flattenConcat Plugin [DEPRECATED]

This plugin is deprecated since TensorRT 10.12 and will be removed in a future release. IConcatenationLayer can be used as an alternative as appropriate to replace its functionality.

Table Of Contents

• Description
  • Structure
• Parameters
• Additional resources
• License
• Changelog
• Known issues

Description

The flattenConcat plugin performs input tensor flattening followed by concatenation in a single step. The SSD object detection model has bounding box predictions, including bounding box location predictions and object classifications, from different feature maps in the neural network. The bounding box location prediction tensors from different feature maps are flattened and concatenated into a single tensor, as well as the object classification tensors. Merging tensor flattening and concatenation into a single step accelerates the inference speed in TensorRT.

Structure

This plugin supports the NCHW format. It takes an arbitrary number of input tensors of shape [N, C_1, H, W], [N, C_2, H, W], ..., [N, C_k, H, W], flattens and concatenates these input tensors, and generates an output tensor of shape [N, C, 1, 1] where C = (C_1 + C_2 + ... + C_k) * H * W.

For example, you have input tensor A of shape [2, 2, 2, 2]:

[[[[ 0 1]
   [ 2 3]]

  [[ 4 5]
   [ 6 7]]]
  

 [[[ 8 9]
   [10 11]]

  [[12 13]
   [14 15]]]]

and input tensor B of shape [2, 3, 2, 2]:

[[[[16 17]
   [18 19]]

  [[20 21]
   [22 23]]
 
  [[24 25]
   [26 27]]]

 
 [[[28 29]
   [30 31]]

  [[32 33]
   [34 35]]

  [[36 37]
   [38 39]]]]

After flattenConcat for the two inputs, the output tensor of shape [2, 20, 1, 1] is:

[[[[ 0]]

  [[ 1]]

  [[ 2]]

  [[ 3]]

  [[ 4]]

  [[ 5]]

  [[ 6]]

  [[ 7]]

  [[16]]

  [[17]]

  [[18]]

  [[19]]

  [[20]]

  [[21]]

  [[22]]

  [[23]]

  [[24]]

  [[25]]

  [[26]]

  [[27]]]


 [[[ 8]]

  [[ 9]]

  [[10]]

  [[11]]

  [[12]]

  [[13]]

  [[14]]

  [[15]]

  [[28]]

  [[29]]

  [[30]]

  [[31]]

  [[32]]

  [[33]]

  [[34]]

  [[35]]

  [[36]]

  [[37]]

  [[38]]

  [[39]]]]

Parameters

This plugin has the plugin creator class FlattenConcatPluginCreator and the plugin class FlattenConcat.

The following parameters were used to create FlattenConcat instance:

Additional resources

The following resources provide a deeper understanding of the flattenConcat plugin:

• SSD Caffe Implementation

License

For terms and conditions for use, reproduction, and distribution, see the TensorRT Software License Agreement documentation.

Changelog

May 2025 Add deprecation note.

May 2019 This is the first release of this README.md file.

Known issues

There are no known issues in this plugin.