code: def ref_selu(x, scale, alpha):
      return np.where(x > 0, scale * x, scale * alpha * (np.exp(x) - 1))
  
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_selu(x, scale, alpha) and returns: np