Fuzzy Logic Toolbox

The FIS Structure

The FIS structure is the MATLAB object that contains all the fuzzy inference system information. This structure is stored inside each GUI tool. Access functions such as getfis and setfis make it easy to examine this structure. You can also access the FIS structure information using the structure.field syntax (see the section, Working from the Command Line).

All the information for a given fuzzy inference system is contained in the FIS structure, including variable names, membership function definitions, 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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You can generate a listing of information on the FIS using the showfis command, as shown below.

• showfis(a)
  1.  Name             tipper
  2.  Type             mamdani
  3.  Inputs/Outputs   [ 2 1 ]
  4.  NumInputMFs      [ 3 2 ]
  5.  NumOutputMFs     3
  6.  NumRules         3
  7.  AndMethod        min
  8.  OrMethod         max
  9.  ImpMethod        min
  10. AggMethod        max
  11. DefuzzMethod     centroid
  12. InLabels         service
  13.                  food   
  14. OutLabels        tip
  15. InRange          [ 0 10 ]
  16.                  [ 0 10 ]
  17. OutRange         [ 0 30 ]
  18. InMFLabels       poor     
  19.                  good     
  20.                  excellent
  21.                  rancid   
  22.                  delicious
  23. OutMFLabels      cheap   
  24.                  average 
  25.                  generous
  26. InMFTypes        gaussmf
  27.                  gaussmf
  28.                  gaussmf
  29.                  trapmf 
  30.                  trapmf 
  31. OutMFTypes       trimf
  32.                  trimf
  33.                  trimf
  34. InMFParams       [ 1.5 0 0 0 ] 
  35.                  [ 1.5 5 0 0 ] 
  36.                  [ 1.5 10 0 0 ]
  37.                  [ 0 0 1 3 ]   
  38.                  [ 7 9 10 10 ] 
  39. OutMFParams      [ 0 5 10 0 ]  
  40.                  [ 10 15 20 0 ]
  41.                  [ 20 25 30 0 ]
  42. Rule Antecedent  [ 1 1 ]
  43.                  [ 2 0 ]
  44.                  [ 3 2 ]
  42. Rule Consequent  1
  43.                  2
  44.                  3
  42. Rule Weigth      1
  43.                  1
  44.                  1
  42. Rule Connection  2
  43.                  1
  44.                  2
  

The list of command-line functions associated with FIS construction include getfis, setfis, showfis, addvar, addmf, addrule, rmvar, and rmmf.

Saving FIS Files on Disk

A specialized text file format is used for saving fuzzy inference systems to a disk. The functions readfis and writefis are used for reading and writing these files.

If you prefer, you can modify the FIS by editing its .fis text file rather than using any of the GUIs. You should be aware, however, that changing one entry may oblige you to change another. For example, if you delete a membership function using this method, you also need to make certain that any rules requiring this membership function are also deleted.

The rules appear in "indexed" format in a .fis text file. Here is the file tipper.fis.

• [System]
  Name='tipper'
  Type='mamdani'
  NumInputs=2
  NumOutputs=1
  NumRules=3
  AndMethod='min'
  OrMethod='max'
  ImpMethod='min'
  AggMethod='max'
  DefuzzMethod='centroid'
  
  [Input1]
  Name='service'
  Range=[0 10]
  NumMFs=3
  MF1='poor':'gaussmf',[1.5 0]
  MF2='good':'gaussmf',[1.5 5]
  MF3='excellent':'gaussmf',[1.5 10]
  
  [Input2]
  Name='food'
  Range=[0 10]
  NumMFs=2
  MF1='rancid':'trapmf',[0 0 1 3]
  MF2='delicious':'trapmf',[7 9 10 10]
  
  [Output1]
  Name='tip'
  Range=[0 30]
  NumMFs=3
  MF1='cheap':'trimf',[0 5 10]
  MF2='average':'trimf',[10 15 20]
  MF3='generous':'trimf',[20 25 30]
  
  [Rules]
  1 1, 1 (1) : 2
  2 0, 2 (1) : 1
  3 2, 3 (1) : 2
  

FIS Evaluation

Working with Simulink