checkLayer

Check validity of custom or function layer

Syntax

checkLayer(layer,layout1,...,layoutN)

checkLayer(layer,validInputSize)

checkLayer(___,Name=Value)

Description

checkLayer(layer,layout1,...,layoutN) checks the validity of a layer using the specified networkDataLayout objects, where N is the number of layer inputs and layoutK corresponds to the input layer.InputNames(K). (since R2023b)

checkLayer(layer,validInputSize) checks the validity of a custom or function layer using generated data of the sizes in validInputSize. For layers with a single input, set validInputSize to a typical size of input data to the layer. For layers with multiple inputs, set validInputSize to a cell array of typical sizes, where each element corresponds to a layer input. This syntax does not support layers that inherit from the nnet.layer.Formattable class.

checkLayer(___,Name=Value) specifies additional options using one or more name-value arguments.

Examples

Check Validity of Custom Flatten Layer

Create a function layer object that applies the flatten function to the layer input. The flatten function is defined at the end of this example and collapses the spatial dimensions of the input dlarray into the channel dimension.

customFlattenLayer = functionLayer(@(X) flatten(X),Formattable=true)

customFlattenLayer = 
  FunctionLayer with properties:

             Name: ''
       PredictFcn: @(X)flatten(X)
      Formattable: 1
    Acceleratable: 0

   Learnable Parameters
    No properties.

   State Parameters
    No properties.

Use properties method to see a list of all properties.

Specify the size and dimensions of the inputs to the layer using networkDataLayout objects.

layout = networkDataLayout([227 227 3 NaN],"SSCB")

layout = 
  networkDataLayout with properties:

      Size: [227 227 3 NaN]
    Format: 'SSCB'

Check that the layer is valid using the checkLayer function.

checkLayer(customFlattenLayer,layout)

Skipping initialization tests. The layer does not have an initialize function.
 
Skipping GPU tests. No compatible GPU device found.
 
Skipping code generation compatibility tests. To check validity of the layer for code generation, specify the CheckCodegenCompatibility and ObservationDimension options.
 
Running nnet.checklayer.TestLayerWithoutBackward
.......... ........
Done nnet.checklayer.TestLayerWithoutBackward
__________

Test Summary:
	 18 Passed, 0 Failed, 0 Incomplete, 16 Skipped.
	 Time elapsed: 0.44429 seconds.

In this case, the function does not detect any issues with the layer.

Flatten Function

The flatten function receives a formatted dlarray as input and collapses the spatial dimensions of the input dlarray into the channel dimension. The input dlarray must not contain time ("T") or unspecified ("U") dimensions.

function Y = flatten(X)
% Find spatial, channel, and batch dimensions.
idxS = finddim(X,"S");
idxC = finddim(X,"C");
idxB = finddim(X,"B");

% Determine size of spatial and channel dimensions.
sizeS = size(X,idxS);
sizeC = size(X,idxC);

if ~isempty(idxB)
    % If the input has a batch dimension, determine the size of the output
    % channel dimension.
    numChannels = sizeC*prod(sizeS,"all");
    sizeB = size(X,idxB);

    % Reshape and format output in "CB" format.
    X = reshape(X,[numChannels sizeB]);
    Y = dlarray(X,"CB");
else
    % If the input does not have a batch dimension, reshape and output in
    % "CU" format.
    X = X(:);
    Y = dlarray(X,"CU");
end

end

Check Custom Layer Validity

Check the validity of the example custom layer sreluLayer.

The custom layer sreluLayer, attached to this example as a supporting file, applies the SReLU operation to the input data. To access this layer, open this example as a live script.

