(7, 8\)\. Expected sequence\(s\) of length 10\.'),
      (lambda D, s: (np.arange(10), 9), TypeError,
       r', 9\)\. Expected sequence\(s\) of length 10\.'),
  ])
  def test_pairwise_distances_chunked_reduce_invalid(bad_reduce, err_type,
                                                     message):
      X = np.arange(10).reshape(-1, 1)
      S_chunks = pairwise_distances_chunked(X, None, reduce_func=bad_reduce,
                                            working_memory=64)
      with pytest.raises(err_type, match=message):
          next(S_chunks)
  
  
  def check_pairwise_distances_chunked(X, Y, working_memory, metric='euclidean'):
      gen = pairwise_distances_chunked(X, Y, working_memory=working_memory,
                                       metric=metric)
      assert isinstance(gen, GeneratorType)
      blockwise_distances = list(gen)
      Y = X if Y is None else Y
      min_block_mib = len(Y) * 8 * 2 ** -20
  
      for block in blockwise_distances:
          memory_used = block.nbytes
          assert memory_used <= max(working_memory, min_block_mib) * 2 ** 20
  
      blockwise_distances = np.vstack(blockwise_distances)
      S = pairwise_distances(X, Y, metric=metric)
      assert_array_almost_equal(blockwise_distances, S)
  
  
  @pytest.mark.parametrize(
          'metric',
          ('euclidean', 'l2', 'sqeuclidean'))
  def test_pairwise_distances_chunked_diagonal(metric):
      rng = np.random.RandomState(0)
      X = rng.normal(size=(1000, 10), scale=1e10)
      chunks = list(pairwise_distances_chunked(X, working_memory=1,
                                               metric=metric))
      assert len(chunks) > 1
      assert_array_almost_equal(np.diag(np.vstack(chunks)), 0, decimal=10)
  
  
  @pytest.mark.parametrize(
          'metric',
          ('euclidean', 'l2', 'sqeuclidean'))
  def test_parallel_pairwise_distances_diagonal(metric):
      rng = np.random.RandomState(0)
      X = rng.normal(size=(1000, 10), scale=1e10)
      distances = pairwise_distances(X, metric=metric, n_jobs=2)
      assert_allclose(np.diag(distances), 0, atol=1e-10)
  
  
  @ignore_warnings
  def test_pairwise_distances_chunked():
      # Test the pairwise_distance helper function.
      rng = np.random.RandomState(0)
      # Euclidean distance should be equivalent to calling the function.
      X = rng.random_sample((200, 4))
      check_pairwise_distances_chunked(X, None, working_memory=1,
                                       metric='euclidean')
      # Test small amounts of memory
      for power in range(-16, 0):
          check_pairwise_distances_chunked(X, None, working_memory=2 ** power,
                                           metric='euclidean')
      # X as list
      check_pairwise_distances_chunked(X.tolist(), None, working_memory=1,
                                       metric='euclidean')
      # Euclidean distance, with Y != X.
      Y = rng.random_sample((100, 4))
      check_pairwise_distances_chunked(X, Y, working_memory=1,
                                       metric='euclidean')
      check_pairwise_distances_chunked(X.tolist(), Y.tolist(), working_memory=1,
                                       metric='euclidean')
      # absurdly large working_memory
      check_pairwise_distances_chunked(X, Y, working_memory=10000,
                                       metric='euclidean')
      # "cityblock" uses scikit-learn metric, cityblock (function) is
      # scipy.spatial.
      check_pairwise_distances_chunked(X, Y, working_memory=1,
                                       metric='cityblock')
      # Test that a value error is raised if the metric is unknown
      with pytest.raises(ValueError):
          next(pairwise_distances_chunked(X, Y, metric="blah"))
  
      # Test precomputed returns all at once
      D = pairwise_distances(X)
      gen = pairwise_distances_chunked(D,
                                       working_memory=2 ** -16,
                                       metric='precomputed')
      assert isinstance(gen, GeneratorType)
      assert next(gen) is D
      with pytest.raises(StopIteration):
          next(gen)
  
  
  @pytest.mark.parametrize("x_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  @pytest.mark.parametrize("y_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances_known_result(x_array_constr, y_array_constr):
      # Check the pairwise Euclidean distances computation on known result
      X = x_array_constr([[0]])
      Y = y_array_constr([[1], [2]])
      D = euclidean_distances(X, Y)
      assert_allclose(D, [[1., 2.]])
  
