# averagePooling2dLayer

Average pooling layer

## Description

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

## Creation

### Syntax

``layer = averagePooling2dLayer(poolSize)``
``layer = averagePooling2dLayer(poolSize,Name,Value)``

### Description

````layer = averagePooling2dLayer(poolSize)` creates an average pooling layer and sets the `PoolSize` property.```

example

````layer = averagePooling2dLayer(poolSize,Name,Value)` sets the optional `Stride` and `Name` properties using name-value pairs. To specify input padding, use the `'Padding'` name-value pair argument. For example, `averagePooling2dLayer(2,'Stride',2)` creates an average pooling layer with pool size `[2 2]` and stride ```[2 2]```. You can specify multiple name-value pairs. Enclose each property name in single quotes.```

### Input Arguments

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Name-Value Arguments

Use comma-separated name-value pair arguments to specify the size of the zero padding to add along the edges of the layer input or to set the `Stride` and `Name` properties. Enclose names in single quotes.

Example: `averagePooling2dLayer(2,'Stride',2)` creates an average pooling layer with pool size `[2 2]` and stride `[2 2]`.

Input edge padding, specified as the comma-separated pair consisting of `'Padding'` and one of these values:

• `'same'` — Add padding of size calculated by the software at training or prediction time so that the output has the same size as the input when the stride equals 1. If the stride is larger than 1, then the output size is `ceil(inputSize/stride)`, where `inputSize` is the height or width of the input and `stride` is the stride in the corresponding dimension. The software adds the same amount of padding to the top and bottom, and to the left and right, if possible. If the padding that must be added vertically has an odd value, then the software adds extra padding to the bottom. If the padding that must be added horizontally has an odd value, then the software adds extra padding to the right.

• Nonnegative integer `p` — Add padding of size `p` to all the edges of the input.

• Vector `[a b]` of nonnegative integers — Add padding of size `a` to the top and bottom of the input and padding of size `b` to the left and right.

• Vector `[t b l r]` of nonnegative integers — Add padding of size `t` to the top, `b` to the bottom, `l` to the left, and `r` to the right of the input.

Example: `'Padding',1` adds one row of padding to the top and bottom, and one column of padding to the left and right of the input.

Example: `'Padding','same'` adds padding so that the output has the same size as the input (if the stride equals 1).

## Properties

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### Average Pooling

Dimensions of the pooling regions, specified as a vector of two positive integers `[h w]`, where `h` is the height and `w` is the width. When creating the layer, you can specify `PoolSize` as a scalar to use the same value for both dimensions.

If the stride dimensions `Stride` are less than the respective pooling dimensions, then the pooling regions overlap.

The padding dimensions `PaddingSize` must be less than the pooling region dimensions `PoolSize`.

Example: `[2 1]` specifies pooling regions of height 2 and width 1.

Step size for traversing the input vertically and horizontally, specified as a vector of two positive integers `[a b]`, where `a` is the vertical step size and `b` is the horizontal step size. When creating the layer, you can specify `Stride` as a scalar to use the same value for both dimensions.

If the stride dimensions `Stride` are less than the respective pooling dimensions, then the pooling regions overlap.

The padding dimensions `PaddingSize` must be less than the pooling region dimensions `PoolSize`.

Example: `[2 3]` specifies a vertical step size of 2 and a horizontal step size of 3.

Size of padding to apply to input borders, specified as a vector `[t b l r]` of four nonnegative integers, where `t` is the padding applied to the top, `b` is the padding applied to the bottom, `l` is the padding applied to the left, and `r` is the padding applied to the right.

When you create a layer, use the `'Padding'` name-value pair argument to specify the padding size.

Example: `[1 1 2 2]` adds one row of padding to the top and bottom, and two columns of padding to the left and right of the input.

Method to determine padding size, specified as `'manual'` or `'same'`.

The software automatically sets the value of `PaddingMode` based on the `'Padding'` value you specify when creating a layer.

• If you set the `'Padding'` option to a scalar or a vector of nonnegative integers, then the software automatically sets `PaddingMode` to `'manual'`.

• If you set the `'Padding'` option to `'same'`, then the software automatically sets `PaddingMode` to `'same'` and calculates the size of the padding at training time so that the output has the same size as the input when the stride equals 1. If the stride is larger than 1, then the output size is `ceil(inputSize/stride)`, where `inputSize` is the height or width of the input and `stride` is the stride in the corresponding dimension. The software adds the same amount of padding to the top and bottom, and to the left and right, if possible. If the padding that must be added vertically has an odd value, then the software adds extra padding to the bottom. If the padding that must be added horizontally has an odd value, then the software adds extra padding to the right.

Value used to pad input, specified as `0` or `"mean"`.

When you use the `Padding` option to add padding to the input, the value of the padding applied can be one of the following:

• `0` — Input is padded with zeros at the positions specified by the `Padding` property. The padded areas are included in the calculation of the average value of the pooling regions along the edges.

