33412283 solving-fuzzy-logic-problems-with-matlab

Solving Fuzzy Logic Problems
With MATLAB

Authors:

Behnood Rahmani
Hamed Rafezi

Lotfi Zadeh, who is considered to be the father of fuzzy logic, once remarked: “In almost every
case you can build the same product without fuzzy logic, but fuzzy is faster and cheaper.”

ACKNOWLEDGEMENT

The authors would like to express their sincere thanks to Professor A.A. Khayyat for
His help and support during the course of Fuzzy Systems and Control.

Authors E-mail addresses: behnood@kish.sharif.edu (B. Rahmani), rafezi@kish.sharif.edu (H. Rafezi)

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1 CONTENTS

2 What Is Fuzzy Logic Toolbox? ........................................................................................................................ 3

2.1 Fuzzy Logic Toolbox Description ........................................................................................................... 3

3 What Is Fuzzy Logic? ...................................................................................................................................... 4

3.1 Description of Fuzzy Logic ..................................................................................................................... 4

4 Why Use Fuzzy Logic? .................................................................................................................................... 7

5 When Not to Use Fuzzy Logic......................................................................................................................... 7

6 What Can Fuzzy Logic Toolbox Do? ............................................................................................................... 8

7 Getting Started .............................................................................................................................................. 9

7.1 The Inverted Pendulum Problem description ....................................................................................... 9

8 Fuzzy Inference System:............................................................................................................................... 15

8.1 The FIS Editor ...................................................................................................................................... 15

8.2 The FIS Structure ................................................................................................................................. 17

8.3 Manipulating FIS from command line ................................................................................................. 18

8.4 Membership Functions in Fuzzy Logic Toolbox ................................................................................... 21

8.5 The Rule Editor .................................................................................................................................... 22
8.5.1 Manipulating rules from command line ....................................................................... 24

8.6 7-6- The Rule Viewer ........................................................................................................................... 24

8.7 The Surface Viewer ............................................................................................................................. 26

8.8 Some other useful commands: ........................................................................................................... 27

8.9 FIS Evaluation ...................................................................................................................................... 29

9 Building Your Own Fuzzy Simulink Models .................................................................................................. 29

10 "Inverted Pendulum and Cart" FIS design and Simulation ........................................................................... 31

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2 WHAT IS FUZZY LOGIC TOOLBOX?

2.1 FUZZY LOGIC TOOLBOX DESCRIPTION

Fuzzy Logic Toolbox is a collection of functions built on the MATLAB® numeric computing
environment. It provides tools for you to create and edit fuzzy inference systems within the
framework of MATLAB, or if you prefer, you can integrate your fuzzy systems into simula-
tions with Simulink®. You can even build stand-alone C programs that call on fuzzy systems
you build with MATLAB. This toolbox relies heavily on graphical user interface (GUI) tools to
help you accomplish your work, although you can work entirely from the command line if
you prefer.

The toolbox provides three categories of tools:

• Command line functions
• Graphical interactive tools
• Simulink blocks and examples

The first category of tools is made up of functions that you can call from the command line
or from your own applications. Many of these functions are MATLAB M-files, series of MAT-
LAB statements that implement specialized fuzzy logic algorithms. You can view the MATLAB
code for these functions using the statement

>> type function_name

You can change the way any toolbox function works by copying and renaming the M-file,
then modifying your copy. You can also extend the toolbox by adding your own M-files.

Secondly, the toolbox provides a number of interactive tools that let you access many of the
functions through a GUI. Together, the GUI-based tools provide an environment for fuzzy
inference system design, analysis, and implementation.

The third category of tools is a set of blocks for use with the Simulink simulation software.
These are specifically designed for high speed fuzzy logic inference in the Simulink environ-
ment.

What makes Fuzzy Logic Toolbox so powerful is the fact that most of human reasoning and
concept formation is linked to the use of fuzzy rules. By providing a systematic framework
for computing with fuzzy rules, Fuzzy Logic Toolbox greatly amplifies the power of human
reasoning. Further amplification results from the use of MATLAB and graphical user inter-
faces, areas in which The MathWorks™ has unparalleled expertise.

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3 WHAT IS FUZZY LOGIC?