Create an instance of the layer.

layer = sreluLayer;

Create a networkDataLayout object that specifies the expected input size and format of a single observation of typical input to the layer. Specify a valid input size of [24 24 20 128], where the dimensions correspond to the height, width, number of channels, and number of observations of the previous layer output. Specify the data has format "SSCB" (spatial, spatial, channel, batch).

validInputSize = [24 24 20 128];
layout = networkDataLayout(validInputSize,"SSCB");

Check the layer validity using checkLayer. When you pass data through the network, the layer expects 4-D array inputs, where the first three dimensions correspond to the height, width, and number of channels of the previous layer output, and the fourth dimension corresponds to the observations.

checkLayer(layer,layout)

Skipping GPU tests. No compatible GPU device found.
 
Skipping code generation compatibility tests. To check validity of the layer for code generation, specify the CheckCodegenCompatibility and ObservationDimension options.
 
Running nnet.checklayer.TestLayerWithoutBackward
.......... ..........
Done nnet.checklayer.TestLayerWithoutBackward
__________

Test Summary:
	 20 Passed, 0 Failed, 0 Incomplete, 14 Skipped.
	 Time elapsed: 0.1629 seconds.

The results show the number of passed, failed, and skipped tests. If you do not have a GPU, then the function skips the corresponding tests.

Check Function Layer Validity

Create a function layer object that applies the softsign operation to the input. The softsign operation is given by the function $\mathit{f}\left(\mathit{x}\right)=\frac{\mathit{x}}{1+\left|\mathit{x}\right|}$.

layer = functionLayer(@(X) X./(1 + abs(X)))

layer = 
  FunctionLayer with properties:

             Name: ''
       PredictFcn: @(X)X./(1+abs(X))
      Formattable: 0
    Acceleratable: 0

   Learnable Parameters
    No properties.

   State Parameters
    No properties.

Use properties method to see a list of all properties.

Check that the layer it is valid using the checkLayer function. Set the valid input size to the typical size of a single observation input to the layer. For example, for a single input, the layer expects observations of size h-by-w-by-c, where h, w, and c are the height, width, and number of channels of the previous layer output, respectively.

Specify validInputSize as the typical size of an input array.

validInputSize = [5 5 20];
checkLayer(layer,validInputSize)

Skipping initialization tests. The layer does not have an initialize function.
 
Skipping multi-observation tests. To enable tests with multiple observations, specify a formatted networkDataLayout as the second argument or specify the ObservationDimension option.
For 2-D image data, set ObservationDimension to 4.
For 3-D image data, set ObservationDimension to 5.
For sequence data, set ObservationDimension to 2.
 
Skipping GPU tests. No compatible GPU device found.
 
Skipping code generation compatibility tests. To check validity of the layer for code generation, specify the CheckCodegenCompatibility and ObservationDimension options.
 
Running nnet.checklayer.TestLayerWithoutBackward
.......... ..
Done nnet.checklayer.TestLayerWithoutBackward
__________

Test Summary:
	 12 Passed, 0 Failed, 0 Incomplete, 22 Skipped.
	 Time elapsed: 0.23257 seconds.

The results show the number of passed, failed, and skipped tests. If you do not specify the ObservationsDimension option, or do not have a GPU, then the function skips the corresponding tests.

Check Multiple Observations

For multi-observation image input, the layer expects an array of observations of size h-by-w-by-c-by-N, where h, w, and c are the height, width, and number of channels, respectively, and N is the number of observations.

To check the layer validity for multiple observations, specify the typical size of an observation and set the ObservationDimension option to 4.

layer = functionLayer(@(X) X./(1 + abs(X)));
validInputSize = [5 5 20];
checkLayer(layer,validInputSize,ObservationDimension=4)

Skipping initialization tests. The layer does not have an initialize function.
 
Skipping GPU tests. No compatible GPU device found.
 
Skipping code generation compatibility tests. To check validity of the layer for code generation, specify the CheckCodegenCompatibility and ObservationDimension options.
 
Running nnet.checklayer.TestLayerWithoutBackward
.......... ........
Done nnet.checklayer.TestLayerWithoutBackward
__________

Test Summary:
	 18 Passed, 0 Failed, 0 Incomplete, 16 Skipped.
	 Time elapsed: 0.14452 seconds.

In this case, the function does not detect any issues with the layer.