  
  @pytest.mark.parametrize("dtype", [np.float32, np.float64])
  @pytest.mark.parametrize("y_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances_with_norms(dtype, y_array_constr):
      # check that we still get the right answers with {X,Y}_norm_squared
      # and that we get a wrong answer with wrong {X,Y}_norm_squared
      rng = np.random.RandomState(0)
      X = rng.random_sample((10, 10)).astype(dtype, copy=False)
      Y = rng.random_sample((20, 10)).astype(dtype, copy=False)
  
      # norms will only be used if their dtype is float64
      X_norm_sq = (X.astype(np.float64) ** 2).sum(axis=1).reshape(1, -1)
      Y_norm_sq = (Y.astype(np.float64) ** 2).sum(axis=1).reshape(1, -1)
  
      Y = y_array_constr(Y)
  
      D1 = euclidean_distances(X, Y)
      D2 = euclidean_distances(X, Y, X_norm_squared=X_norm_sq)
      D3 = euclidean_distances(X, Y, Y_norm_squared=Y_norm_sq)
      D4 = euclidean_distances(X, Y, X_norm_squared=X_norm_sq,
                               Y_norm_squared=Y_norm_sq)
      assert_allclose(D2, D1)
      assert_allclose(D3, D1)
      assert_allclose(D4, D1)
  
      # check we get the wrong answer with wrong {X,Y}_norm_squared
      wrong_D = euclidean_distances(X, Y,
                                    X_norm_squared=np.zeros_like(X_norm_sq),
                                    Y_norm_squared=np.zeros_like(Y_norm_sq))
      with pytest.raises(AssertionError):
          assert_allclose(wrong_D, D1)
  
  
  @pytest.mark.parametrize("dtype", [np.float32, np.float64])
  @pytest.mark.parametrize("x_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  @pytest.mark.parametrize("y_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances(dtype, x_array_constr, y_array_constr):
      # check that euclidean distances gives same result as scipy cdist
      # when X and Y != X are provided
      rng = np.random.RandomState(0)
      X = rng.random_sample((100, 10)).astype(dtype, copy=False)
      X[X < 0.8] = 0
      Y = rng.random_sample((10, 10)).astype(dtype, copy=False)
      Y[Y < 0.8] = 0
  
      expected = cdist(X, Y)
  
      X = x_array_constr(X)
      Y = y_array_constr(Y)
      distances = euclidean_distances(X, Y)
  
      # the default rtol=1e-7 is too close to the float32 precision
      # and fails due too rounding errors.
      assert_allclose(distances, expected, rtol=1e-6)
      assert distances.dtype == dtype
  
  
  @pytest.mark.parametrize("dtype", [np.float32, np.float64])
  @pytest.mark.parametrize("x_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances_sym(dtype, x_array_constr):
      # check that euclidean distances gives same result as scipy pdist
      # when only X is provided
      rng = np.random.RandomState(0)
      X = rng.random_sample((100, 10)).astype(dtype, copy=False)
      X[X < 0.8] = 0
  
      expected = squareform(pdist(X))
  
      X = x_array_constr(X)
      distances = euclidean_distances(X)
  
      # the default rtol=1e-7 is too close to the float32 precision
      # and fails due too rounding errors.
      assert_allclose(distances, expected, rtol=1e-6)
      assert distances.dtype == dtype
  
  
  @pytest.mark.parametrize("batch_size", [None, 5, 7, 101])
  @pytest.mark.parametrize("x_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  @pytest.mark.parametrize("y_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances_upcast(batch_size, x_array_constr,
                                      y_array_constr):
      # check batches handling when Y != X (#13910)
      rng = np.random.RandomState(0)
      X = rng.random_sample((100, 10)).astype(np.float32)
      X[X < 0.8] = 0
      Y = rng.random_sample((10, 10)).astype(np.float32)
      Y[Y < 0.8] = 0
  
      expected = cdist(X, Y)
  
      X = x_array_constr(X)
      Y = y_array_constr(Y)
      distances = _euclidean_distances_upcast(X, Y=Y, batch_size=batch_size)
      distances = np.sqrt(np.maximum(distances, 0))
  
