networkLayer

Network Layer

Since R2024a

Description

A network layer contains a nested network. Use network layers to simplify building large networks that contain repeating components.

During training and inference a network layer behaves identically to the nested network.

Tip

To visualize a network layer, use Deep Network Designer. To see inside the layer, double click the layer. To edit the layers in Deep Network Designer, you must first expand the network using the expandLayers function before opening the network in the app. After editing the network and exporting it to the workspace, you can regroup the layers into network layers using the groupLayers function. Adding a network layer to a network in Deep Network Designer is not supported.

Creation

Syntax

layer = networkLayer(net)

layer = networkLayer(___,Name=Value)

Description

layer = networkLayer(net) creates a network layer containing the neural network net.

layer = networkLayer(___,Name=Value) sets writable properties using on or more name-value arguments. For example, Name="myNetworkLayer" sets the name of the network layer.

Input Arguments

net — Neural Network

dlnetwork object | layer array

Neural network, specified as a dlnetwork object or a layer array.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: layer = networkLayer(net,Name="myNetworkLayer")

Name — Layer Name

"subnet" (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 layers with the name "".

This argument sets the Name property as a character vector.

Data Types: char | string

OutputNames — Names of layer outputs

cell array of character vectors

Names of the layer outputs, specified as a cell array of character vectors.

If you do not specify the output names, then the output names are the same as those of the nested network.

For layers with a single output, the output name is the name of the layer. For layers with multiple outputs, the output name is "layerName/outputName", where layerName is the name of the layer and outputName is the name of the layer output.

The predict and forward functions, by default, return the data output by the layers given by the OutputNames property.

This argument sets the OutputNames property.

Data Types: cell

Properties

Network — Nested network

Read-only: dlnetwork object

This property is read-only.

Nested network, specified as a dlnetwork object.

Name — Layer name

"subnet" (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 layers with the name "".

The NetworkLayer object stores this property as a character vector.

Data Types: char | string

InputNames — Names of layer inputs

Read-only: cell array of character vectors

This property is read-only.

Names of the layer inputs, specified as a cell array of character vectors.

Layer inputs are the unconnected inputs of the layers in the nested network.

For layers with a single input, the input name is the name of the layer. For layers with multiple inputs, the input name is "layerName/inputName", where layerName is the name of the layer and inputName is the name of the layer input.

Data Types: cell

OutputNames — Names of layer outputs

cell array of character vectors

Names of the layer outputs, specified as a cell array of character vectors.

If you do not specify the output names, then the output names are the same as those of the nested network.

For layers with a single output, the output name is the name of the layer. For layers with multiple outputs, the output name is "layerName/outputName", where layerName is the name of the layer and outputName is the name of the layer output.

The predict and forward functions, by default, return the data output by the layers given by the OutputNames property.

Data Types: cell

Examples

Create Network Layer

Create an array of layers containing an lstmLayer with 100 hidden units and a dropoutLayer with a dropout probability of 0.2.

layers = [lstmLayer(100,OutputMode="sequence")
    dropoutLayer(0.2)];

Create a network layer containing these layers.

lstmDropoutLayer = networkLayer(layers)

lstmDropoutLayer = 
  NetworkLayer with properties:

           Name: ''
     InputNames: {'lstm'}
    OutputNames: {'dropout'}

   Learnable Parameters
        Network: [1×1 dlnetwork]

   State Parameters
        Network: [1×1 dlnetwork]

  Show all properties

Inspect the layers of the network layer. This is equivalent to calling lstmDropoutLayer.Network.Layers.

lstmDropoutLayer.Layers

ans = 
  2×1 Layer array with layers:

     1   'lstm'      LSTM      LSTM with 100 hidden units
     2   'dropout'   Dropout   20% dropout

Use the network layer to build a network which you can train using the trainnet function.

layers = [sequenceInputLayer(3)
    lstmDropoutLayer
    lstmDropoutLayer
    fullyConnectedLayer(10)
    softmaxLayer];

Create Image Feature Extractor Layer

Download a pretrained image classification network.

resnet = imagePretrainedNetwork("resnet50");

Load a test image.

img = imread("peppers.png");
figure
imshow(img)

Use the pretrained network to create a network layer by specifying intermediate layers as the outputs of the network layer. This network layer can be used as a feature extractor, for example as the backbone of an object detection network such as a Mask R-CNN object detector.

extractorLayer = networkLayer(resnet,OutputNames=["activation_10_relu" "activation_22_relu" "activation_40_relu" "activation_49_relu"]);

Create a dlnetwork object containing the feature extractor and initialize the network using the test image.

img = dlarray(single(img),"SSC");
net = dlnetwork(extractorLayer,img);

Use the predict function to compute the outputs of network.

[output1,output2,output3,output4] = predict(net,img);
extractedFeatures = {output1 output2 output3 output4};

Average the extracted features over the channel dimension and plot the extracted features.

figure
t = tiledlayout("flow");
title(t,"Feature Maps")
for idx=1:numel(extractedFeatures)
    features = mean(extractdata(extractedFeatures{idx}),3);
    resolution = size(features);
    nexttile
    imagesc(features)
    title("Resolution: " + resolution(1) + "-by-" + resolution(2))
    axis off
end

Visualize Network Layer

Create an array of layers.

convLayers = [ ...
    convolution1dLayer(5,16,Padding="causal")
    reluLayer
    layerNormalizationLayer];

Use networkLayer to create a convolutional block of layers.

convBlock = networkLayer(convLayers);

Define a network containing two convolutional blocks.

layers = [ ...
    sequenceInputLayer(10)
    convBlock
    convBlock
    globalAveragePooling1dLayer
    fullyConnectedLayer(3)
    softmaxLayer];

Visualize the network using the Deep Network Designer app.

deepNetworkDesigner(layers)

To see inside the network layer, double click the layer.

To navigate up in the hierarchy, in the bar that appears above the canvas, click the name of the network whose level you want to see.

To edit the layers in Deep Network Designer, you must first expand the network using the expandLayers function before opening the network in the app. After editing the network and exporting it to the workspace, you can regroup the layers into network layers using the groupLayers function. Adding a network layer to a network in Deep Network Designer is not supported.

More About

Code Generation

To generate code for a trained network containing network layers, first expand the network using the expandLayers function.

Version History

Introduced in R2024a