code: def pca_pos(data4d):
      """Flips signs equal over volume for PCA
  
      Needed because Windows appears to generate random signs for PCA components
      across PCA runs on the same data.
      """
      signs = np.sign(data4d[0, 0, 0, :])
      return data4d * signs
  
imports: import os
  from os.path import join
  from warnings import catch_warnings, simplefilter
  import numpy
  import pytest
  from numpy.testing import assert_almost_equal, assert_array_equal
  import nipy
  from nipy.core.api import rollimg
  from nipy.testing import funcfile
  from nipy.testing.decorators import needs_mpl_agg
  from ...utils.pca import pca
  from ...utils.tests.test_pca import res2pos1
  from ..screens import screen, write_screen_res
  from ..timediff import time_slice_diffs
label_desc: Use image node_id 4 for calling a global function with example usage: pca_pos(data4d) and returns: unknown