      # the default rtol=1e-7 is too close to the float32 precision
      # and fails due too rounding errors.
      assert_allclose(distances, expected, rtol=1e-6)
  
  
  @pytest.mark.parametrize("batch_size", [None, 5, 7, 101])
  @pytest.mark.parametrize("x_array_constr", [np.array, csr_matrix],
                           ids=["dense", "sparse"])
  def test_euclidean_distances_upcast_sym(batch_size, x_array_constr):
      # check batches handling when X is Y (#13910)
      rng = np.random.RandomState(0)
      X = rng.random_sample((100, 10)).astype(np.float32)
      X[X < 0.8] = 0
  
      expected = squareform(pdist(X))
  
      X = x_array_constr(X)
      distances = _euclidean_distances_upcast(X, Y=X, batch_size=batch_size)
      distances = np.sqrt(np.maximum(distances, 0))
  
      # the default rtol=1e-7 is too close to the float32 precision
      # and fails due too rounding errors.
      assert_allclose(distances, expected, rtol=1e-6)
  
  
  @pytest.mark.parametrize(
      "dtype, eps, rtol",
      [(np.float32, 1e-4, 1e-5),
       pytest.param(
           np.float64, 1e-8, 0.99,
           marks=pytest.mark.xfail(reason='failing due to lack of precision'))])
  @pytest.mark.parametrize("dim", [1, 1000000])
  def test_euclidean_distances_extreme_values(dtype, eps, rtol, dim):
      # check that euclidean distances is correct with float32 input thanks to
      # upcasting. On float64 there are still precision issues.
      X = np.array([[1.] * dim], dtype=dtype)
      Y = np.array([[1. + eps] * dim], dtype=dtype)
  
      distances = euclidean_distances(X, Y)
      expected = cdist(X, Y)
  
      assert_allclose(distances, expected, rtol=1e-5)
  
  
  @pytest.mark.parametrize("squared", [True, False])
  def test_nan_euclidean_distances_equal_to_euclidean_distance(squared):
      # with no nan values
      rng = np.random.RandomState(1337)
      X = rng.randn(3, 4)
      Y = rng.randn(4, 4)
  
      normal_distance = euclidean_distances(X, Y=Y, squared=squared)
      nan_distance = nan_euclidean_distances(X, Y=Y, squared=squared)
      assert_allclose(normal_distance, nan_distance)
  
  
  @pytest.mark.parametrize(
      "X", [np.array([[np.inf, 0]]), np.array([[0, -np.inf]])])
  @pytest.mark.parametrize(
      "Y", [np.array([[np.inf, 0]]), np.array([[0, -np.inf]]), None])
  def test_nan_euclidean_distances_infinite_values(X, Y):
  
      with pytest.raises(ValueError) as excinfo:
          nan_euclidean_distances(X, Y=Y)
  
      exp_msg = ("Input contains infinity or a value too large for "
                 "dtype('float64').")
      assert exp_msg == str(excinfo.value)
  
  
  @pytest.mark.parametrize("X, X_diag, missing_value", [
      (np.array([[0, 1], [1, 0]]), np.sqrt(2), np.nan),
      (np.array([[0, 1], [1, np.nan]]), np.sqrt(2), np.nan),
      (np.array([[np.nan, 1], [1, np.nan]]), np.nan, np.nan),
      (np.array([[np.nan, 1], [np.nan, 0]]), np.sqrt(2), np.nan),
      (np.array([[0, np.nan], [1, np.nan]]), np.sqrt(2), np.nan),
      (np.array([[0, 1], [1, 0]]), np.sqrt(2), -1),
      (np.array([[0, 1], [1, -1]]), np.sqrt(2), -1),
      (np.array([[-1, 1], [1, -1]]), np.nan, -1),
      (np.array([[-1, 1], [-1, 0]]), np.sqrt(2), -1),
      (np.array([[0, -1], [1, -1]]), np.sqrt(2), -1)
  ])
  def test_nan_euclidean_distances_2x2(X, X_diag, missing_value):
  
      exp_dist = np.array([[0., X_diag], [X_diag, 0]])
  
      dist = nan_euclidean_distances(X, missing_values=missing_value)
      assert_allclose(exp_dist, dist)
  
      dist_sq = nan_euclidean_distances(
          X, squared=True, missing_values=missing_value)
      assert_allclose(exp_dist**2, dist_sq)
  
      dist_two = nan_euclidean_distances(X, X, missing_values=missing_value)
      assert_allclose(exp_dist, dist_two)
  
      dist_two_copy = nan_euclidean_distances(
          X, X.copy(), missing_values=missing_value)
      assert_allclose(exp_dist, dist_two_copy)
  
