sequenceUnfoldingLayer

Sequence unfolding layer

Since R2019a

Description

A sequence unfolding layer restores the sequence structure of the input data after sequence folding.

To use a sequence unfolding layer, you must connect the miniBatchSize output of the corresponding sequence folding layer to the miniBatchSize input of the sequence unfolding layer. For an example, see Create Network for Video Classification.

Creation

Syntax

layer = sequenceUnfoldingLayer

layer = sequenceUnfoldingLayer('Name',Name)

Description

layer = sequenceUnfoldingLayer creates a sequence unfolding layer.

layer = sequenceUnfoldingLayer('Name',Name) creates a sequence unfolding layer and sets the optional Name property using a name-value pair. For example, sequenceUnfoldingLayer('Name','unfold1') creates a sequence unfolding layer with the name 'unfold1'. Enclose the property name in single quotes.

Properties

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, trainNetwork, assembleNetwork, layerGraph, and dlnetwork functions automatically assign names to layers with the name "".

The SequenceUnfoldingLayer object stores this property as a character vector.

Data Types: char | string

NumInputs — Number of inputs

2 (default)

Number of inputs of the layer.

This layer has two inputs:

• 'in' – Input feature map.

• 'miniBatchSize' – Size of the mini-batch from the corresponding sequence folding layer. This output must be connected to the 'miniBatchSize' output of the corresponding sequence folding layer.

Data Types: double

InputNames — Input names

{'in','miniBatchSize'} (default)

Input names of the layer.

This layer has two inputs:

• 'in' – Input feature map.

• 'miniBatchSize' – Size of the mini-batch from the corresponding sequence folding layer. This output must be connected to the 'miniBatchSize' output of the corresponding sequence folding layer.

Data Types: cell

NumOutputs — Number of outputs

1 (default)

This property is read-only.

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

Data Types: double

OutputNames — Output names

{'out'} (default)

This property is read-only.

Output names, returned as {'out'}. This layer has a single output only.

Data Types: cell

Examples

Create Sequence Unfolding Layer

Create a sequence unfolding layer with the name 'unfold1'.

layer = sequenceUnfoldingLayer('Name','unfold1')

layer = 
  SequenceUnfoldingLayer with properties:

          Name: 'unfold1'
     NumInputs: 2
    InputNames: {'in'  'miniBatchSize'}

Create Network for Video Classification

Create a deep learning network for data containing sequences of images, such as video and medical image data.

• To input sequences of images into a network, use a sequence input layer.

• To apply convolutional operations independently to each time step, first convert the sequences of images to an array of images using a sequence folding layer.

• To restore the sequence structure after performing these operations, convert this array of images back to image sequences using a sequence unfolding layer.

• To convert images to feature vectors, use a flatten layer.

You can then input vector sequences into LSTM and BiLSTM layers.

Define Network Architecture

Create a classification LSTM network that classifies sequences of 28-by-28 grayscale images into 10 classes.

Define the following network architecture:

• A sequence input layer with an input size of [28 28 1].

• A convolution, batch normalization, and ReLU layer block with 20 5-by-5 filters.

• An LSTM layer with 200 hidden units that outputs the last time step only.

• A fully connected layer of size 10 (the number of classes) followed by a softmax layer and a classification layer.

To perform the convolutional operations on each time step independently, include a sequence folding layer before the convolutional layers. LSTM layers expect vector sequence input. To restore the sequence structure and reshape the output of the convolutional layers to sequences of feature vectors, insert a sequence unfolding layer and a flatten layer between the convolutional layers and the LSTM layer.

inputSize = [28 28 1];
filterSize = 5;
numFilters = 20;
numHiddenUnits = 200;
numClasses = 10;

layers = [ ...
    sequenceInputLayer(inputSize,'Name','input')
    
    sequenceFoldingLayer('Name','fold')
    
    convolution2dLayer(filterSize,numFilters,'Name','conv')
    batchNormalizationLayer('Name','bn')
    reluLayer('Name','relu')
    
    sequenceUnfoldingLayer('Name','unfold')
    flattenLayer('Name','flatten')
    
    lstmLayer(numHiddenUnits,'OutputMode','last','Name','lstm')
    
    fullyConnectedLayer(numClasses, 'Name','fc')
    softmaxLayer('Name','softmax')
    classificationLayer('Name','classification')];

Convert the layers to a layer graph and connect the miniBatchSize output of the sequence folding layer to the corresponding input of the sequence unfolding layer.

lgraph = layerGraph(layers);
lgraph = connectLayers(lgraph,'fold/miniBatchSize','unfold/miniBatchSize');

View the final network architecture using the plot function.

figure
plot(lgraph)

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 R2019a