Check Custom Layer for Code Generation Compatibility

Check the code generation compatibility of the custom layer codegenSReLULayer.

The custom layer codegenSReLULayer, attached to this is example as a supporting file, applies the SReLU operation to the input data. To access this layer, open this example as a live script.

Create an instance of the layer.

layer = codegenSReLULayer;

Create a networkDataLayout object that specifies the expected input size and format of typical input to the layer. Specify a valid input size of [24 24 20 128], where the dimensions correspond to the height, width, number of channels, and number of observations of the previous layer output. Specify the format as "SSCB" (spatial, spatial, channel, batch).

validInputSize = [24 24 20 128];
layout = networkDataLayout(validInputSize,"SSCB");

Check the layer validity using checkLayer. To check for code generation compatibility, set the CheckCodegenCompatibility option to true. The checkLayer function does not check that the layer uses MATLAB functions that are compatible with code generation. To check that the custom layer definition is supported for code generation, first use the Code Generation Readiness app. For more information, see Check Code by Using the Code Generation Readiness Tool (MATLAB Coder).

checkLayer(layer,layout,CheckCodegenCompatibility=true)

Skipping GPU tests. No compatible GPU device found.
 
Running nnet.checklayer.TestLayerWithoutBackward
.......... .......... .....
Done nnet.checklayer.TestLayerWithoutBackward
__________

Test Summary:
	 25 Passed, 0 Failed, 0 Incomplete, 9 Skipped.
	 Time elapsed: 1.1221 seconds.

The function does not detect any issues with the layer.

Input Arguments

layer — Layer to check

nnet.layer.Layer object | FunctionLayer

Layer to check, specified as an nnet.layer.Layer or FunctionLayer object.

If the layer has learnable or state parameters which require initialization before layer can be evaluated, or if the layer has a custom initialize function, then you must specify a layout or the layer must be initialized.

For an example showing how to define your own custom layer, see Define Custom Deep Learning Layer with Learnable Parameters. To create a layer that applies a specified function, use functionLayer.

layout1,...,layoutN — Network data layouts

networkDataLayout object

Since R2023b

Valid network data layouts for each input to the layer, specified as networkDataLayout objects.

• For layers with a single input, specify a single layout.

• For layers with multiple inputs, specify a layout for each input. For example, for a layer with two inputs, specify layout1,layout2, where layout1 corresponds to the valid network data layout for the first input and layout2 corresponds to the valid network data layout for the second input.

If the layer inherits from the nnet.layer.Formattable class, you must specify a networkDataLayout for each input to the layer.

For large input sizes, the gradient checks take longer to run. To speed up the check, specify a network data layout with a smaller size using the Size property.

validInputSize — Valid input sizes

vector of positive integers | cell array of vectors of positive integers

Valid input sizes of the layer, specified as a vector of positive integers or cell array of vectors of positive integers.

• For layers with a single input, specify validInputSize as a vector of integers corresponding to the dimensions of the input data. For example, [5 5 10] corresponds to valid input data of size 5-by-5-by-10.

• For layers with multiple inputs, specify validInputSize as a cell array of vectors, where each vector corresponds to a layer input and the elements of the vectors correspond to the dimensions of the corresponding input data. For example, {[24 24 20],[24 24 10]} corresponds to the valid input sizes of two inputs, where 24-by-24-by-20 is a valid input size for the first input and 24-by-24-by-10 is a valid input size for the second input.

For more information, see Layer Input Sizes.

For large input sizes, the gradient checks take longer to run. To speed up the check, specify a smaller valid input size.

Example: [5 5 10]

Example: {[24 24 20],[24 24 10]}

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

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: ObservationDimension=4 sets the observation dimension to 4

ObservationDimension — Observation dimension

positive integer | row vector of positive integers

Observation dimension, specified as a positive integer or row vector of positive integers. The default is the position of the batch ("B") dimensions of the network data layouts layout1,...,layoutN.