3.1 DESCRIPTION OF FUZZY LOGIC

In recent years, the number and variety of applications of fuzzy logic have increased signifi-
cantly. The applications range from consumer products such as cameras, camcorders, wash-
ing machines, and microwave ovens to industrial process control, medical instrumentation,
decision-support systems, and portfolio selection.

To understand why use of fuzzy logic has grown, you must first understand what is meant by
fuzzy logic.

Fuzzy logic has two different meanings. In a narrow sense, fuzzy logic is a logical system,
which is an extension of multivalued logic. However, in a wider sense fuzzy logic (FL) is al-
most synonymous with the theory of fuzzy sets, a theory which relates to classes of objects
with unsharp boundaries in which membership is a matter of degree. In this perspective,
fuzzy logic in its narrow sense is a branch of FL. Even in its more narrow definition, fuzzy log-
ic differs both in concept and substance from traditional multivalued logical systems.

In Fuzzy Logic Toolbox, fuzzy logic should be interpreted as FL, that is, fuzzy logic in its wide
sense. The basic ideas underlying FL are explained very clearly and insightfully in the Intro-
duction. What might be added is that the basic concept underlying FL is that of a linguistic
variable, that is, a variable whose values are words rather than numbers. In effect, much of
FL may be viewed as a methodology for computing with words rather than numbers. Al-
though words are inherently less precise than numbers, their use is closer to human intui-
tion. Furthermore, computing with words exploits the tolerance for imprecision and thereby
lowers the cost of solution.

Another basic concept in FL, which plays a central role in most of its applications, is that of a
fuzzy if-then rule or, simply, fuzzy rule. Although rule-based systems have a long history of
use in AI, what is missing in such systems is a mechanism for dealing with fuzzy consequents
and fuzzy antecedents. In fuzzy logic, this mechanism is provided by the calculus of fuzzy
rules. The calculus of fuzzy rules serves as a basis for what might be called the Fuzzy Depen-
dency and Command Language (FDCL). Although FDCL is not used explicitly in Fuzzy Logic
Toolbox, it is effectively one of its principal constituents. In most of the applications of fuzzy
logic, a fuzzy logic solution is, in reality, a translation of a human solution into FDCL.

A trend that is growing in visibility relates to the use of fuzzy logic in combination with neu-
rocomputing and genetic algorithms. More generally, fuzzy logic, neurocomputing, and ge-
netic algorithms may be viewed as the principal constituents of what might be called soft
computing.

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Unlike the traditional, hard computing, soft computing accommodates the imprecision of
the real world. The guiding principle of soft computing is: Exploit the tolerance for impreci-
sion, uncertainty, and partial truth to achieve tractability, robustness, and low solution cost.
In the future, soft computing could play an increasingly important role in the conception
and design of systems whose MIQ (Machine IQ) is much higher than that of systems de-
signed by conventional methods.

Among various combinations of methodologies in soft computing, the one that has highest
visibility at this juncture is that of fuzzy logic and neurocomputing, leading to neuro-fuzzy
systems. Within fuzzy logic, such systems play a particularly important role in the induction
of rules from observations. An effective method developed by Dr. Roger Jang for this pur-
pose is called ANFIS (Adaptive Neuro-Fuzzy Inference System). This method is an important
component of Fuzzy Logic Toolbox.

Fuzzy logic is all about the relative importance of precision: How important is it to be exactly
right when a rough answer will do? Fuzzy Logic Toolbox for use with MATLAB is a tool for
solving problems with fuzzy logic. Fuzzy logic is a fascinating area of research because it
does a good job of trading off between significance and precision—something that humans
have been managing for a very long time.

In this sense, fuzzy logic is both old and new because, although the modern and methodical
science of fuzzy logic is still young, the concept of fuzzy logic relies on age-old skills of hu-
man reasoning.

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Fuzzy logic is a convenient way to map an input space to an output space. Mapping input to
output is the starting point for everything. Consider the following examples:

 With information about how good your service was at a restaurant, a fuzzy logic sys-
tem can tell you what the tip should be.
 With your specification of how hot you want the water, a fuzzy logic system can ad-
just the faucet valve to the right setting.
 With information about how far away the subject of your photograph is, a fuzzy logic
system can focus the lens for you.
 With information about how fast the car is going and how hard the motor is working,
a fuzzy logic system can shift gears for you.

A graphical example of an input-output map is shown in the following figure.