  
  @pytest.mark.parametrize("missing_value", [np.nan, -1])
  def test_nan_euclidean_distances_complete_nan(missing_value):
      X = np.array([[missing_value, missing_value], [0, 1]])
  
      exp_dist = np.array([[np.nan, np.nan], [np.nan, 0]])
  
      dist = nan_euclidean_distances(X, missing_values=missing_value)
      assert_allclose(exp_dist, dist)
  
      dist = nan_euclidean_distances(
              X, X.copy(), missing_values=missing_value)
      assert_allclose(exp_dist, dist)
  
  
  @pytest.mark.parametrize("missing_value", [np.nan, -1])
  def test_nan_euclidean_distances_not_trival(missing_value):
      X = np.array([[1., missing_value, 3., 4., 2.],
                    [missing_value, 4., 6., 1., missing_value],
                    [3., missing_value, missing_value, missing_value, 1.]])
  
      Y = np.array([[missing_value, 7., 7., missing_value, 2.],
                    [missing_value, missing_value, 5., 4., 7.],
                    [missing_value, missing_value, missing_value, 4., 5.]])
  
      # Check for symmetry
      D1 = nan_euclidean_distances(X, Y,  missing_values=missing_value)
      D2 = nan_euclidean_distances(Y, X, missing_values=missing_value)
  
      assert_almost_equal(D1, D2.T)
  
      # Check with explicit formula and squared=True
      assert_allclose(
          nan_euclidean_distances(
              X[:1], Y[:1], squared=True, missing_values=missing_value),
          [[5.0 / 2.0 * ((7 - 3)**2 + (2 - 2)**2)]])
  
      # Check with explicit formula and squared=False
      assert_allclose(
          nan_euclidean_distances(
              X[1:2], Y[1:2], squared=False, missing_values=missing_value),
          [[np.sqrt(5.0 / 2.0 * ((6 - 5)**2 + (1 - 4)**2))]])
  
      # Check when Y = X is explicitly passed
      D3 = nan_euclidean_distances(X, missing_values=missing_value)
      D4 = nan_euclidean_distances(X, X, missing_values=missing_value)
      D5 = nan_euclidean_distances(X, X.copy(), missing_values=missing_value)
      assert_allclose(D3, D4)
      assert_allclose(D4, D5)
  
      # Check copy = True against copy = False
      D6 = nan_euclidean_distances(X, Y, copy=True)
      D7 = nan_euclidean_distances(X, Y, copy=False)
      assert_allclose(D6, D7)
  
  
  @pytest.mark.parametrize("missing_value", [np.nan, -1])
  def test_nan_euclidean_distances_one_feature_match_positive(missing_value):
      # First feature is the only feature that is non-nan and in both
      # samples. The result of `nan_euclidean_distances` with squared=True
      # should be non-negative. The non-squared version should all be close to 0.
      X = np.array([[-122.27, 648., missing_value, 37.85],
                    [-122.27, missing_value, 2.34701493, missing_value]])
  
      dist_squared = nan_euclidean_distances(X, missing_values=missing_value,
                                             squared=True)
      assert np.all(dist_squared >= 0)
  
      dist = nan_euclidean_distances(X, missing_values=missing_value,
                                     squared=False)
      assert_allclose(dist, 0.0)
  
  
  def test_cosine_distances():
      # Check the pairwise Cosine distances computation
      rng = np.random.RandomState(1337)
      x = np.abs(rng.rand(910))
      XA = np.vstack([x, x])
      D = cosine_distances(XA)
      assert_array_almost_equal(D, [[0., 0.], [0., 0.]])
      # check that all elements are in [0, 2]
      assert np.all(D >= 0.)
      assert np.all(D <= 2.)
      # check that diagonal elements are equal to 0
      assert_array_almost_equal(D[np.diag_indices_from(D)], [0., 0.])
  
