Softmax Layer

Softmax layer

Since R2024b

• 

Libraries:
Deep Learning Toolbox / Deep Learning Layers / Activation Layers

Description

The Softmax Layer block applies a softmax function to layer input. The input data must follow the data format that you specify with the Data format block parameter.

The exportNetworkToSimulink function generates this block to represent a softmaxLayer object.

Limitations

• If you specify a data format that contains Spatial (S) dimensions, the spatial dimensions of the input data must be singleton dimensions.

Ports

Input

Port_1 — Input data

scalar | vector | matrix

The matrix to which to apply the softmax function. The data must have the format that you specify with the Data format block parameter.

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

Output

Port_1 — Output data

scalar | vector | matrix

The result of applying the softmax function on the input matrix. The output data uses the format that you specify with the Data format block parameter.

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

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Main

Data format — Format of input data

C (default) | CT | SC | SSC | SSSC

Data format for the input data. The options use the same notation as the fmt argument of the dlarray object, except layer blocks do not support the Batch (B) dimension and instead assume an observation number of 1.

Programmatic Use

Block Parameter: DataFormat

Type: character vector

Values: C | 'CT' | 'SC' | 'SSC' | 'SSSC'

Default: 'C'

Data Types

Approximation method — Approximation method for computing layer output

None (default) | Lookup

Specify the type of approximation for computing the output.

Approximation Method	Data Types Supported	When to Use This Method
None (default)	Floating-point	You are processing only floating-point data.
Lookup	Floating-point and fixed-point	You are processing fixed-point data.

Programmatic Use

Block Parameter: ApproximationMethod

Type: character vector

Values: 'none' | 'Lookup'

Default: 'none'

Output minimum — Minimum output value for range checking

[] (default) | scalar

Minimum value of the output range that the software checks.

The software uses the minimum value to perform:

• Parameter range checking for some blocks. For more information, see Specify Minimum and Maximum Values for Block Parameters (Simulink).

• Simulation range checking. For more information, see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink).

• Automatic scaling of fixed-point data types.

• Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as SIL or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).

Tips

Output minimum does not saturate or clip the actual output signal. Use the Saturation (Simulink) block instead.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	OutMin
Values:	'[]' (default) | scalar in quotes

Output maximum — Maximum output value for range checking

[] (default) | scalar

Maximum value of the output range that the software checks.

The software uses the maximum value to perform:

• Parameter range checking for some blocks. For more information, see Specify Minimum and Maximum Values for Block Parameters (Simulink).

• Simulation range checking. For more information, see Specify Signal Ranges (Simulink) and Enable Simulation Range Checking (Simulink).

• Automatic scaling of fixed-point data types.

• Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes, such as SIL or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).

Tips

Output maximum does not saturate or clip the actual output signal. Use the Saturation (Simulink) block instead.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	OutMax
Values:	'[]' (default) | scalar in quotes

Output data type — Data type of output

Inherit: Inherit via internal rule (default) | Inherit: Keep MSB | Inherit: Match scaling | Inherit: Inherit via back propagation | Inherit: Same as first input | <data type expression>

Choose the data type for the output. The type can be inherited, specified directly, or expressed as a data type object such as Simulink.NumericType. When you select Inherit: Inherit via internal rule, Simulink chooses a data type to balance numerical accuracy, performance, and generated code size, while taking into account the properties of the embedded target hardware.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	OutDataTypeStr
Values:	'Inherit: Inherit via internal rule' (default) | 'Inherit: Keep MSB' | 'Inherit: Match scaling' | 'Inherit: Inherit via back propagation' | 'Inherit: Same as first input' | <data type expression>

Lock output data type setting against changes by the fixed-point tools — Option to prevent fixed-point tools from overriding Output data type

off (default) | on

Select this parameter to prevent the fixed-point tools from overriding the Output data type you specify on the block. For more information, see Use Lock Output Data Type Setting (Fixed-Point Designer).

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	LockScale
Values:	'off' (default) | 'on'

Output integer rounding mode — Rounding mode for fixed-point output cast operation

Floor (default) | Ceiling | Convergent | Nearest | Round | Simplest | Zero

Specify the rounding mode for the output value of the block, generated by the final fixed-point cast operation. For the rounding mode for the other internal block operations, see Internal integer rounding mode. For more information, see Rounding Modes (Fixed-Point Designer).