Figure 1- An input-Output map for the inverted pendulum problem

To determine the appropriate amount of tip requires mapping inputs to the appropriate
outputs. Between the input and the output, the preceding figure shows a black box that can
contain any number of things: fuzzy systems, linear systems, expert systems, neural net-
works, differential equations, interpolated multidimensional lookup tables, or even a spiri-
tual advisor, just to name a few of the possible options. Clearly the list could go on and on.

Of the dozens of ways to make the black box work, it turns out that fuzzy is often the very
best way. Why should that be? As Lotfi Zadeh, who is considered to be the father of fuzzy
logic, once remarked: “In almost every case you can build the same product without fuzzy
logic, but fuzzy is faster and cheaper.”

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4 WHY USE FUZZY LOGIC?

Here is a list of general observations about fuzzy logic:

 Fuzzy logic is conceptually easy to understand. The mathematical concepts behind
fuzzy reasoning are very simple. Fuzzy logic is a more intuitive approach without the
far-reaching complexity.
 Fuzzy logic is flexible. With any given system, it is easy to layer on more functionality
without starting again from scratch.
 Fuzzy logic is tolerant of imprecise data. Everything is imprecise if you look closely
enough, but more than that, most things are imprecise even on careful inspection.
Fuzzy reasoning builds this understanding into the process rather than tacking it
onto the end.
 Fuzzy logic can model nonlinear functions of arbitrary complexity. You can create a
fuzzy system to match any set of input-output data. This process is made particularly
easy by adaptive techniques like Adaptive Neuro-Fuzzy Inference Systems (ANFIS),
which are available in Fuzzy Logic Toolbox.
 Fuzzy logic can be built on top of the experience of experts. In direct contrast to
neural networks, which take training data and generate opaque, impenetrable mod-
els, fuzzy logic lets you rely on the experience of people who already understand
your system.
 Fuzzy logic can be blended with conventional control techniques. Fuzzy systems
don’t necessarily replace conventional control methods. In many cases fuzzy systems
augment them and simplify their implementation.
 Fuzzy logic is based on natural language. The basis for fuzzy logic is the basis for hu-
man communication. This observation underpins many of the other statements
about fuzzy logic.

Because fuzzy logic is built on the structures of qualitative description used in everyday lan-
guage, fuzzy logic is easy to use.

The last statement is perhaps the most important one and deserves more discussion. Natu-
ral language, which is used by ordinary people on a daily basis, has been shaped by thou-
sands of years of human history to be convenient and efficient. Sentences written in ordi-
nary language represent a triumph of efficient communication.

5 WHEN NOT TO USE FUZZY LOGIC

Fuzzy logic is not a cure-all. When should you not use fuzzy logic? The safest statement is
the first one made in this introduction: fuzzy logic is a convenient way to map an input space
to an output space. If you find it’s not convenient, try something else. If a simpler solution
already exists, use it. Fuzzy logic is the codification of common sense — use common sense

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when you implement it and you will probably make the right decision. Many controllers, for
example, do a fine job without using fuzzy logic. However, if you take the time to become
familiar with fuzzy logic, you’ll see it can be a very powerful tool for dealing quickly and effi-
ciently with imprecision and nonlinearity.

6 WHAT CAN FUZZY LOGIC TOOLBOX DO?

Fuzzy Logic Toolbox allows you to do several things, but the most important thing it lets you
do is create and edit fuzzy inference systems. You can create these systems using graphical
tools or command-line functions, or you can generate them automatically using either clus-
tering or adaptive neuro-fuzzy techniques.

If you have access to Simulink, you can easily test your fuzzy system in a block diagram simu-
lation environment.

The toolbox also lets you run your own stand-alone C programs directly, without the need
for Simulink. This is made possible by a stand-alone Fuzzy Inference Engine that reads the
fuzzy systems saved from a MATLAB session.

You can customize the stand-alone engine to build fuzzy inference into your own code. All
provided code is ANSI compliant.

Figure 2. Fuzzy Logic Toolbox Interaction Structure

Because of the integrated nature of the MATLAB environment, you can create your own
tools to customize Fuzzy Logic Toolbox or harness it with another toolbox, such as the Con-

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trol System Toolbox, Neural Network Toolbox, or Optimization Toolbox, to mention only a
few of the possibilities.