      XB = np.vstack([x, -x])
      D2 = cosine_distances(XB)
      # check that all elements are in [0, 2]
      assert np.all(D2 >= 0.)
      assert np.all(D2 <= 2.)
      # check that diagonal elements are equal to 0 and non diagonal to 2
      assert_array_almost_equal(D2, [[0., 2.], [2., 0.]])
  
      # check large random matrix
      X = np.abs(rng.rand(1000, 5000))
      D = cosine_distances(X)
      # check that diagonal elements are equal to 0
      assert_array_almost_equal(D[np.diag_indices_from(D)], [0.] * D.shape[0])
      assert np.all(D >= 0.)
      assert np.all(D <= 2.)
  
  
  def test_haversine_distances():
      # Check haversine distance with distances computation
      def slow_haversine_distances(x, y):
          diff_lat = y[0] - x[0]
          diff_lon = y[1] - x[1]
          a = np.sin(diff_lat / 2) ** 2 + (
              np.cos(x[0]) * np.cos(y[0]) * np.sin(diff_lon/2) ** 2
          )
          c = 2 * np.arcsin(np.sqrt(a))
          return c
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 2))
      Y = rng.random_sample((10, 2))
      D1 = np.array([[slow_haversine_distances(x, y) for y in Y] for x in X])
      D2 = haversine_distances(X, Y)
      assert_array_almost_equal(D1, D2)
      # Test haversine distance does not accept X where n_feature != 2
      X = rng.random_sample((10, 3))
      err_msg = "Haversine distance only valid in 2 dimensions"
      with pytest.raises(ValueError, match=err_msg):
          haversine_distances(X)
  
  
  # Paired distances
  
  def test_paired_euclidean_distances():
      # Check the paired Euclidean distances computation
      X = [[0], [0]]
      Y = [[1], [2]]
      D = paired_euclidean_distances(X, Y)
      assert_array_almost_equal(D, [1., 2.])
  
  
  def test_paired_manhattan_distances():
      # Check the paired manhattan distances computation
      X = [[0], [0]]
      Y = [[1], [2]]
      D = paired_manhattan_distances(X, Y)
      assert_array_almost_equal(D, [1., 2.])
  
  
  def test_chi_square_kernel():
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((10, 4))
      K_add = additive_chi2_kernel(X, Y)
      gamma = 0.1
      K = chi2_kernel(X, Y, gamma=gamma)
      assert K.dtype == np.float
      for i, x in enumerate(X):
          for j, y in enumerate(Y):
              chi2 = -np.sum((x - y) ** 2 / (x + y))
              chi2_exp = np.exp(gamma * chi2)
              assert_almost_equal(K_add[i, j], chi2)
              assert_almost_equal(K[i, j], chi2_exp)
  
      # check diagonal is ones for data with itself
      K = chi2_kernel(Y)
      assert_array_equal(np.diag(K), 1)
      # check off-diagonal is < 1 but > 0:
      assert np.all(K > 0)
      assert np.all(K - np.diag(np.diag(K)) < 1)
      # check that float32 is preserved
      X = rng.random_sample((5, 4)).astype(np.float32)
      Y = rng.random_sample((10, 4)).astype(np.float32)
      K = chi2_kernel(X, Y)
      assert K.dtype == np.float32
  
      # check integer type gets converted,
      # check that zeros are handled
      X = rng.random_sample((10, 4)).astype(np.int32)
      K = chi2_kernel(X, X)
      assert np.isfinite(K).all()
      assert K.dtype == np.float
  
      # check that kernel of similar things is greater than dissimilar ones
      X = [[.3, .7], [1., 0]]
      Y = [[0, 1], [.9, .1]]
      K = chi2_kernel(X, Y)
      assert K[0, 0] > K[0, 1]
      assert K[1, 1] > K[1, 0]
  
      # test negative input
      with pytest.raises(ValueError):
          chi2_kernel([[0, -1]])
      with pytest.raises(ValueError):
          chi2_kernel([[0, -1]], [[-1, -1]])
      with pytest.raises(ValueError):
          chi2_kernel([[0, 1]], [[-1, -1]])
  
