code: def triu_reference_implementation(x, k=0):  # type: ignore
      return np.triu(x, k)
  
imports: import numpy
  import onnx
  from onnx.backend.test.case.base import Base
  from onnx.backend.test.case.node import expect
label_desc: Use image node_id 1 for calling a global function with example usage: triu_reference_implementation(x, k) and returns: np