7 GETTING STARTED

We’ll start with a basic description of a two-input, one-output inverted pendulum problem.

7.1 THE INVERTED PENDULUM PROBLEM DESCRIPTION

It is interesting to note that, with practice, humans can solve the inverted pendulum prob-
lem based solely on naive physics and common sense rather than on complicated mathe-
matical models. Balancing a broom upright in your hand, as in Figure(3) for example, in-
volves more degrees of freedom and is inherently much more complicated than the inverted
pendulum on a cart depicted in Figure(4).

Figure 3. Balancing inverted pendulum

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However, when you balance the broom, you are clearly not relying on a mathematical mod-
el that depends on accurate measurements of angles and velocity. For the inverted pendu-
lum problem, it is possible to design a successful controller without knowing or using the
plant dynamics. The implication is that, in a case where plant dynamics are not available, we
can use this new technique to construct control laws.

Figure 4- Inverted Pendulum System

To balance an upright pendulum, we know from naive physics that the control force u(t)
should be chosen according to the magnitudes of the input variables θ(t) and θ'(t) that
measure the angle from the upright position and the angular velocity. The relation between
these variables is linguistic, a much weaker form than differential equations. That is exactly
what happens in a human mind that processes information qualitatively. Humans choose
u(t) by using common sense knowledge in the form of "If. . . then. . . . rules", such as "If θ is
very small and θ' is also small then u should be small," or "If the pendulum is in a balanced
position, then hold very still, that is, do not apply any force". By taking all such rules into ac-
count, the inverted pendulum can be successfully controlled.

Now, in order to create an automatic control strategy duplicating human ability, it is neces-
sary to be able to translate the above "If . . . then. . . "rules into some soft mathematical
forms for machine processing. Looking at these "If . . . then. . . " rules, we ask ourselves
questions like the following:

 Is "If. . . then. . ." an implication operator in logic?
 How can one model linguistic labels like "small," "medium," and "large"?

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 Given a finite number of "If. . . then. . ." rules, how can we handle all possible numer-
ical inputs that will be measured by machine sensors, in order to produce actual con-
trol actions?

The answers to all these basic questions lie in fuzzy logic theory. The term "fuzzy control"
refers to the science of building fuzzy controllers based on the mathematics of fuzzy logic.

Now let us look in more detail at the design of a fuzzy controller for the inverted pendulum
on a cart. The input to the controller is the pair (θ, θ'). Let us take the input space to be X×Y,
where X and Y are intervals representing degrees for θ and degrees per second for θ'. The
output or control space for u is an interval representing Newtons for u. The linguistic labels
are modeled as fuzzy subsets of the spaces X, Y , and U by specifying their membership func-
tions. For example, these linguistic labels could correspond to negative big (NB), negative
medium (NM), negative small (NS), positive small (PS), positivemedium (PM), and positive
big (PB).

Figure 5- Fuzzy sets Aj for "angle"”

Figure 6- Fuzzy sets Bj for "angular velocity"

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Figure 7- Fuzzy sets Cj for "force"

The particular choice of membership functions chosen to represent the linguistic labels is
somewhat arbitrary. One of the adjustments made during testing of the control system will
be experimenting with different membership functions, that is, changing the parameters of
these triangular functions. This process is called tuning.

The rules are then of the form

1. If angle is negative medium and velocity is positive small then force is negative small.
2. If angle is negative medium and velocity is positive medium then force is positive
small.
3. If angle is negative small and velocity is positive medium then force is positive small.

and so forth. With six membership functions for each of X and Y, we can have 36 rules of the
form

Rj : If θ is Aj and θ' is Bj then u is Cj

where Aj , Bj, and Cj are the fuzzy subsets of X, Y and U depicted above.

The look-up table summarizes 36 possible rules in a compact form.

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Figure 8- Inverted pendulum look-up table

The input (θ, θ’) to each rule Rj will result in a fuzzy subset of U. This fuzzy subset is often
taken to be the minimum:

The fusion of rules, via the maximum, produces a fuzzy subset of U representing a control
action:

If, for example, the measurements are θ = −8° and θ’ = 2°/ s then the fuzzy sets depicted
above give the values:

and all other Ai and Bi are zero at this point. Thus the only rules pertinent for this input are
the four:

as all others give the value zero for this input. These four rules are said to "fire" for this in-
put.