The observation dimension specifies which dimension of the layer input data corresponds to observations. For example, if the layer expects input data is of size h-by-w-by-c-by-N, where h, w, and c correspond to the height, width, and number of channels of the input data, respectively, and N corresponds to the number of observations, then the observation dimension is 4. For more information, see Layer Input Sizes.

If you specify a network data layout with a batch dimension or if you specify the observation dimension, then the checkLayer function checks that the layer functions are valid using generated data with mini-batches of size 1 and 2. Otherwise, the function skips the corresponding tests.

Example: 4

Example: [4 4 2]

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

CheckCodegenCompatibility — Flag to enable code generation tests

0 (false) (default) | 1 (true)

Flag to enable code generation tests, specified as 0 (false) or 1 (true).

If CheckCodegenCompatibility is 1 (true), then you must specify a layout whose Format property includes a batch ("B") dimension or specify the ObservationDimension option.

The CheckCodegenCompatibility option does not support layers that inherit from nnet.layer.Formattable. Instead, use the analyzeNetworkForCodegen (MATLAB Coder) function.

In addition, when generating code that uses third-party libraries:

• Code generation supports custom layers with 2-D image or feature input only.

• The inputs and output of the layer forward functions must have the same batch size.

• Nonscalar properties must be a single, double, or character array.

• Scalar properties must have type numeric, logical, or string.

The checkLayer function does not check that functions used by the layer are compatible with code generation. To check that functions used by the custom layer also support code generation, first use the Code Generation Readiness app. For more information, see Check Code by Using the Code Generation Readiness Tool (MATLAB Coder).

For an example showing how to define a custom layer that supports code generation, see Define Custom Deep Learning Layer for Code Generation.

Data Types: logical

More About

Layer Input Sizes

For each layer, the valid network data layout depends on the output of the previous layer.

Layer Input	Example
	Shape	Data Format
2-D images	h-by-w-by-c-by-N numeric array, where h, w, c and N are the height, width, number of channels of the images, and number of observations, respectively.	"SSCB"
3-D images	h-by-w-by-d-by-c-by-N numeric array, where h, w, d, c and N are the height, width, depth, number of channels of the images, and number of image observations, respectively.	"SSSCB"
Vector sequences	c-by-N-by-s matrix, where c is the number of features of the sequence, N is the number of sequence observations, and s is the sequence length.	"CBT"
2-D image sequences	h-by-w-by-c-by-N-by-s array, where h, w, and c correspond to the height, width, and number of channels of the image, respectively, N is the number of image sequence observations, and s is the sequence length.	"SSCBT"
3-D image sequences	h-by-w-by-d-by-c-by-N-by-s array, where h, w, d, and c correspond to the height, width, depth, and number of channels of the image, respectively, N is the number of image sequence observations, and s is the sequence length.	"SSSCBT"
Features	c-by-N array, where c is the number of features, and N is the number of observations.	"CB"

For example, for 2-D image classification problems, create a networkDataLayout object specifying the size as [h w c n] and the format as "SSCB", where h, w, and c correspond to the height, width, and number of channels of the images, respectively, and n corresponds to the number of observations.

Code generation supports layers with 2-D image input only.

Algorithms

List of Tests

The checkLayer function uses these tests to check the validity of custom layers.