• `"mean"` — Input is padded with the mean of the pooling region at the positions specified by the `Padding` option. The padded areas are effectively excluded from the calculation of the average value of each pooling region.

Note

`Padding` property will be removed in a future release. Use `PaddingSize` instead. When creating a layer, use the `'Padding'` name-value pair argument to specify the padding size.

Size of padding to apply to input borders vertically and horizontally, specified as a vector `[a b]` of two nonnegative integers, where `a` is the padding applied to the top and bottom of the input data and `b` is the padding applied to the left and right.

Example: `[1 1]` adds one row of padding to the top and bottom, and one column of padding to the left and right of the input.

### Layer

Layer name, specified as a character vector or a string scalar. For `Layer` array input, the `trainNetwork`, `assembleNetwork`, `layerGraph`, and `dlnetwork` functions automatically assign names to layers with name `''`.

Data Types: `char` | `string`

Number of inputs of the layer. This layer accepts a single input only.

Data Types: `double`

Input names of the layer. This layer accepts a single input only.

Data Types: `cell`

Number of outputs of the layer. This layer has a single output only.

Data Types: `double`

Output names of the layer. This layer has a single output only.

Data Types: `cell`

## Examples

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Create an average pooling layer with the name `'avg1'`.

`layer = averagePooling2dLayer(2,'Name','avg1')`
```layer = AveragePooling2DLayer with properties: Name: 'avg1' Hyperparameters PoolSize: [2 2] Stride: [1 1] PaddingMode: 'manual' PaddingSize: [0 0 0 0] PaddingValue: 0 ```

Include an average pooling layer in a `Layer` array.

```layers = [ ... imageInputLayer([28 28 1]) convolution2dLayer(5,20) reluLayer averagePooling2dLayer(2) fullyConnectedLayer(10) softmaxLayer classificationLayer]```
```layers = 7x1 Layer array with layers: 1 '' Image Input 28x28x1 images with 'zerocenter' normalization 2 '' Convolution 20 5x5 convolutions with stride [1 1] and padding [0 0 0 0] 3 '' ReLU ReLU 4 '' Average Pooling 2x2 average pooling with stride [1 1] and padding [0 0 0 0] 5 '' Fully Connected 10 fully connected layer 6 '' Softmax softmax 7 '' Classification Output crossentropyex ```

Create an average pooling layer with nonoverlapping pooling regions.

`layer = averagePooling2dLayer(2,'Stride',2)`
```layer = AveragePooling2DLayer with properties: Name: '' Hyperparameters PoolSize: [2 2] Stride: [2 2] PaddingMode: 'manual' PaddingSize: [0 0 0 0] PaddingValue: 0 ```

The height and width of the rectangular regions (pool size) are both 2. The pooling regions do not overlap because the step size for traversing the images vertically and horizontally (stride) is also 2.

Include an average pooling layer with nonoverlapping regions in a `Layer` array.

```layers = [ ... imageInputLayer([28 28 1]) convolution2dLayer(5,20) reluLayer averagePooling2dLayer(2,'Stride',2) fullyConnectedLayer(10) softmaxLayer classificationLayer]```
```layers = 7x1 Layer array with layers: 1 '' Image Input 28x28x1 images with 'zerocenter' normalization 2 '' Convolution 20 5x5 convolutions with stride [1 1] and padding [0 0 0 0] 3 '' ReLU ReLU 4 '' Average Pooling 2x2 average pooling with stride [2 2] and padding [0 0 0 0] 5 '' Fully Connected 10 fully connected layer 6 '' Softmax softmax 7 '' Classification Output crossentropyex ```

Create an average pooling layer with overlapping pooling regions.

`layer = averagePooling2dLayer([3 2],'Stride',2)`
```layer = AveragePooling2DLayer with properties: Name: '' Hyperparameters PoolSize: [3 2] Stride: [2 2] PaddingMode: 'manual' PaddingSize: [0 0 0 0] PaddingValue: 0 ```

This layer creates pooling regions of size [3 2] and takes the average of the six elements in each region. The pooling regions overlap because `Stride` includes dimensions that are less than the respective pooling dimensions `PoolSize`.

Include an average pooling layer with overlapping pooling regions in a `Layer` array.

```layers = [ ... imageInputLayer([28 28 1]) convolution2dLayer(5,20) reluLayer averagePooling2dLayer([3 2],'Stride',2) fullyConnectedLayer(10) softmaxLayer classificationLayer]```
```layers = 7x1 Layer array with layers: 1 '' Image Input 28x28x1 images with 'zerocenter' normalization 2 '' Convolution 20 5x5 convolutions with stride [1 1] and padding [0 0 0 0] 3 '' ReLU ReLU 4 '' Average Pooling 3x2 average pooling with stride [2 2] and padding [0 0 0 0] 5 '' Fully Connected 10 fully connected layer 6 '' Softmax softmax 7 '' Classification Output crossentropyex ```