Combining these rules, we have the fuzzy set:

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and the aggregated output is the following fuzzy subset of U:

To produce an actual control action for the input (θ, θ’), we need to summarize the fuzzy
subset Ψ(u) in some way. The control action depends on the defuzzification technique that
is applied to this fuzzy set. A natural choice is the centroid defuzzification method namely;
the actual control value is taken to be:

The control methodology described above, with sufficient tuning, will lead to successful con-
trol of the inverted pendulum.

The methodology of fuzzy control consists of selecting and using:

1. a collection of rules that describe the control strategy,
2. membership functions for the linguistic labels in the rules,
3. logical connectives for fuzzy relations, and
4. A defuzzification method.

At the end, the derived control law is the realization of a function ϕ from X to U, the space
of control variables.

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8 FUZZY INFERENCE SYSTEM:

8.1 THE FIS EDITOR

Figure 9- Upper part of "FIS Editor"

The FIS Editor displays general information about a fuzzy inference system. There is a simple
diagram at the top that shows the names of each input variable on the left, and those of
each output variable on the right. The sample membership functions shown in the boxes are
just icons and do not depict the actual shapes of the membership functions:

 Below the diagram is the name of the system and the type of inference used. The de-
fault, Mamdani-type inference, is what is described so far and what you continue to
use for this example.

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Figure 10- Lower part of "FIS Editor"

 Below the name of the fuzzy inference system, on the left side of the figure, are the
pop-up menus that allow you to modify the various pieces of the inference process.
 On the right side at the bottom of the figure is the area that displays the name of ei-
ther an input or output variable, its associated membership function type, and its
range.
 The latter two fields are specified only after the membership functions have been.
 Below that region are the Help and Close buttons that call up online help and close
the window, respectively. At the bottom is a status line that relays information about
the system.

To start this system from scratch, type:

>> fuzzy

at the MATLAB prompt. The generic untitled FIS Editor opens, with one input, labeled in-
put1, and one output, labeled output1. For this example, you construct a two-input, one
output system. A second yellow box labeled input2 appears. The two inputs in your example
are Theta and Theta dot. The one output is Force. You want to change the variable names
to reflect these designations:

1. Select Edit > Add variable > Input.
2. Click the yellow box input1. This box is highlighted with a red outline.
3. Edit the Name field from input1 to Theta, and press Enter.
4. Click the yellow box input2. This box is highlighted with a red outline.

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5. Edit the Name field from input2 to Theta dot, and press Enter.
6. Click the blue box output1.
7. Edit the Name field from output1 to Force, and press Enter.
8. Select File > Export > To Workspace.

Figure 11- Export Dialog Box

9. Enter the Workspace variable name Inverted pendulum , and click OK.

The diagram is updated to reflect the new names of the input and output variables. There is
now a new variable in the workspace called tipper that contains all the information about
this system. By saving to the workspace with a new name, you also rename the entire sys-
tem. Your window looks something like the following diagram.

8.2 THE FIS STRUCTURE

The FIS structure is the MATLAB object that contains all the fuzzy inference system informa-
tion. This structure is stored inside each GUI tool. Access functions such as getfis and setfis
make it easy to examine this structure. All the information for a given fuzzy inference sys-
tem is contained in the FIS structure, including variable names, membership function defini-
tions, and so on. This structure can itself be thought of as a hierarchy of structures, as
shown in the following diagram.

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Figure 12- Structure of Fuzzy Inference System (FIS)

8.3 MANIPULATING FIS FROM COMMAND LINE

1. Create new Fuzzy Inference System:

>> a=newfis('Inverted Pendulum');

2. Create and Name input(s):

>> a.input(1).name='Theta';

3. Determine input(s) range:

>> a.input(1).range=[-1.5 1.5];

4. Create and Name input membership function(s):

>> a.input(1).mf(1).name='NL';

5. Determine input MF(s) type:

>> a.input(1).mf(1).type='trimf';

6. Determine selected MF(s) parameters:

>> a.input(1).mf(1).params=[-1.5 -1.5 -1];

7. Create and Name output:

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>> a.output(1).name='Force';

8. Determine output range:

>> a.output(1).range=[-90 90];

9. Create and name output MF(s):

>> a.output(1).mf(1).name='PL'

10. Determine output MF(s) type:

>> a.output(1).mf(1).type='trimf';

11. Determine selected MF(s) parameters:

>> a.output(1).mf(1).params=[60 90 90];

Alternatively, you can build the entire inverted pendulum system from the command line
using Fuzzy Logic Toolbox commands.