      # different n_features in X and Y
      with pytest.raises(ValueError):
          chi2_kernel([[0, 1]], [[.2, .2, .6]])
  
      # sparse matrices
      with pytest.raises(ValueError):
          chi2_kernel(csr_matrix(X), csr_matrix(Y))
      with pytest.raises(ValueError):
          additive_chi2_kernel(csr_matrix(X), csr_matrix(Y))
  
  
  @pytest.mark.parametrize(
          'kernel',
          (linear_kernel, polynomial_kernel, rbf_kernel,
           laplacian_kernel, sigmoid_kernel, cosine_similarity))
  def test_kernel_symmetry(kernel):
      # Valid kernels should be symmetric
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      K = kernel(X, X)
      assert_array_almost_equal(K, K.T, 15)
  
  
  @pytest.mark.parametrize(
          'kernel',
          (linear_kernel, polynomial_kernel, rbf_kernel,
           laplacian_kernel, sigmoid_kernel, cosine_similarity))
  def test_kernel_sparse(kernel):
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      X_sparse = csr_matrix(X)
      K = kernel(X, X)
      K2 = kernel(X_sparse, X_sparse)
      assert_array_almost_equal(K, K2)
  
  
  def test_linear_kernel():
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      K = linear_kernel(X, X)
      # the diagonal elements of a linear kernel are their squared norm
      assert_array_almost_equal(K.flat[::6], [linalg.norm(x) ** 2 for x in X])
  
  
  def test_rbf_kernel():
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      K = rbf_kernel(X, X)
      # the diagonal elements of a rbf kernel are 1
      assert_array_almost_equal(K.flat[::6], np.ones(5))
  
  
  def test_laplacian_kernel():
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      K = laplacian_kernel(X, X)
      # the diagonal elements of a laplacian kernel are 1
      assert_array_almost_equal(np.diag(K), np.ones(5))
  
      # off-diagonal elements are < 1 but > 0:
      assert np.all(K > 0)
      assert np.all(K - np.diag(np.diag(K)) < 1)
  
  
  @pytest.mark.parametrize('metric, pairwise_func',
                           [('linear', linear_kernel),
                            ('cosine', cosine_similarity)])
  def test_pairwise_similarity_sparse_output(metric, pairwise_func):
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((3, 4))
      Xcsr = csr_matrix(X)
      Ycsr = csr_matrix(Y)
  
      # should be sparse
      K1 = pairwise_func(Xcsr, Ycsr, dense_output=False)
      assert issparse(K1)
  
      # should be dense, and equal to K1
      K2 = pairwise_func(X, Y, dense_output=True)
      assert not issparse(K2)
      assert_array_almost_equal(K1.todense(), K2)
  
      # show the kernel output equal to the sparse.todense()
      K3 = pairwise_kernels(X, Y=Y, metric=metric)
      assert_array_almost_equal(K1.todense(), K3)
  
  
  def test_cosine_similarity():
      # Test the cosine_similarity.
  
      rng = np.random.RandomState(0)
      X = rng.random_sample((5, 4))
      Y = rng.random_sample((3, 4))
      Xcsr = csr_matrix(X)
      Ycsr = csr_matrix(Y)
  
      for X_, Y_ in ((X, None), (X, Y),
                     (Xcsr, None), (Xcsr, Ycsr)):
          # Test that the cosine is kernel is equal to a linear kernel when data
          # has been previously normalized by L2-norm.
          K1 = pairwise_kernels(X_, Y=Y_, metric="cosine")
          X_ = normalize(X_)
          if Y_ is not None:
              Y_ = normalize(Y_)
          K2 = pairwise_kernels(X_, Y=Y_, metric="linear")
          assert_array_almost_equal(K1, K2)
  
  
  def test_check_dense_matrices():
      # Ensure that pairwise array check works for dense matrices.
      # Check that if XB is None, XB is returned as reference to XA
      XA = np.resize(np.arange(40), (5, 8))
      XA_checked, XB_checked = check_pairwise_arrays(XA, None)
      assert XA_checked is XB_checked
      assert_array_equal(XA, XA_checked)
  
  
  def test_check_XB_returned():
      # Ensure that if XA and XB are given correctly, they return as equal.
      # Check that if XB is not None, it is returned equal.
      # Note that the second dimension of XB is the same as XA.
      XA = np.resize(np.arange(40), (5, 8))
      XB = np.resize(np.arange(32), (4, 8))
      XA_checked, XB_checked = check_pairwise_arrays(XA, XB)
      assert_array_equal(XA, XA_checked)
      assert_array_equal(XB, XB_checked)
  
