classify

Classify data using a trained deep learning neural network

You can make predictions using a trained neural network for deep learning on either a CPU or GPU. Using a GPU requires Parallel Computing Toolbox™ and a CUDA® enabled NVIDIA® GPU with compute capability 3.0 or higher. Specify the hardware requirements using the ExecutionEnvironment name-value pair argument.

Syntax

[YPred,scores] = classify(net,X)
[YPred,scores] = classify(net,sequences)
[YPred,scores] = classify(___,Name,Value)

Description

example

[YPred,scores] = classify(net,X) predicts class labels for the image data in X using the trained network, net.

example

[YPred,scores] = classify(net,sequences) predicts class labels for the time series or sequence data in sequences using the trained LSTM network, net.

example

[YPred,scores] = classify(___,Name,Value) predicts class labels with additional options specified by one or more name-value pair arguments.

Tip

When making predictions with sequences of different lengths, the mini-batch size can impact the amount of padding added to the input data which can result in different predicted values. Try using different values to see which works best with your network. To specify mini-batch size and padding options, use the 'MiniBatchSize' and 'SequenceLength' options.

Examples

collapse all

Load the sample data.

[XTrain,YTrain] = digitTrain4DArrayData;

digitTrain4DArrayData loads the digit training set as 4-D array data. XTrain is a 28-by-28-by-1-by-5000 array, where 28 is the height and 28 is the width of the images. 1 is the number of channels and 5000 is the number of synthetic images of handwritten digits. YTrain is a categorical vector containing the labels for each observation.

Construct the convolutional neural network architecture.

layers = [ ...
    imageInputLayer([28 28 1])
    convolution2dLayer(5,20)
    reluLayer
    maxPooling2dLayer(2,'Stride',2)
    fullyConnectedLayer(10)
    softmaxLayer
    classificationLayer];

Set the options to default settings for the stochastic gradient descent with momentum.

options = trainingOptions('sgdm');

Train the network.

rng('default')
net = trainNetwork(XTrain,YTrain,layers,options);
Training on single CPU.
Initializing input data normalization.
|========================================================================================|
|  Epoch  |  Iteration  |  Time Elapsed  |  Mini-batch  |  Mini-batch  |  Base Learning  |
|         |             |   (hh:mm:ss)   |   Accuracy   |     Loss     |      Rate       |
|========================================================================================|
|       1 |           1 |       00:00:00 |       11.72% |       2.2909 |          0.0100 |
|       2 |          50 |       00:00:04 |       52.34% |       1.8173 |          0.0100 |
|       3 |         100 |       00:00:09 |       66.41% |       1.1120 |          0.0100 |
|       4 |         150 |       00:00:13 |       67.19% |       0.9866 |          0.0100 |
|       6 |         200 |       00:00:17 |       73.44% |       0.7928 |          0.0100 |
|       7 |         250 |       00:00:23 |       81.25% |       0.6349 |          0.0100 |
|       8 |         300 |       00:00:29 |       83.59% |       0.6307 |          0.0100 |
|       9 |         350 |       00:00:36 |       83.59% |       0.4726 |          0.0100 |
|      11 |         400 |       00:00:42 |       92.97% |       0.3709 |          0.0100 |
|      12 |         450 |       00:00:47 |       95.31% |       0.2842 |          0.0100 |
|      13 |         500 |       00:00:51 |       92.19% |       0.2760 |          0.0100 |
|      15 |         550 |       00:00:54 |       98.44% |       0.2186 |          0.0100 |
|      16 |         600 |       00:00:58 |       96.88% |       0.2164 |          0.0100 |
|      17 |         650 |       00:01:02 |       96.88% |       0.1960 |          0.0100 |
|      18 |         700 |       00:01:06 |      100.00% |       0.1066 |          0.0100 |
|      20 |         750 |       00:01:10 |       99.22% |       0.0850 |          0.0100 |
|      21 |         800 |       00:01:14 |       99.22% |       0.1224 |          0.0100 |
|      22 |         850 |       00:01:18 |       99.22% |       0.0832 |          0.0100 |
|      24 |         900 |       00:01:22 |       97.66% |       0.1246 |          0.0100 |
|      25 |         950 |       00:01:26 |       98.44% |       0.0821 |          0.0100 |
|      26 |        1000 |       00:01:30 |       99.22% |       0.0601 |          0.0100 |
|      27 |        1050 |       00:01:36 |       99.22% |       0.0679 |          0.0100 |
|      29 |        1100 |       00:01:40 |       99.22% |       0.0519 |          0.0100 |
|      30 |        1150 |       00:01:44 |       99.22% |       0.0591 |          0.0100 |
|      30 |        1170 |       00:01:45 |      100.00% |       0.0579 |          0.0100 |
|========================================================================================|

Run the trained network on a test set.

