deepSignalAnomalyDetectorLSTMForecaster

Detect signal anomalies using LSTM forecaster

Since R2024a

Description

The deepSignalAnomalyDetectorLSTMForecaster object uses a long short-term memory (LSTM) forecaster model to detect signal anomalies.

Creation

Create a deepSignalAnomalyDetectorLSTMForecaster object using deepSignalAnomalyDetector and specifying "lstmforecaster" as the model type.

Properties

General

IsTrained — Training status

0 (false) | 1 (true)

This property is read-only.

Training status, returned as 0 (false) or 1 (true). Once you train the detector, IsTrained is equal to 1.

Data Types: logical

NumChannels — Number of channels

positive integer

This property is read-only.

Number of channels in each input signal, returned as a positive integer.

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

Model

ModelType — Type of deep learning model

"lstmforecaster"

This property is read-only.

Type of deep learning model implemented by the detector, returned as "lstmforecaster".

ForecastSteps — Number of steps forward for forecasting

1 (default) | positive integer scalar

This property is read-only.

Number of steps forward for forecasting, returned as a positive integer scalar.

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

NumHiddenUnits — Number of hidden units of LSTM layers

16 (default) | positive integer scalar | vector of positive integers

This property is read-only.

Number of hidden units of LSTM layers, returned as a positive integer scalar or a vector of positive integers. The ith element of the vector sets the number of hidden units in the ith layer.

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

Window

WindowLength — Window length

1 (default) | positive integer | "fullSignal"

This property is read-only.

Window length of each signal segment, returned as a positive integer or as "fullSignal".

• If WindowLength is an integer, the detector divides each input signal into segments. The length of each segment is equal to the WindowLength value in samples.

• If WindowLength is "fullSignal", the detector treats each input signal as a single segment.

Use updateDetector to modify this and other window properties.

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

OverlapLength — Number of overlapped samples

"auto" (default) | positive integer

This property is read-only.

Number of overlapped samples between window segments, returned as a positive integer or as "auto".

• If OverlapLength is a positive integer, the detector sets the number of overlapped samples equal to the OverlapLength value.

• If OverlapLength is "auto", the detector sets the number of overlapped samples equal to WindowLength – 1.

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

WindowLossAggregation — Method to aggregate sample loss

"mean" (default) | "max" | "min" | "median"

This property is read-only.

Method to aggregate sample loss within each window segment, returned as one of these:

• "max" — Compute the aggregated window loss as the maximum value of all the sample losses within the window.

• "mean" — Compute the aggregated window loss as the mean value of all the sample losses within the window.

• "median" — Compute the aggregated window loss as the median value of all the sample losses within the window.

• "min" — Compute the aggregated window loss as the minimum value of all the sample losses within the window.

Data Types: char | string

Threshold

ThresholdMethod — Method to compute detection threshold

"contaminationFraction" (default) | "max" | "median" | "mean" | "manual" | "customFunction"

This property is read-only.

Method to compute the detection threshold, returned as one of these:

• "contaminationFraction" — Value corresponding to the detection of anomalies within a specified fraction of windows. The fraction value is specified by ThresholdParameter.

• "max" — Maximum window loss measured over the entire training data set and multiplied by ThresholdParameter.

• "median" — Median window loss measured over the entire training data set and multiplied by ThresholdParameter.

• "mean" — Mean window loss measured over the entire training data set and multiplied by ThresholdParameter.

• "manual" — Manual detection threshold value based on Threshold.

• "customFunction" — Custom detection threshold value based on ThresholdFunction.

Use updateDetector to modify this and other threshold properties.

Data Types: char | string

ThresholdParameter — Detection threshold

real scalar

This property is read-only.

Detection threshold, returned as a nonnegative scalar when you set ThresholdMethod to "contaminationFraction", and as positive scalar when you set ThresholdMethod to "max", "median", or "mean".

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

Threshold — Manual detection threshold

positive scalar

This property is read-only.

Manual detection threshold, returned as a positive scalar. This property applies only when you set ThresholdMethod to "manual".

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

ThresholdFunction — Function to compute custom detection threshold

function handle

This property is read-only.

Function to compute custom detection threshold, returned as a function handle. This property applies only when you set ThresholdMethod to "customFunction".