      XB = np.resize(np.arange(40), (5, 8))
      XA_checked, XB_checked = check_paired_arrays(XA, XB)
      assert_array_equal(XA, XA_checked)
      assert_array_equal(XB, XB_checked)
  
  
  def test_check_different_dimensions():
      # Ensure an error is raised if the dimensions are different.
      XA = np.resize(np.arange(45), (5, 9))
      XB = np.resize(np.arange(32), (4, 8))
      with pytest.raises(ValueError):
          check_pairwise_arrays(XA, XB)
  
      XB = np.resize(np.arange(4 * 9), (4, 9))
      with pytest.raises(ValueError):
          check_paired_arrays(XA, XB)
  
  
  def test_check_invalid_dimensions():
      # Ensure an error is raised on 1D input arrays.
      # The modified tests are not 1D. In the old test, the array was internally
      # converted to 2D anyways
      XA = np.arange(45).reshape(9, 5)
      XB = np.arange(32).reshape(4, 8)
      with pytest.raises(ValueError):
          check_pairwise_arrays(XA, XB)
      XA = np.arange(45).reshape(9, 5)
      XB = np.arange(32).reshape(4, 8)
      with pytest.raises(ValueError):
          check_pairwise_arrays(XA, XB)
  
  
  def test_check_sparse_arrays():
      # Ensures that checks return valid sparse matrices.
      rng = np.random.RandomState(0)
      XA = rng.random_sample((5, 4))
      XA_sparse = csr_matrix(XA)
      XB = rng.random_sample((5, 4))
      XB_sparse = csr_matrix(XB)
      XA_checked, XB_checked = check_pairwise_arrays(XA_sparse, XB_sparse)
      # compare their difference because testing csr matrices for
      # equality with '==' does not work as expected.
      assert issparse(XA_checked)
      assert abs(XA_sparse - XA_checked).sum() == 0
      assert issparse(XB_checked)
      assert abs(XB_sparse - XB_checked).sum() == 0
  
      XA_checked, XA_2_checked = check_pairwise_arrays(XA_sparse, XA_sparse)
      assert issparse(XA_checked)
      assert abs(XA_sparse - XA_checked).sum() == 0
      assert issparse(XA_2_checked)
      assert abs(XA_2_checked - XA_checked).sum() == 0
  
  
  def tuplify(X):
      # Turns a numpy matrix (any n-dimensional array) into tuples.
      s = X.shape
      if len(s) > 1:
          # Tuplify each sub-array in the input.
          return tuple(tuplify(row) for row in X)
      else:
          # Single dimension input, just return tuple of contents.
          return tuple(r for r in X)
  
  
  def test_check_tuple_input():
      # Ensures that checks return valid tuples.
      rng = np.random.RandomState(0)
      XA = rng.random_sample((5, 4))
      XA_tuples = tuplify(XA)
      XB = rng.random_sample((5, 4))
      XB_tuples = tuplify(XB)
      XA_checked, XB_checked = check_pairwise_arrays(XA_tuples, XB_tuples)
      assert_array_equal(XA_tuples, XA_checked)
      assert_array_equal(XB_tuples, XB_checked)
  
  
  def test_check_preserve_type():
      # Ensures that type float32 is preserved.
      XA = np.resize(np.arange(40), (5, 8)).astype(np.float32)
      XB = np.resize(np.arange(40), (5, 8)).astype(np.float32)
  
      XA_checked, XB_checked = check_pairwise_arrays(XA, None)
      assert XA_checked.dtype == np.float32
  
      # both float32
      XA_checked, XB_checked = check_pairwise_arrays(XA, XB)
      assert XA_checked.dtype == np.float32
      assert XB_checked.dtype == np.float32
  
      # mismatched A
      XA_checked, XB_checked = check_pairwise_arrays(XA.astype(np.float),
                                                     XB)
      assert XA_checked.dtype == np.float
      assert XB_checked.dtype == np.float
  
