adaptiveAveragePooling2dLayer

R2026b

Adaptive average pooling 2-D layer

Since R2024a

Description

A 2-D adaptive average pooling layer performs downsampling to give you the desired output size by dividing the input into rectangular pooling regions, then computing the average of each region.

Creation

Syntax

layer = adaptiveAveragePooling2dLayer(outputSize)

layer = adaptiveAveragePooling2dLayer(outputSize,Name=name)

Description

layer = adaptiveAveragePooling2dLayer(outputSize) creates an adaptive average pooling layer and sets the OutputSize property.

layer = adaptiveAveragePooling2dLayer(outputSize,Name=name) also sets the optional Name property. For example, adaptiveAveragePooling2dLayer(16,Name="adap") creates an adaptive average pooling layer with an output size of [16 16] and sets the name to "adap".

Input Arguments

outputSize — Output size

positive integer | vector of two positive integers

Output size, specified as one of these:

• Positive integer sz — Output data of size of [sz sz].

• Vector of two positive integers [sz1 sz2] — Output data of size [sz1 sz2].

This argument sets the OutputSize property.

Example: [12 14] specifies output size of 12 and 14 for the lengths of first and second dimensions respectively.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

name — Layer name

"" (default) | character vector | string scalar

Layer name, specified as a character vector or a string scalar. For Layer array input, the trainnet and dlnetwork functions automatically assign names to unnamed layers.

This argument sets the Name property.

Data Types: char | string

Properties

Adaptive Average Pooling

OutputSize — Output size

vector of two positive integers

Output size, specified as a vector of two positive integers.

When you set this property, you can also specify a scalar value to use the same value for both dimensions.

Data Types: double

Layer

Name — Layer name

'' (default) | character vector

Layer name, specified as a character vector. For Layer array input, the trainnet and dlnetwork functions automatically assign names to unnamed layers.

Data Types: char

NumInputs — Number of inputs

Read-only: 1 (default)

This property is read-only.

Number of inputs to the layer, represented as 1. This layer has a single input only.

Data Types: double

InputNames — Input name

Read-only: {'in'} (default)

This property is read-only.

Input name, represented as {'in'}. This layer has a single input only.

NumOutputs — Number of outputs

Read-only: 1 (default)

This property is read-only.

Number of outputs from the layer, represented as 1. This layer has a single output only.

Data Types: double

OutputNames — Output name

Read-only: {'out'} (default)

This property is read-only.

Output name, represented as {'out'}. This layer has a single output only.

Examples

Create Adaptive Average Pooling Layer

Create an adaptive average pooling layer with the output size [12 12] name "adap_avg1".

layer = adaptiveAveragePooling2dLayer(12,Name="adap_avg1")

layer = 
  AdaptiveAveragePooling2DLayer with properties:

          Name: 'adap_avg1'
    OutputSize: [12 12]

   Learnable Parameters
    No properties.

   State Parameters
    No properties.

  Show all properties

Include an adaptive average pooling layer with the output size [12 12] in a Layer array. The layer automatically selects the stride and kernel-size to give you the specified output size.

layers = [ ...
    imageInputLayer([28 28 1])
    convolution2dLayer(5,20)
    reluLayer
    adaptiveAveragePooling2dLayer(12)
    fullyConnectedLayer(10)
    softmaxLayer]

layers = 
  6×1 Layer array with layers:

     1   ''   Image Input                    28×28×1 images with 'zerocenter' normalization
     2   ''   2-D Convolution                20 5×5 convolutions with stride [1  1] and padding [0  0  0  0]
     3   ''   ReLU                           ReLU
     4   ''   2-D Adaptive Average Pooling   Adaptive average pooling with output size 12x12
     5   ''   Fully Connected                Fully connected layer with output size 10
     6   ''   Softmax                        Softmax

Algorithms

2-D Adaptive Average Pooling Layer

A 2-D adaptive average pooling layer performs downsampling by dividing the input into rectangular pooling regions, then computing the average of each region.

The dimensions that the layer pools over depends on the layer input:

• For 2-D image input (data with four dimensions corresponding to pixels in two spatial dimensions, the channels, and the observations), the layer pools over the spatial dimensions.

• For 2-D image sequence input (data with five dimensions corresponding to the pixels in two spatial dimensions, the channels, the observations, and the time steps), the layer pools over the spatial dimensions.

• For 1-D image sequence input (data with four dimensions corresponding to the pixels in one spatial dimension, the channels, the observations, and the time steps), the layer pools over the spatial and time dimensions.

Layer Input and Output Formats

Most layers in a layer array or layer graph pass data to subsequent layers as formatted dlarray objects. The format of a dlarray object is a string of characters in which each character describes the corresponding dimension of the data. The format consists of one or more of these characters:

• "S" — Spatial

• "C" — Channel

• "B" — Batch

• "T" — Time

• "U" — Unspecified

For example, you can describe 2-D image data that is represented as a 4-D array, where the first two dimensions correspond to the spatial dimensions of the images, the third dimension corresponds to the channels of the images, and the fourth dimension corresponds to the batch dimension, as having the format "SSCB" (spatial, spatial, channel, batch).

You can interact with these dlarray objects in automatic differentiation workflows, such as those for:

• developing a custom layer

• using a functionLayer object

• using the forward and predict functions with dlnetwork objects

This table shows the supported input formats of AdaptiveAveragePooling2DLayer objects and the corresponding output format. If the software passes the output of the layer to a custom layer that does not inherit from the nnet.layer.Formattable class, or to a FunctionLayer object with the Formattable property set to 0 (false), then the layer receives an unformatted dlarray object with dimensions ordered according to the formats in this table. The formats listed here are only a subset of the formats that the layer supports. The layer might support additional formats, such as formats with additional "S" (spatial) or "U" (unspecified) dimensions.

Input Format	Output Format
"SSCB" (spatial, spatial, channel, batch)	"SSCB" (spatial, spatial, channel, batch)
"SCBT" (spatial, channel, batch, time)	"SCBT" (spatial, channel, batch, time)
"SSCBT" (spatial, spatial, channel, batch, time)	"SSCBT" (spatial, spatial, channel, batch, time)
"SSB" (spatial, spatial, batch)	"SSB" (spatial, spatial, batch)
"SSC" (spatial, spatial, channel)	"SSC" (spatial, spatial, channel)
"SCT" (spatial, channel, time)	"SCT" (spatial, channel, time)
"SSCT" (spatial, spatial, channel, time)	"SSCT" (spatial, spatial, channel, time)
"SBT" (spatial, batch, time)	"SBT" (spatial, batch, time)
"SSBT" (spatial, spatial, batch, time)	"SSBT" (spatial, spatial, batch, time)

References

[1] Nagi, J., F. Ducatelle, G. A. Di Caro, D. Ciresan, U. Meier, A. Giusti, F. Nagi, J. Schmidhuber, L. M. Gambardella. ''Max-Pooling Convolutional Neural Networks for Vision-based Hand Gesture Recognition''. IEEE International Conference on Signal and Image Processing Applications (ICSIPA2011), 2011.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Version History

Introduced in R2024a