message: Register gradient for argmin (cf.
diff: @@ -41,6 +41,12 @@ def _ArgMaxGrad(op, grad):
  return [None, None]
  +@ops.RegisterGradient("ArgMin")
  +def _ArgMinGrad(op, grad):
  + del op, grad
  + return [None, None]
  +
  +
  @ops.RegisterGradient("Sum")
  def _SumGrad(op, grad):
  """Gradient for Sum."""
  