      # mismatched B
      XA_checked, XB_checked = check_pairwise_arrays(XA,
                                                     XB.astype(np.float))
      assert XA_checked.dtype == np.float
      assert XB_checked.dtype == np.float
  
  
  @pytest.mark.parametrize("n_jobs", [1, 2])
  @pytest.mark.parametrize("metric", ["seuclidean", "mahalanobis"])
  @pytest.mark.parametrize("dist_function",
                           [pairwise_distances, pairwise_distances_chunked])
  @pytest.mark.parametrize("y_is_x", [True, False], ids=["Y is X", "Y is not X"])
  def test_pairwise_distances_data_derived_params(n_jobs, metric, dist_function,
                                                  y_is_x):
      # check that pairwise_distances give the same result in sequential and
      # parallel, when metric has data-derived parameters.
      with config_context(working_memory=0.1):  # to have more than 1 chunk
          rng = np.random.RandomState(0)
          X = rng.random_sample((100, 10))
  
          if y_is_x:
              Y = X
              expected_dist_default_params = squareform(pdist(X, metric=metric))
              if metric == "seuclidean":
                  params = {'V': np.var(X, axis=0, ddof=1)}
              else:
                  params = {'VI': np.linalg.inv(np.cov(X.T)).T}
          else:
              Y = rng.random_sample((100, 10))
              expected_dist_default_params = cdist(X, Y, metric=metric)
              if metric == "seuclidean":
                  params = {'V': np.var(np.vstack([X, Y]), axis=0, ddof=1)}
              else:
                  params = {'VI': np.linalg.inv(np.cov(np.vstack([X, Y]).T)).T}
  
          expected_dist_explicit_params = cdist(X, Y, metric=metric, **params)
          dist = np.vstack(tuple(dist_function(X, Y,
                                               metric=metric, n_jobs=n_jobs)))
  
          assert_allclose(dist, expected_dist_explicit_params)
          assert_allclose(dist, expected_dist_default_params)
  
apis: sklearn.metrics.pairwise.PAIRED_DISTANCES.items scipy.spatial.distance.pdist numpy.ones scipy.spatial.distance.cdist numpy.sum scipy.sparse.dok_matrix sklearn.metrics.pairwise.check_paired_arrays sklearn.metrics.pairwise.cosine_distances sklearn.metrics.pairwise.haversine_distances numpy.diag sklearn.metrics.pairwise.laplacian_kernel numpy.var sklearn.metrics.pairwise.pairwise_distances numpy.random.RandomState sklearn.config_context numpy.full sklearn.metrics.pairwise.pairwise_distances_chunked sklearn.metrics.pairwise.pairwise_kernels numpy.isfinite numpy.cov numpy.testing.assert_almost_equal numpy.vstack sklearn.metrics.pairwise._euclidean_distances_upcast sklearn.utils._testing.assert_array_equal sklearn.metrics.pairwise.euclidean_distances numpy.abs numpy.cos sklearn.metrics.pairwise.chi2_kernel sklearn.metrics.pairwise.rbf_kernel sklearn.preprocessing.normalize sklearn.metrics.pairwise.pairwise_distances_argmin_min numpy.isnan sklearn.utils._testing.assert_array_almost_equal numpy.sqrt numpy.atleast_2d sklearn.metrics.pairwise.manhattan_distances numpy.zeros sklearn.utils._testing.assert_allclose numpy.arange numpy.diag_indices_from numpy.all sklearn.utils._testing.ignore_warnings sklearn.metrics.pairwise.paired_manhattan_distances sklearn.metrics.pairwise.additive_chi2_kernel numpy.maximum numpy.linalg.norm numpy.zeros_like sklearn.metrics.pairwise.nan_euclidean_distances sklearn.metrics.pairwise.paired_distances scipy.sparse.issparse sklearn.metrics.pairwise.pairwise_distances_argmin sklearn.utils._testing.assert_almost_equal scipy.sparse.csr_matrix numpy.exp sklearn.metrics.pairwise.linear_kernel sklearn.metrics.pairwise.check_pairwise_arrays numpy.array numpy.sin numpy.concatenate sklearn.metrics.pairwise.paired_euclidean_distances