[XTest,YTest]= digitTest4DArrayData;
YPred = classify(net,XTest);

Display the first 10 images in the test data and compare to the classification from classify.

[YTest(1:10,:) YPred(1:10,:)]
ans = 10x2 categorical array
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 
     0      0 

The results from classify match the true digits for the first ten images.

Calculate the accuracy over all test data.

accuracy = sum(YPred == YTest)/numel(YTest)
accuracy = 0.9794

Load pretrained network. JapaneseVowelsNet is a pretrained LSTM network trained on the Japanese Vowels dataset as described in [1] and [2]. It was trained on the sequences sorted by sequence length with a mini-batch size of 27.

load JapaneseVowelsNet

View the network architecture.

net.Layers
ans = 
  5x1 Layer array with layers:

     1   'sequenceinput'   Sequence Input          Sequence input with 12 dimensions
     2   'lstm'            LSTM                    LSTM with 100 hidden units
     3   'fc'              Fully Connected         9 fully connected layer
     4   'softmax'         Softmax                 softmax
     5   'classoutput'     Classification Output   crossentropyex with '1' and 8 other classes

Load the test data.

load JapaneseVowelsTest

Classify the test data.

YPred = classify(net,XTest);

View the labels of the first 10 sequences with their predicted labels.

[YTest(1:10) YPred(1:10)]
ans = 10x2 categorical array
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 
     1      1 

Calculate the classification accuracy of the predictions.

accuracy = sum(YPred == YTest)/numel(YTest)
accuracy = 0.8595

Input Arguments

collapse all

Trained network, specified as a SeriesNetwork or a DAGNetwork object. You can get a trained network by importing a pretrained network (for example, by using the alexnet function) or by training your own network using trainNetwork.

Image data, specified as one of the following.

InputDescription
3-D arrayNumeric array that represents a single image. The array has size h-by-w-by-c, where h, w, and c correspond to the height, width, and the number of channels of the image, respectively.
4-D arrayNumeric array that represents a stack of images. The array has size h-by-w-by-c-by-N, where N is the number of images in the image stack.
Image datastore

ImageDatastore with categorical labels.

For more information, see the imds argument of trainNetwork.

Datastore

Datastore that returns data as a single image, a cell array of images, or a table whose first column contains images.

For more information, see Datastores for Deep Learning.

Table

The first column of the table contains either image paths or 3-D arrays representing images. Subsequent columns contain the responses.

For more information, see the tbl argument of trainNetwork.

Sequence or time series data, specified as an N-by-1 cell array of numeric arrays, where N is the number of observations, a numeric array representing a single sequence, or a datastore.

For cell array or numeric array input, the dimensions of the numeric arrays containing the sequences depend on the type of data.

InputDescription
Vector sequencesc-by-s matrices, where c is the number of features of the sequences and s is the sequence length.
2-D image sequencesh-by-w-by-c-by-s arrays, where h, w, and c correspond to the height, width, and number of channels of the images, respectively, and s is the sequence length.
3-D image sequencesh-by-w-by-d-by-c-by-s, where h, w, d, and c correspond to the height, width, depth, and number of channels of the 3-D images, respectively, and s is the sequence length.

For datastore input, the datastore must return data as a cell array of sequences or a table whose first column contains sequences. The dimensions of the sequence data must correspond to the table above.

Name-Value Pair Arguments

Example: 'MiniBatchSize','256' specifies the mini-batch size as 256.

Specify optional comma-separated pair of Name,Value argument. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (' ').

Size of mini-batches to use for prediction, specified as a positive integer. Larger mini-batch sizes require more memory, but can lead to faster predictions.

When making predictions with sequences of different lengths, the mini-batch size can impact the amount of padding added to the input data which can result in different predicted values. Try using different values to see which works best with your network. To specify mini-batch size and padding options, use the 'MiniBatchSize' and 'SequenceLength' options.

Example: 'MiniBatchSize',256

Performance optimization, specified as the comma-separated pair consisting of 'Acceleration' and one of the following:

  • 'auto' — Automatically apply a number of optimizations suitable for the input network and hardware resource.

  • 'mex' — Compile and execute a MEX function. This option is available when using a GPU only. Using a GPU requires Parallel Computing Toolbox and a CUDA enabled NVIDIA GPU with compute capability 3.0 or higher. If Parallel Computing Toolbox or a suitable GPU is not available, then the software returns an error.

  • 'none' — Disable all acceleration.

The default option is 'auto'. If 'auto' is specified, MATLAB® will apply a number of compatible optimizations. If you use the 'auto' option, MATLAB does not ever generate a MEX function.

Using the 'Acceleration' options 'auto' and 'mex' can offer performance benefits, but at the expense of an increased initial run time. Subsequent calls with compatible parameters are faster. Use performance optimization when you plan to call the function multiple times using new input data.

