code: def ref_func_sign(x, alpha):
      # returns -1 if x < 0, alpha if x==0, 1 if x > 0.
      y = np.sign(x)
      y[x == 0] = alpha
      return y
  
file_path: nnabla/python/test/function/test_sign.py
imports: import pytest
  import numpy
  import nnabla.functions
  from nbla_test_utils import list_context
label_desc: Use image node_id 1 for calling a global function with example usage: ref_func_sign(x, alpha) and returns: y