code: def mapping(x, y, z):
      return 2 * x, y, 0.5 * z
  
file_path: nipy/nipy/labs/datasets/volumes/tests/test_volume_grid.py
imports: import copy
  import numpy
  import pytest
  from ...transforms.transform import CompositionError, Transform
  from ..volume_grid import VolumeGrid
  from ..volume_img import VolumeImg
label_desc: Use image node_id 1 for calling a global function with example usage: mapping(x, y, z) and returns: unknown,  y,  unknown