Test	Description
functionSyntaxesAreCorrect	The syntaxes of the layer functions are correctly defined.
predictDoesNotError	predict function does not error.
forwardDoesNotError	When specified, the forward function does not error.
forwardPredictAreConsistentInSize	When forward is specified, forward and predict output values of the same size.
backwardDoesNotError	When specified, backward does not error.
backwardIsConsistentInSize	When backward is specified, the outputs of backward are consistent in size: The derivatives with respect to each input are the same size as the corresponding input. The derivatives with respect to each learnable parameter are the same size as the corresponding learnable parameter.
predictIsConsistentInType	The outputs of predict are consistent in type with the inputs.
forwardIsConsistentInType	When forward is specified, the outputs of forward are consistent in type with the inputs.
backwardIsConsistentInType	When backward is specified, the outputs of backward are consistent in type with the inputs.
gradientsAreNumericallyCorrect	When backward is specified, the gradients computed in backward are consistent with the numerical gradients.
backwardPropagationDoesNotError	When backward is not specified, the derivatives can be computed using automatic differentiation.
predictReturnsValidStates	For layers with state properties, the predict function returns valid states.
forwardReturnsValidStates	For layers with state properties, the forward function, if specified, returns valid states.
resetStateDoesNotError	For layers with state properties, the resetState function, if specified, does not error and resets the states to valid states.
formattableLayerPredictIsFormatted (since R2023b)	For layers that inherit from the nnet.layer.Formattable class, the predict function returns a formatted dlarray with a channel dimension.
formattableLayerForwardIsFormatted (since R2023b)	For layers that inherit from the nnet.layer.Formattable class, the forward function, if specified, returns a formatted dlarray with a channel dimension.
initializeDoesNotChangeLearnableParametersWhenTheyAreNotEmpty (since R2023b)	When you specify one or more networkDataLayout objects, the learnable parameters of the layer do not change after repeated initialization with the same networkDataLayout objects as input.
initializeDoesNotChangeStatefulParametersWhenTheyAreNotEmpty (since R2023b)	When you specify one or more networkDataLayout objects, the state parameters of the layer do not change after repeated initialization with the same networkDataLayout objects as input.
codegenPragmaDefinedInClassDef	The pragma "%#codegen" for code generation is specified in class file.
layerPropertiesSupportCodegen	The layer properties support code generation.
predictSupportsCodegen	predict is valid for code generation.
doesNotHaveStateProperties	For code generation, the layer does not have state properties.
functionLayerSupportsCodegen	For code generation, the layer function must be a named function on the path and the Formattable property must be 0 (false).

Some tests run multiple times. These tests also check different data types and for GPU compatibility:

• predictIsConsistentInType

• forwardIsConsistentInType

• backwardIsConsistentInType

To execute the layer functions on a GPU, the functions must support inputs and outputs of type gpuArray with the underlying data type single.

For more information on the tests used by checkLayer, see Check Custom Layer Validity.

Version History

Introduced in R2018a

R2024a: Custom output layers are not recommended

Custom output layers are not recommended. Use a custom loss function in the trainnet function instead.

This recommendation means that these syntaxes are not recommended for custom output layer input:

• checkLayer(layer,layout1,...,layoutN)

• checkLayer(layer,validInputSize)

• checkLayer(___,Name=Value)

There are no plans to remove support for custom output layers. However, the trainnet function has these advantages and is recommended instead:

• trainnet supports dlnetwork objects, which support a wider range of network architectures that you can create or import from external platforms.

• trainnet enables you to easily specify loss functions. You can select from built-in loss functions or specify a custom loss function.

• trainnet outputs a dlnetwork object, which is a unified data type that supports network building, prediction, built-in training, visualization, compression, verification, and custom training loops.

• trainnet is typically faster than trainNetwork.

This table shows some typical usages of the trainNetwork function with custom output layers and how to update your code to use the trainnet function instead.

Not Recommended	Recommended
net = trainNetwork(X,T,layers,options), where layers contains a custom output layer.	net = trainnet(X,T,layers,lossFcn,options); In this example, layers specifies same network without the custom output layer and lossFcn is a function handle the specifies the custom loss function.
net = trainNetwork(data,layers,options), where layers contains a custom output layer.	net = trainnet(data,layers,lossFcn,options); In this example, layers specifies same network without the custom output layer and lossFcn is a function handle the specifies the custom loss function.

R2023b: Check formattable custom layers and check custom layers without initializing

You can now use the checkLayer function to check the validity of custom layers that inherit from the nnet.layer.Formattable class by specifying a networkDataLayoutObject as the second argument.

You can also check the validity of a custom layer with a custom initialize function without first initializing the layer by using the checkLayer function and specifying a networkDataLayout as the second argument.