class_docstr: Points on the unit sphere.
  
  The sphere can be constructed using one of three conventions::
  
    Sphere(x, y, z)
    Sphere(xyz=xyz)
    Sphere(theta=theta, phi=phi)
  
  Parameters
  ----------
  x, y, z : 1-D array_like
      Vertices as x-y-z coordinates.
  theta, phi : 1-D array_like
      Vertices as spherical coordinates.  Theta and phi are the inclination
      and azimuth angles respectively.
  xyz : (N, 3) ndarray
      Vertices as x-y-z coordinates.
  faces : (N, 3) ndarray
      Indices into vertices that form triangular faces.  If unspecified,
      the faces are computed using a Delaunay triangulation.
  edges : (N, 2) ndarray
      Edges between vertices.  If unspecified, the edges are
      derived from the faces.
docstr: Find the index of the vertex in the Sphere closest to the input vector
  
  Parameters
  ----------
  xyz : array-like, 3 elements
      A unit vector
  
  Returns
  -------
  idx : int
      The index into the Sphere.vertices array that gives the closest
      vertex (in angle).
code: def find_closest(self, xyz):
      """
      Find the index of the vertex in the Sphere closest to the input vector
  
      Parameters
      ----------
      xyz : array-like, 3 elements
          A unit vector
  
      Returns
      -------
      idx : int
          The index into the Sphere.vertices array that gives the closest
          vertex (in angle).
      """
      cos_sim = np.dot(self.vertices, xyz)
      return np.argmax(cos_sim)
  
imports: import numpy
  import warnings
  from scipy import optimize
  from dipy.core.geometry import cart2sphere, sphere2cart, vector_norm
  from dipy.core.onetime import auto_attr
  from dipy.reconst.recspeed import remove_similar_vertices
label_desc: Use image node_id 9 for calling the Sphere obj's underlying member method code with example usage: obj.find_closest(xyz) and returns: np