code: def upper_hemi_map(v):
      """
      maps a 3-vector into the z-upper hemisphere
      """
      return np.sign(v[2]) * v
  
imports: import numpy
  from dipy.reconst.odf import OdfModel, OdfFit
  from dipy.reconst.cache import Cache
  import warnings
  from dipy.reconst.multi_voxel import multi_voxel_fit
label_desc: Use image node_id 6 for calling a global function with example usage: upper_hemi_map(v) and returns: unknown