[GitHub] II-Matto opened a new issue #9012: Implementing New Operators

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II-Matto opened a new issue #9012: Implementing New Operators
URL: https://github.com/apache/incubator-mxnet/issues/9012
 
 
   I would like to implement a new operator with MXNet, and the operator is already implemented with Caffe. What is the easiest way to port my Caffe implementation to MXNet?
   
   The comment https://github.com/apache/incubator-mxnet/issues/7652#issuecomment-325894475 says that it is easier to implement complex operators using the legacy interface. But will the **legacy interface** be unsupported in the future? If it is OK to use the legacy interface, can someone provide links to some **comprehensive tutorials or examples**?
   
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   To use the new nnvm interface for defining operators, I read this document: [A Beginner's Guide to Implementing Operators in MXNet Backend](https://github.com/apache/incubator-mxnet/blob/master/docs/how_to/add_op_in_backend.md). The step-by-step explanations are clear and I have understood the general pipeline of defining a new operator, but there still seems to be some obstacles in the way.
   
   1. How can I define **_variables storing intermediate results_** which can be used in both forward and backward computations? These variables will act like class member variables (assuming the operator is defined as a class). This is similar to the question in the comment https://github.com/apache/incubator-mxnet/issues/7652#issuecomment-338910634.
   2. How can I define a _**operator with learnable parameters**_ (e.g. convolution operator)? The current implementations of operators such as convolution seem to use a different (and legacy) interface. And the [tensor examples](https://github.com/apache/incubator-mxnet/tree/master/src/operator/tensor) are all parameter-free operators like dot product.
   3. Where can I find _**explanations of the various macros**_ to be used in operator definitions? The many macros are very confusing and it is hard for me to determine when I should use what and how. It would be very helpful if some templates for typical usages can be provided and explained.
   4. How can I **_correctly reference the headers_** in [src/operator](https://github.com/apache/incubator-mxnet/tree/master/src/operator), if I put my operator definition files in an independent directory outside MXNet? Many source files simply use relative paths, e.g. `#include #include "../mxnet_op.h"` and `#include "../mshadow_op.h"`, which are not suitable if a file is located outside MXNet directories.
   5. How can I **_specify multiple paths for the_** `EXTRA_OPERATORS` in  [config.mk](https://github.com/apache/incubator-mxnet/blob/master/make/config.mk)? After checking the [Makefile](https://github.com/apache/incubator-mxnet/blob/master/Makefile) and [CMakeLists.txt](https://github.com/apache/incubator-mxnet/blob/master/CMakeLists.txt), I find that only one path is supported (Please correct me if I am wrong).

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