>> a=newfis('Inverted Pendulum');

>> a=addvar(a,'input','Theta',[-1.5 1.5]);

>> a=addmf(a,'input',1,'NL','trimf',[-1.5 -1.5 -1]);

...

>> a=addvar(a,'output','Force',[-90 90]);

>> a=addmf(a,'output',1,'PL','trimf',[60 90 90]);

…

12. Remove variables from Fuzzy Inference System:

>> b = rmvar(a,'input',1);

13. Remove membership function from Fuzzy Inference System:

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>> b = rmmf(a,'input',1,'mf',1);

14. Fuzzy system properties

>> getfis(a)
Name = Inverted Pendulum
Type = mamdani
NumInputs = 2
InLabels =
Theta
Thetadot
NumOutputs = 1
OutLabels =
Force
NumRules = 49
AndMethod = prod
OrMethod = max
ImpMethod = min
AggMethod = max
DefuzzMethod = centroid

ans =

Inverted Pendulum

15. Load Fuzzy Inference System from file:

>> a=readfis('invp.fis')

a=
name: ' Inverted Pendulum '
type: 'mamdani'

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andMethod: 'prod'
orMethod: 'max'
defuzzMethod: 'centroid'
impMethod: 'min'
aggMethod: 'max'
input: [1x2 struct]
output: [1x1 struct]
rule: [1x49 struct]

16. Save Fuzzy Inference System to file:

>> writefis(fismat,'filename')

8.4 MEMBERSHIP FUNCTIONS IN FUZZY LOGIC TOOLBOX

The only condition a membership function must really satisfy is that it must vary between 0
and 1. The function itself can be an arbitrary curve whose shape we can define as a function
that suits us from the point of view of simplicity, convenience, speed, and efficiency.

A fuzzy set is an extension of a classical set. If X is the universe of discourse and its elements
are denoted by x, then a fuzzy set A in X is defined as a set of ordered pairs.

A = {x, μA(x) | x X}

μA(x) is called the membership function (or MF) of x in A. The membership function maps
each element of X to a membership value between 0 and 1.

Fuzzy Logic Toolbox includes 11 built-in membership function types. These 11 functions are,
in turn, built from several basic functions:

• piecewise linear functions
• the Gaussian distribution function
• the sigmoid curve
• quadratic and cubic polynomial curves

The simplest membership functions are formed using straight lines. Of these, the simplest is
the triangular membership function, and it has the function name trimf. This function is
nothing more than a collection of three points forming a triangle. The trapezoidal member-
ship function, trapmf, has a flat top and really is just a truncated triangle curve. These
straight line membership functions have the advantage of simplicity.

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MF type Description

Dsigmf Built-in membership function composed of difference between two sigmoidal membership
functions

Gauss2mf Gaussian combination membership function

Gaussmf Gaussian curve built-in membership function

Gbellmf Generalized bell-shaped built-in membership function

Pimf П -shaped built-in membership function
Psigmf Built-in membership function composed of product of two sigmoidally shaped membership
functions

Sigmf Sigmoidally shaped built-in membership function

Smf S-shaped built-in membership function

Trapmf Trapezoidal-shaped built-in membership function

Trimf Triangular-shaped built-in membership function

Zmf Z-shaped built-in membership function

8.5 THE RULE EDITOR

Constructing rules using the graphical Rule Editor interface is fairly self evident. Based on
the descriptions of the input and output variables defined with the FIS Editor, the Rule Edi-
tor allows you to construct the rule statements automatically, From the GUI, you can:

• Create rules by selecting an item in each input and output variable box, and one
Connection item and clicking Add Rule. You can choose none as one of the variable
qualities to exclude that variable from a given rule and choose not under any varia-
ble name to negate the associated quality.
• Delete a rule by selecting the rule and clicking Delete Rule.
• Edit a rule by changing the selection in the variable box and clicking Change Rule.
• Specify weight to a rule by typing in a desired number between 0 and 1 in Weight. If
you do not specify the weight, it is assumed to be unity (1).

