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From GitBox <...@apache.org>
Subject [GitHub] [incubator-mxnet] IvyBazan commented on a change in pull request #15517: Tensor Inspector Tutorial
Date Fri, 19 Jul 2019 00:55:55 GMT
IvyBazan commented on a change in pull request #15517: Tensor Inspector Tutorial
URL: https://github.com/apache/incubator-mxnet/pull/15517#discussion_r305163728
 
 

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 File path: docs/faq/tensor_inspector_tutorial.md
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+
+# Use TensorInspector to Help Debug Operators
+
+## Introduction
+
+When developing new operators, developers need to deal with tensor objects extensively. This
new utility, Tensor Inspector, mainly aims to help developers debug by providing unified interfaces
to print, check, and dump the tensor value. To developers' convenience, this utility works
for all the three data types: Tensors, TBlobs, and NDArrays. Also, it supports both CPU and
GPU tensors.
+
+
+## Usage 
+
+This utility is located in `src/common/tensor_inspector.h`. To use it in any operator code,
just include `tensor_inspector`, construct an `TensorInspector` object, and call the APIs
on that object. You can run any script that uses the operator you just modified then.
+
+The screenshot below shows a sample usage in `src/operator/nn/convolution-inl.h`.
+
+![Screen Shot 2019-07-08 at 5 03 46 PM](https://user-images.githubusercontent.com/16669457/60850062-68690e00-a1a2-11e9-8268-033edde17aa4.png)
+
+
+## Functionalities/APIs
+
+### Create a TensorInspector Object from Tensor, TBlob, and NDArray Objects
+
+You can create a `TensorInspector` object by passing in two things: 1) an object of type
`Tensor`, `Tbob`, or `NDArray`, and 2) an `RunContext` object.
+
+Essentially, `TensorInspector` can be understood as a wrapper class around `TBlob`. Internally,
the `Tensor`, `Tbob`, or `NDArray` object that you passed in will be converted to a `TBlob`
object. The `RunContext` object is used when the the tensor is a GPU tensor; in such a case,
we need to use the context information to copy the data from GPU memory to CPU/main memory.
+
+Below are the three constructors:
+
+```c++
+// Construct from Tensor object
+template<typename Device, int dimension, typename DType MSHADOW_DEFAULT_DTYPE>
+TensorInspector(const  mshadow::Tensor<Device, dimension, DType>& ts, const RunContext&
ctx);
+
+// Construct from TBlob object
+TensorInspector(const TBlob& tb, const RunContext& ctx);
+
+// Construct from NDArray object
+TensorInspector(const NDArray& arr, const RunContext& ctx):
+```
+
+### Print Tensor Value (Static) 
+
+To print out the tensor value in a nicely structured way,  you can use this API:
+
+```c++
+void print_string();
+```
+
+This API will print the entire tensor to `std::cout` and preserve the shape (it supports
all dimensions from 1 and up). You can copy the output and interpret it with any `JSON` loader.
Also, on the last line of the output you can find some useful information about the tensor.
Refer to the case below, we are able to know that this is a float-typed tensor with shape
20x1x5x5.
 
 Review comment:
   Suggested edit for clarity and flow: "You can find some useful information about the tensor
on the last line of the output."

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