Main Content

Diff. Sigmoidal MF

Difference of two sigmoids membership function

  • Diff. Sigmoidal MF block

Libraries:
Fuzzy Logic Toolbox / Membership Functions

Description

The Diff. Sigmoidal MF block implements a membership function in Simulink® based on the difference between two sigmoids. The sigmoid curves are defined by the following equation.

f(x;ak,ck)=11+eak(xck)

where k = 1,2. The parameters a1 and a2 control the slopes of the left and right curves. The parameters c1 and c2 control the points of inflection for the left and right curves.

To define a unimodal membership function with a maximum value of 1, specify the same signs for a1 and a2, and select c values far enough apart to allow for both transition areas to reach 1.

This block is related to the Sigmoidal MF and Prod. Sigmoidal MF membership function blocks.

Ports

Input

expand all

Input value for which to compute membership values, specified as a scalar or vector.

Output

expand all

Membership value, returned as a scalar or a vector. The dimensions of MF match the dimensions of x. Each element of MF is the membership value computed for the corresponding element of x.

Parameters

expand all

Parameter a1 that controls the transition area shape for the left curve. The magnitude of a1 controls the width of the transition area.

When the sign of a1 is positive, the curve increases from left to right. Conversely, when the sign of a1 is negative, the curve decreases from left to right.

Programmatic Use

Block Parameter: a1
Type: string, character vector
Default: "3"

Transition area center c1 for the left curve.

Programmatic Use

Block Parameter: c1
Type: string, character vector
Default: "-5"

Parameter a2 that controls the transition area shape for the right curve. The magnitude of a2 controls the width of the transition area.

When the sign of a2 is positive, the curve increases from left to right. Conversely, when the sign of a2 is negative, the curve decreases from left to right.

Programmatic Use

Block Parameter: a2
Type: string, character vector
Default: "1"

Transition area center c2 for the right curve.

Programmatic Use

Block Parameter: c2
Type: string, character vector
Default: "5"

Extended Capabilities

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

PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.

Version History

Introduced before R2006a

See Also

Functions