sigmoidLayer

Sigmoid layer

Since R2020b

Description

A sigmoid layer applies a sigmoid function to the input such that the output is bounded in the interval (0,1).

Tip

To use the sigmoid layer for binary or multilabel classification problems, set the loss function argument of the trainnet to "binary-crossentropy".

Creation

Syntax

layer = sigmoidLayer

layer = sigmoidLayer('Name',Name)

Description

layer = sigmoidLayer creates a sigmoid layer.

layer = sigmoidLayer('Name',Name) creates a sigmoid layer and sets the optional Name property using a name-value pair argument. For example, sigmoidLayer('Name','sig1') creates a sigmoid layer with the name 'sig1'. 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 and dlnetwork functions automatically assign names to layers with the name "".

The SigmoidLayer object stores this property as a character vector.

Data Types: char | string

NumInputs — Number of inputs

1 (default)

This property is read-only.

Number of inputs to the layer, returned as 1. This layer accepts a single input only.

Data Types: double

InputNames — Input names

{'in'} (default)

This property is read-only.

Input names, returned as {'in'}. This layer accepts a single input only.

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 Sigmoid Layer

Create a sigmoid layer with the name 'sig1'.

layer = sigmoidLayer('Name', 'sig1')

layer = 
  SigmoidLayer with properties:

    Name: 'sig1'

   Learnable Parameters
    No properties.

   State Parameters
    No properties.

Use properties method to see a list of all properties.

Algorithms

Sigmoid Layer

A sigmoid layer applies a sigmoid function to the input such that the output is bounded in the interval (0,1).

This operation is equivalent to

$$f(x)=\frac{1}{1+e^{-x}}.$$

A multilabel classification problem can be thought of as a binary classification problem, where each class is considered independently of other classes as either present or not present. Solving this type of problem requires the sigmoid activation function, where for any sample x_n the posterior probability of class C_k is

$$\text{P(}{C}_k|x_n)=\frac{1}{1+e^{-a_k}}.$$

The value a_k is the weighted sum of all the units that are connected to class k. Performing multilabel classification requires a sigmoid layer followed by a custom binary cross-entropy loss layer.

Layer Input and Output Formats

Layers in a layer array or layer graph pass data to subsequent layers as formatted dlarray objects. The format of a dlarray object is a string of characters, in which each character describes the corresponding dimension of the data. The formats consist of one or more of these characters:

• "S" — Spatial

• "C" — Channel

• "B" — Batch

• "T" — Time

• "U" — Unspecified

For example, 2-D image data that is represented as a 4-D array, where the first two dimensions correspond to the spatial dimensions of the images, the third dimension corresponds to the channels of the images, and the fourth dimension corresponds to the batch dimension, can be described as having the format "SSCB" (spatial, spatial, channel, batch).

SigmoidLayer objects apply an element-wise operation and supports input data of any format. The layer and does not add or remove any dimensions, so it outputs data with the same format as its inputs.

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 R2020b