gensurf

Generate fuzzy inference system output surface

Syntax

gensurf(fis)

gensurf(fis,options)

[X,Y,Z] = gensurf(___)

Description

gensurf(fis) generates the output surface for the fuzzy inference system, fis, plotting the first output variable against the first two input variables. For fuzzy systems with more than two inputs, the remaining input variables use the midpoints of their respective ranges as reference values.

gensurf(fis,options) generates the output surface using the specified options. To generate a surface using different inputs or outputs, or to specify nondefault plotting options, use this syntax.

[X,Y,Z] = gensurf(___) returns the variables that define the output surface for any of the previous syntaxes and suppresses the surface plot.

Examples

Generate FIS Output Surface

Load a fuzzy inference system.

fis = readfis("tipper");

This fuzzy system has two inputs and one output.

Generate the output surface for the system.

gensurf(fis)

Generate FIS Output Surface for Second Output

Load a fuzzy inference system with two inputs and two outputs.

fis = readfis("mam22.fis");

Create a surface generation option set, specifying the second output as the output to plot. By default, this output is plotted against the first two input variables.

opt = gensurfOptions(OutputIndex=2);

Plot the surface, using the specified option set.

gensurf(fis,opt)

Specify Reference Inputs for Surface Plot

Load a fuzzy inference system with four inputs and one output.

fis = readfis("multiInput.fis");

Create a default gensurfOptions object..

opt = gensurfOptions;

Specify plotting options to:

• Plot the output against the second and third input variable.

• Use 20 grid points for both inputs.

• Fix the first and fourth inputs at -0.5 and 0.1 respectively. Set the reference values for the second and third inputs to NaN.

opt.InputIndex = [2 3];
opt.NumGridPoints = 20;
opt.ReferenceInputs = [-0.5 NaN NaN 0.1];

Plot the output surface.

gensurf(fis,opt)

Return Surface Values and Suppress Plot

Load a fuzzy inference system.

fis = readfis("tipper");

Generate the output surface, returning the surface data.

[X,Y,Z] = gensurf(fis);

The output values, Z, are the FIS output evaluated at the corresponding X and Y grid points.

Input Arguments

fis — Fuzzy inference system

mamfis object | sugfis object | mamfistype2 object | sugfistype2 object | fistree object

Fuzzy inference system, specified as one of these objects:

• mamfis — Mamdani fuzzy inference system

• sugfis — Sugeno fuzzy inference system

• mamfistype2 — Type-2 Mamdani fuzzy inference system

• sugfistype2 — Type-2 Sugeno fuzzy inference system

• fistree — Tree of interconnected fuzzy inference systems (since R2021b)

options — Surface generation options

gensurfOptions option set

Surface generation options, specified as a gensurfOptions option set.

Output Arguments

X — Grid values for first input variable

array | column vector

Grid values for first input variable, returned as one of the following:

• M-by-N array, where N and M are the number of grid points for the first and second inputs, respectively; that is options.NumGridPoints = [N M]. Each column of X contains one grid point value, repeated for every row.

• P-element column vector, where P is the number of grid points specified for a single input variable; that is options.NumGridPoints = P. Each element of contains one grid point value. This case applies when fis has only one input variable.

Y — Grid values for second input variable

array | []

Grid values for second input variable, returned as one of the following:

• M-by-N array, where N and M are the number of grid points for the first and second inputs respectively; that is options.NumGridPoints = [N M]. Each row of Y contains one grid point value, repeated for every column.

• [] when you specify only one input variable; that is, if you specify options.InputIndex as an integer.

Z — Surface output values

array | vector

Surface output values for the output variable of fis specified by options.OutputIndex, returned as one of the following:

• M-by-N array, where N and M are the number of grid points for the first and second inputs respectively; that is options.NumGridPoints = [N M]. Each element of Z is the value of the FIS output, evaluated at the corresponding X and Y input values. For example, for a two-input system:

  Z(i,j) = evalfis(fis,[X(i,j) Y(i,j)]);

• P-element column vector, where P is the number of grid points specified for a single input variable; that is options.NumGridPoints = P. Each element of Z is the value of the FIS output evaluated at the corresponding X input value.

When computing the value of Z, gensurf sets the values of any inputs not specified by options.InputIndex to their corresponding reference values, as specified in options.ReferenceInputs.

Alternative Functionality

App

You can interactively view the control surface for a FIS using the Fuzzy Logic Designer app.

Version History

Introduced before R2006a

R2024b: Fuzzy inference system structures not supported

gensurf no longer supports fuzzy inference system structures. Use mamfis and sugfis objects instead. To convert existing fuzzy inference system structures to objects, use the convertfis function.

R2019b: Fuzzy inference system structures will not be supported

Support for fuzzy inference systems structures will be removed in a future release. This change was announced in R2018b. Using fuzzy inference system structures with gensurf issues a warning starting in R2019b.

R2017a: Specify options using gensurfOptions

To specify options for generating fuzzy inference system output surfaces, you now create a gensurfOptions option set. You can then modify the options using dot notation. Any options you do not modify remain at their default values.

Previously, to generate an output surface for a fuzzy inference system using gensurf, you specified the generation options using optional input arguments.

gensurf(fis,inputs,output,grids,refInput,points);

Starting in R2017a, if your code uses gensurf, modify the code to use a gensurfOptions option set.

opt = gensurfOptions;
opt.InputIndex = [1 3];
fis = gensurf(fis,opt);

The following table shows the mapping of the old gensurf input arguments to the new gensurfOptions option set.

Old gensurf Input Argument	New gensurfOptions Option
inputs	InputIndex
output	OutputIndex
grids	NumGridPoints
refinput	ReferenceInputs
points	NumSamplePoints