Data Types: function_handle

Object Functions

detect	Detect anomalies in signals
getModel	Get underlying neural network model of signal anomaly detector
plotAnomalies	Plot signal anomalies
plotLoss	Plot window reconstruction loss
plotLossDistribution	Plot CDF and histogram of aggregated window loss distribution
resetState	Reset model internal states
saveModel	Save detector network and parameters
trainDetector	Train signal anomaly detector
updateDetector	Update settings of trained detector and recompute detection threshold

Examples

Detect Anomalies in Streaming Sinusoids

Load the file sineWaveAnomalyData.mat, which contains two sets of synthetic three-channel sinusoidal signals.

• sineWaveNormal contains the 10 sinusoids used to train the convolutional anomaly detector. Each signal has a series of small-amplitude impact-like imperfections but otherwise has stable amplitude and frequency.

• sineWaveAbnormal contains three signals of similar length and amplitude to the training data. One of the signals has an abrupt, finite-time change in frequency. Another signal has a finite-duration amplitude change in one of its channels. A third has random spikes in each channel.

Plot three normal signals and the three signals with anomalies.

load sineWaveAnomalyData
 
tiledlayout(3,2,TileSpacing="compact",Padding="compact")
rnd = randperm(length(sineWaveNormal));
for kj = 1:length(sineWaveAbnormal)
    nexttile
    plot(sineWaveNormal{rnd(kj)})
    title("Normal Signal")
    nexttile
    plot(sineWaveAbnormal{kj})
    title("Signal with Anomalies")
end

Create a long short-term memory (LSTM) forecaster object to detect the anomalies in the abnormal signals. Specify a window length of 10 samples.

D = deepSignalAnomalyDetector(3,"lstmforecaster",windowLength=10);

Train the forecaster using the anomaly-free sinusoids. Use the training options for the adaptive moment estimation (Adam) optimizer and specify a maximum number of 100 epochs. For more information, see trainingOptions (Deep Learning Toolbox).

opts = trainingOptions("adam",MaxEpochs=100,ExecutionEnvironment="cpu");
trainDetector(D,sineWaveNormal,opts)

    Iteration    Epoch    TimeElapsed    LearnRate    TrainingLoss
    _________    _____    ___________    _________    ____________
            1        1       00:00:01        0.001          0.6369
           50       50       00:00:05        0.001         0.19706
          100      100       00:00:08        0.001        0.064225
Training stopped: Max epochs completed
Computing threshold...
Threshold computation completed.

Use the trained detector to find the anomalies in the first signal. Reset the state of the detector. Stream the data one sample at a time and have the detector keep its state after each reading. Compute the reconstruction loss for each one-sample frame. Categorize signal regions where the loss exceeds a specified threshold as anomalous.

resetState(D)

sg = sineWaveAbnormal{1};
anoms = NaN(size(sg));
losss = zeros(size(sg));

for kj = 1:length(sg)
    frame = sg(kj,:);
    [lb,lo] = detect(D,frame, ...
        KeepState=true,ExecutionEnvironment="cpu");
    anoms(kj) = lb;
    losss(kj) = lo;
end

Plot the anomalous signal, the reconstruction loss, and the categorical array that declares each sample of the signal as being anomalous or not.

figure
tiledlayout("vertical")
nexttile
plot(sg)
nexttile
plot(losss)
nexttile
stem(anoms,".")

Reset the state of the detector. Find the anomalies in the third signal. Plot the anomalous signal, the reconstruction loss, and the categorical array that declares each sample of the signal as being anomalous or not.

resetState(D)

sg = sineWaveAbnormal{3};
anoms = NaN(size(sg));
losss = zeros(size(sg));

for kj = 1:length(sg)
    frame = sg(kj,:);
    [lb,lo] = detect(D,frame, ...
        KeepState=true,ExecutionEnvironment="cpu");
    anoms(kj) = lb;
    losss(kj) = lo;
end

figure
tiledlayout("vertical")
nexttile
plot(sg)
nexttile
plot(losss)
nexttile
stem(anoms,".")

Extended Capabilities

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The deepSignalAnomalyDetectorLSTMForecaster function supports GPU array input with these usage notes and limitations:

• The ExecutionEnvironment option must be "gpu" or "auto" when the input data is:

  • A gpuArray

  • A cell array containing gpuArray objects

  • A datastore that outputs cell arrays containing gpuArray objects

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced in R2024a