Thanks for your replies.
And I would like to know where is overriding apply method for these operator

  
      github.com
  
  
    pytorch/pytorch/blob/e87f77def637edf85aa5191f8422892415e4f5ae/torch/csrc/autograd/function.h#L39-L46

///~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
///                               Function
///~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/// A `Function` is an abstract class that represents an operation taking zero
/// or more input `Variable`s and producing zero or more output `Variable`s. All
/// functions in PyTorch's autograd machinery derive from this class and
/// override its `apply` method. Instances of such subclasses will then be
/// invokeable via the call operator.