code: def _equality_constraints(vects):
      """Spherical equality constraint. Returns 0 if vects lies on the unit
      sphere. Note that a flattened array is returned because `scipy.optimize`
      expects a 1-D array.
  
      Parameters
      ----------
      vects : array-like shape (N * 3)
          Points on the sphere.
      Returns
      -------
      array-like (N,)
          Difference between squared vector norms and 1.
  
      """
  
      N = vects.shape[0] // 3
      vects = vects.reshape((N, 3))
      return (vects**2).sum(1) - 1.0
  
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 10 for calling a global function with example usage: _equality_constraints(vects) and returns: unknown