tensor_en (#603)

* tensor_en

* Review

* file path

doc/fluid/api_guides/low_level/layers/tensor_en.rst

+.. _api_guide_tensor_en:
+
+########
+Tensor
+########
+
+There are two data structures used in Fluid to host the data, namely `Tensor and LoD_Tensor <../../../user_guides/howto/prepare_data/lod_tensor_en.html>`_. LoD-Tensor is a unique concept of Fluid, which appends sequence information to Tensor. The data that can be transferred in the framework includes: input, output, and learnable parameters in the network. All of them are uniformly represented by LoD-Tensor. In addition, tensor can be regarded as a special LoD-Tensor.
+
+Now let's take a closer look at the operations related to these two types of data.
+
+Tensor
+=======
+
+1. create_tensor
+---------------------
+Tensor is used to carry data in the framework, using :code:`create_tensor` to create a Lod-Tensor variable of the specified the data type.
+
+API reference : :ref:`api_fluid_layers_create_tensor`
+
+
+2. create_parameter
+---------------------
+The neural network training process is a learning process for parameters. Fluid uses :code:`create_parameter` to create a learnable parameter. The value of this parameter can be changed by the operator.
+
+API reference  : :ref:`api_fluid_layers_create_parameter`
+
+
+
+3. create_global_var
+---------------------
+Fluid uses :code:`create_global_var` to create a global tensor and this API allows you to specify the data type, shape, and value of the Tensor variable being created.
+
+API reference  : :ref:`api_fluid_layers_create_global_var`
+
+
+4. cast
+---------------
+
+Fluid uses :code:`cast` to convert the data to the specified type.
+
+API reference  : :ref:`api_fluid_layers_cast`
+
+
+5.concat
+----------------
+
+Fluid uses :code:`concat` to concatenate input data along a specified dimension.
+
+API reference  : :ref:`api_fluid_layers_concat`
+
+
+6. sums
+----------------
+
+Fluid uses :code:`sums` to sum up the input data.
+
+API reference  : :ref:`api_fluid_layers_sums`
+
+
+7. fill_constant_batch_size_like
+---------------------------------
+
+Fluid uses :code:`fill_constant_batch_size_like` to create a Tensor with a specific shape, type, and batch_size. And the initial value of the Tensor can be specified as an arbitrary constant. The batch_size information is determined by the tensor's :code:`input_dim_idx` and :code:`output_dim_idx`.
+
+API reference  : :ref:`api_fluid_layers_fill_constant_batch_size_like`
+
+8. fill_constant
+-----------------
+
+Fluid uses :code:`fill_constant` to create a Tensor with a specific shape and type. The initial value of this variable can be set via :code:`value`.
+
+API reference : :ref:`api_fluid_layers_fill_constant`
+
+9. assign
+---------------
+
+Fluid uses :code:`assign` to duplicate a variable.
+
+API reference  : :ref:`api_fluid_layers_assign`
+
+10. argmin
+--------------
+
+Fluid uses :code:`argmin` to calculate the index of the smallest element on the specified axis of Tensor.
+
+API reference  : :ref:`api_fluid_layers_argmin`
+
+11. argmax
+-----------
+
+Fluid uses :code:`argmax` to calculate the index of the largest element on the specified axis of Tensor.
+
+API reference  : :ref:`api_fluid_layers_argmax`
+
+12. argsort
+------------
+
+Fluid uses :code:`argsort` to sort the input Tensor on the specified axis and it will return the sorted data variables and their corresponding index values.
+
+API reference : :ref:`api_fluid_layers_argsort`
+
+13. ones
+-------------
+
+Fluid uses :code:`ones` to create a Tensor of the specified size and data type with an initial value of 1.
+
+API reference : :ref:`api_fluid_layers_ones`
+
+14. zeros
+---------------
+
+Fluid uses :code:`zeros` to create a Tensor of the specified size and data type with an initial value of zero.
+
+API reference : :ref:`api_fluid_layers_zeros`
+
+15. reverse
+-------------------
+
+Fluid uses :code:`reverse` to invert Tensor along the specified axis.
+
+API reference : :ref:`api_fluid_layers_reverse`
+
+
+
+LoD-Tensor
+============
+
+LoD-Tensor is very suitable for sequence data. For related knowledge, please read `LoD_Tensor <../../../user_guides/howto/prepare_data/lod_tensor_en.html>`_.
+
+1.create_lod_tensor
+-----------------------
+
+Fluid uses :code:`create_lod_tensor` to create a LoD_Tensor with new hierarchical information based on a numpy array, a list, or an existing LoD_Tensor.
+
+API reference : :ref:`api_fluid_create_lod_tensor`
+
+2. create_random_int_lodtensor
+----------------------------------
+
+Fluid uses :code:`create_random_int_lodtensor` to create a LoD_Tensor composed of random integers.
+
+API reference : :ref:`api_fluid_create_random_int_lodtensor`
+
+3. reorder_lod_tensor_by_rank
+---------------------------------
+
+Fluid uses :code:`reorder_lod_tensor_by_rank` to reorder the sequence information of the input LoD_Tensor in the specified order.
+
+API reference : :ref:`api_fluid_layers_reorder_lod_tensor_by_rank`
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