The 'mex' option generates and executes a MEX function based on the network and parameters used in the function call. You can have several MEX functions associated with a single network at one time. Clearing the network variable also clears any MEX functions associated with that network.

The 'mex' option is only available for input data specified as a numeric array, cell array of numeric arrays, table, or image datastore. No other types of datastore support the 'mex' option.

The 'mex' option is only available when you are using a GPU. You must also have a C/C++ compiler installed. For setup instructions, see MEX Setup (GPU Coder).

'mex' acceleration does not support all layers. For a list of supported layers, see Supported Layers (GPU Coder).

Example: 'Acceleration','mex'

Hardware resource, specified as the comma-separated pair consisting of 'ExecutionEnvironment' and one of the following:

  • 'auto' — Use a GPU if one is available; otherwise, use the CPU.

  • 'gpu' — Use the GPU. Using a GPU requires Parallel Computing Toolbox and a CUDA enabled NVIDIA GPU with compute capability 3.0 or higher. If Parallel Computing Toolbox or a suitable GPU is not available, then the software returns an error.

  • 'cpu' — Use the CPU.

Example: 'ExecutionEnvironment','cpu'

Option to pad, truncate, or split input sequences, specified as one of the following:

  • 'longest' — Pad sequences in each mini-batch to have the same length as the longest sequence. This option does not discard any data, though padding can introduce noise to the network.

  • 'shortest' — Truncate sequences in each mini-batch to have the same length as the shortest sequence. This option ensures that no padding is added, at the cost of discarding data.

  • Positive integer — For each mini-batch, pad the sequences to the nearest multiple of the specified length that is greater than the longest sequence length in the mini-batch, and then split the sequences into smaller sequences of the specified length. If splitting occurs, then the software creates extra mini-batches. Use this option if the full sequences do not fit in memory. Alternatively, try reducing the number of sequences per mini-batch by setting the 'MiniBatchSize' option to a lower value.

If you specify the sequence length as a positive integer, then the software processes the smaller sequences in consecutive iterations. The network updates the network state between the split sequences.

The software pads and truncates the sequences on the right. To learn more about the effect of padding, truncating, and splitting the input sequences, see Sequence Padding, Truncation, and Splitting.

Example: 'SequenceLength','shortest'

Value by which to pad input sequences, specified as a scalar. The option is valid only when SequenceLength is 'longest' or a positive integer. Do not pad sequences with NaN, because doing so can propagate errors throughout the network.

Example: 'SequencePaddingValue',-1

Output Arguments

collapse all

Predicted class labels, returned as a categorical vector, or a cell array of categorical vectors. The format of YPred depends on the type of problem.

The following table describes the format for classification problems.

TaskFormat
Image classificationN-by-1 categorical vector of labels, where N is the number of observations.
Sequence-to-label classification
Sequence-to-sequence classification

N-by-1 cell array of categorical sequences of labels, where N is the number of observations. Each sequence has the same number of time steps as the corresponding input sequence.

For sequence-to-sequence classification problems with one observation, sequences can be a matrix. In this case, YPred is a categorical sequence of labels.

Predicted scores or responses, returned as a matrix or a cell array of matrices. The format of scores depends on the type of problem.

The following table describes the format of scores.

TaskFormat
Image classificationN-by-K matrix, where N is the number of observations, and K is the number of classes
Sequence-to-label classification
Sequence-to-sequence classification

N-by-1 cell array of matrices, where N is the number of observations. The sequences are matrices with K rows, where K is the number of responses. Each sequence has the same number of time steps as the corresponding input sequence.

For sequence-to-sequence classification problems with one observation, sequences can be a matrix. In this case, scores is a matrix of predicted class scores.

For an example exploring classification scores, see Classify Webcam Images Using Deep Learning.

Algorithms

All functions for deep learning training, prediction, and validation in Deep Learning Toolbox™ perform computations using single-precision, floating-point arithmetic. Functions for deep learning include trainNetwork, predict, classify, and activations. The software uses single-precision arithmetic when you train networks using both CPUs and GPUs.

Alternatives

You can compute the predicted scores from a trained network using predict.

You can also compute the activations from a network layer using activations.

For sequence-to-label and sequence-to-sequence classification networks, you can make predictions and update the network state using classifyAndUpdateState and predictAndUpdateState.

References

[1] M. Kudo, J. Toyama, and M. Shimbo. "Multidimensional Curve Classification Using Passing-Through Regions." Pattern Recognition Letters. Vol. 20, No. 11–13, pages 1103–1111.

[2] UCI Machine Learning Repository: Japanese Vowels Dataset. https://archive.ics.uci.edu/ml/datasets/Japanese+Vowels

Introduced in R2016a