Similar to those in the FIS Editor and the Membership Function Editor, the Rule Editor has
the menu bar and the status line. The menu items allow you to open, close, save and edit a
fuzzy system using the five basic GUI tools.

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Figure 13- The Rule Editor Window

From the menu, you can also:

• Set the format for the display by selecting Options > Format.
• Set the language by selecting Options > Language.

You can access information about the Rule Editor by clicking Help and close the GUI using
Close.

To change a rule, first click on the rule to be changed. Next make the desired changes to
that rule, and then click Change rule.

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8.5.1 MANIPULATING RULES FROM COMMAND LINE

1. The initial (or "if") part of a fuzzy rule:

>>a.rule(1).antecedent=[1 1];

2. The final (or "then") part of a fuzzy rule:

>>a.rule(1).consequent=[1];

8.6 7-6- THE RULE VIEWER

Figure 14- Rule Viewer Window

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The Rule Viewer displays a roadmap of the whole fuzzy inference process. It is based on the
fuzzy inference diagram described in the previous section. You see a single figure window
with 10 plots nested in it. The three plots across the top of the figure represent the antece-
dent and consequent of the first rule. Each rule is a row of plots, and each column is a varia-
ble. The rule numbers are displayed on the left of each row. You can click on a rule number
to view the rule in the status line.

 The first two columns of plots (the yellow plots) show the membership functions re-
ferenced by the antecedent, or the if-part of each rule.
 The third column of plots (the blue plots) shows the membership functions refe-
renced by the consequent, or the then-part of each rule.
 The fourth plot in the third column of plots represents the aggregate weighted deci-
sion for the given inference system.

This decision will depend on the input values for the system. The defuzzified output is dis-
played as a bold vertical line on this plot.

The variables and their current values are displayed on top of the columns. In the lower left,
there is a text field Input in which you can enter specific input values. For the two-input sys-
tem, you will enter an input vector, [-0.69 -1.79], for example, and then press Enter. You can
also adjust these input values by clicking on any of the three plots for each input. This will
move the red index line horizontally, to the point where you have clicked. Alternatively, you
can also click and drag this line in order to change the input values. When you release the
line, (or after manually specifying the input), a new calculation is performed, and you can
see the whole fuzzy inference process take place:

A yellow patch of color under the actual membership function curve is used to make the
fuzzy membership value visually apparent.

The Rule Viewer shows one calculation at a time and in great detail. In this sense, it presents
a sort of micro view of the fuzzy inference system. If you want to see the entire output sur-
face of your system—the entire span of the output set based on the entire span of the input
set— you need to open up the Surface Viewer. This viewer is the last of our five basic GUI
tools in Fuzzy Logic Toolbox, and you open it by selecting Surface from the View menu.

25

8.7 THE SURFACE VIEWER

Figure 15- Surface Viewer Window

Upon opening the Surface Viewer, you see a three-dimensional curve that represents the
mapping from food and service quality to tip amount. Because this curve represents a two-
input one-output case, you can see the entire mapping in one plot. When we move beyond
three dimensions overall, we start to encounter trouble displaying the results. Accordingly,
the Surface Viewer is equipped with drop-down menus X (input):, Y (input): and Z (output):
that let you select any two inputs and any one output for plotting. Below these menus are
two input fields X grids: and Y grids: that let you specify how many x-axis and y-axis grid
lines you want to include. This capability allows you to keep the calculation time reasonable
for complex problems.

Clicking Evaluate initiates the calculation, and the plot is generated after the calculation is
complete. To change the x-axis or y-axis grid after the surface is in view, change the appro-
priate input field, and press Enter. The surface plot is updated to reflect the new grid set-

26

tings. The Surface Viewer has a special capability that is very helpful in cases with two (or
more) inputs and one output: you can grab the axes, using the mouse and reposition them
to get a different three-dimensional view on the data.

The Ref. Input field is used in situations when there are more inputs required by the system
than the surface is mapping. You can edit this field to explicitly set inputs not specified in the
surface plot.

Suppose you have a four-input one-output system and would like to see the output surface.
The Surface Viewer can generate a three-dimensional output surface where any two of the
inputs vary, but two of the inputs must be held constant because computer monitors cannot
display a five-dimensional shape. In such a case, the input is a four-dimensional vector with
NaNs holding the place of the varying inputs while numerical values indicates those values
that remain fixed. A NaN is the IEEE symbol for not a number.