Block parameters always round to the nearest representable value. To control the rounding of a block parameter, enter an expression using a MATLAB^® rounding function in the mask field.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	RndMeth
Values:	'Floor' (default) | 'Ceiling' | 'Convergent' | 'Nearest' | 'Round' | 'Simplest' | 'Zero'

Output saturate on integer overflow — Method of overflow action for output cast operation

off (default) | on

Specify whether integer overflows saturate or wrap for the output value of the block, generated by the final fixed-point cast operation. For the method of overflow action of the internal block operations, see Internal saturate on integer overflow.

• on — Overflows saturate to either the minimum or maximum value that the data type can represent.

• off — Overflows wrap to the appropriate value that the data type can represent.

For example, the maximum value that the signed 8-bit integer int8 can represent is 127. Any block operation result greater than the maximum value causes overflow of the 8-bit integer.

• With this parameter selected, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of –128.

• With this parameter cleared, the software interprets the overflow-causing value as int8, which can produce an unintended result. For example, a block result of 130 (binary 1000 0010) expressed as int8 is –126.

Tips

• Set this parameter to on when your model has a possible overflow and you want explicit saturation protection in the generated code.

• To optimize the efficiency of your generated code, keep the default off setting for this parameter. Using the default setting also helps you avoid overspecifying how the block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors (Simulink).

• When you select this parameter, saturation applies to only the output or the result.

• In general, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	SaturateOnIntegerOverflow
Values:	'off' (default) | 'on'

Accumulator data type — Data type of accumulator

Inherit: Inherit via internal rule (default) | Inherit: Same as first input | <data type expression>

Choose the data type for the accumulator. The type can be inherited, specified directly, or expressed as a data type object such as Simulink.NumericType. When you select Inherit: Inherit via internal rule, Simulink chooses a data type to balance numerical accuracy, performance, and generated code size, while taking into account the properties of the embedded target hardware.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	OutDataTypeStr
Values:	'Inherit: Inherit via internal rule' (default) | 'Inherit: Same as first input' | <data type expression>

Internal integer rounding mode — Rounding mode for internal fixed-point operations

Floor (default) | Ceiling | Convergent | Nearest | Round | Simplest | Zero

Specify the rounding mode for internal fixed-point computations except for the output operation. For the rounding mode of the output operation, see Output integer rounding mode. For more information, see Rounding Modes (Fixed-Point Designer).

Block parameters always round to the nearest representable value. To control the rounding of a block parameter, enter an expression using a MATLAB rounding function in the mask field.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	InternalRndMeth
Values:	'Floor' (default) | 'Ceiling' | 'Convergent' | 'Nearest' | 'Round' | 'Simplest' | 'Zero'

Internal saturate on integer overflow — Method of overflow action for internal block operations

off (default) | on

Specify whether integer overflows saturate or wrap for the internal operations of the block. For the method of overflow action of the block output, see Output saturate on integer overflow.

• on — Overflows saturate to either the minimum or maximum value that the data type can represent.

• off — Overflows wrap to the appropriate value that the data type can represent.

For example, the maximum value that the signed 8-bit integer int8 can represent is 127. Any block operation result greater than the maximum value causes overflow of the 8-bit integer.

• With this parameter selected, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of –128.

• With this parameter cleared, the software interprets the overflow-causing value as int8, which can produce an unintended result. For example, a block result of 130 (binary 1000 0010) expressed as int8 is –126.

Tips

• Set this parameter to on when your model has a possible overflow and you want explicit saturation protection in the generated code.

• To optimize the efficiency of your generated code, keep the default off setting for this parameter. Using the default setting also helps you avoid overspecifying how the block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors (Simulink).

• When you select this parameter, saturation applies just to internal operations of the block.

• In general, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter:	InternalSaturateOnIntegerOverflow
Values:	'off' (default) | 'on'

Execution

Sample time — Option to specify sample time

-1 (default) | scalar

Specify the discrete interval between sample time hits or specify another type of sample time, such as continuous (0) or inherited (-1). For more options, see Types of Sample Time (Simulink).

By default, the block inherits its sample time based on the context of the block within the model.

Programmatic Use

To set the block parameter value programmatically, use the set_param (Simulink) function.

Parameter: SampleTime

Data Types: char

Values: '-1' (default) | scalar

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2024b

R2025a: Updated integer rounding mode and saturate on integer overflow parameters

The Integer rounding mode and Saturate integer overflow parameters are now split into output and internal versions of the parameters. Output integer rounding mode and Output saturate on integer overflow control the behavior of the final cast operation of the output of the block. Internal integer rounding mode and Internal saturate on integer overflow control the internal block operations.