8.8 SOME OTHER USEFUL COMMANDS:

 fuzzy(a) displays the FIS Editor.
 mfedit(a) displays the Membership Function Editor.
 ruleedit(a) displays the Rule Editor.
 ruleview(a) displays the Rule Viewer.
 surfview(a) displays the Surface Viewer.
 plotmf(a,'input',1) returns the following plots

Figure 16- Plot of Input Membership Functions by use of "plotmf" command

27

 plotmf(a,'output',1) returns the following plots

Figure 17- Plot of Output Membership Functions by use of "plotmf" command

 gensurf(a)

Figure 18- Plot of system Surface by use of "gensurf" command

28

8.9 FIS EVALUATION

To evaluate the output of a fuzzy system for a given input, use the function evalfis. For ex-
ample, the following script evaluates”force” of inverted pendulum at the input, [0.5 1].

>> a = readfis('Invp.fis');
>> force=evalfis([.5 1], a)

force =
21.3170

This function can also be used for multiple collections of inputs, because different input vec-
tors are represented in different parts of the input structure.

>>evalfis([.5 1; -1 2], a)

ans =

21.3170

-26.2493

9 BUILDING YOUR OWN FUZZY SIMULINK MODELS

To build your own Simulink systems that use fuzzy logic you can find the Fuzzy Logic Control-
ler block in the Fuzzy Logic Toolbox library, which you can open either by selecting Fuzzy
Logic Toolbox in the Simulink Library Browser, or by typing

fuzblock

at the MATLAB prompt.

The following library appears.

29

Figure 19- Fuzzy Logic Toolbox "Block" library

The Fuzzy Logic Toolbox library contains the Fuzzy Logic Controller and Fuzzy Logic Control-
ler with Rule Viewer blocks. It also includes a Membership Functions sublibrary that con-
tains Simulink blocks for the built-in membership functions.

The Fuzzy Logic Controller with Rule Viewer block is an extension of the Fuzzy Logic Control-
ler block. It allows you to visualize how rules are fired during simulation. Right-click on the
Fuzzy Controller With Rule Viewer block, and select Look Under Mask, and the following
window appears.

Figure 20- Fuzzy Controller with Ruleviewer

To initialize the Fuzzy Logic Controller blocks (with or without the Rule Viewer), double-click
on the block and enter the name of the structure variable describing your FIS. This variable
must be located in the MATLAB workspace.

30

10 "INVERTED PENDULUM AND CART" FIS DESIGN AND SIMULATION

The properties of “Inverted Pendulum system” which described in section() , are as follow:

 M= 2 kg
 m= 1 kg
 L= 1 m

According to previous sections, you should be able to design the FIS system to control the
“Inverted Pendulum plant”. The look up table for given system is available as follow:

Table 1- Look up table for "Inverted Pendulum System"

𝜽𝜽 NL NM NS AZ PS PM PL

NL NL NL NL NL NM NS PS

NM NL NL NM NM NS PS PS

NS NL NM NS NS PS PS PM

AZ NL NM NS AZ PS PM PL

PS NM NS NS PS PS PM PL

PM NS NS PS PM PM PL PL

PL NS PS PM PL PL PL PL

Fuzzy Logic Toolbox is designed to work with Simulink. After you have created your fuzzy
system using the GUI tools or some other method and exporting it into a structure (e.g. a) ,
you are ready to embed your system directly into a simulation.

After putting a fuzzy block from fuzzy library (which mentioned in previous sections) you
must insert provided inverted pendulum plant as a block. Next make necessary connections
such as shown below. After setting desired initial conditions for the plant, your system is
ready for simulation.

31

Figure 21- Preview of "Inverted Pendulum" control system

Figure 22- Response to initial condition

32

References

1. L.X. Wang, A Course in Fuzzy Systems and Control, Prentice-Hall

2. J.J. Buckley [2005], Simulating Fuzzy systems, Springer.

3. H.T. Nguyen, N.R. Prasad, C.L. Walker, E.A. Walker [2003], A First Course in Fuzzy and
Neural Control, Chapman & Hall/CRC.

4. The MathWorks, Inc.[2007], Fuzzy Logic Toolbox User’s Guide.

33

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