Jürgen Mück > AI-FuzzyEngine-v0.2.2 > AI::FuzzyEngine

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Module Version: v0.2.2   Source  

NAME ^

AI::FuzzyEngine - A Fuzzy Engine, PDL aware

SYNOPSIS ^

Regular Perl - without PDL

    use AI::FuzzyEngine;

    # Engine (or factory) provides fuzzy logical arithmetic
    my $fe = AI::FuzzyEngine->new();

    # Disjunction:
    my $a = $fe->or ( 0.2, 0.5, 0.8, 0.7 ); # 0.8
    # Conjunction:
    my $b = $fe->and( 0.2, 0.5, 0.8, 0.7 ); # 0.2
    # Negation:
    my $c = $fe->not( 0.4 );                # 0.6
    # Always true:
    my $t = $fe->true();                    # 1.0
    # Always false:
    my $f = $fe->false();                   # 0.0

    # These functions are constitutive for the operations
    # on the fuzzy sets of the fuzzy variables:

    # VARIABLES (AI::FuzzyEngine::Variable)

    # input variables need definition of membership functions of their sets
    my $flow = $fe->new_variable( 0 => 2000,
                        small => [0, 1,  500, 1, 1000, 0                  ],
                        med   => [       400, 0, 1000, 1, 1500, 0         ],
                        huge  => [               1000, 0, 1500, 1, 2000, 1],
                   );
    my $cap  = $fe->new_variable( 0 => 1800,
                        avg   => [0, 1, 1500, 1, 1700, 0         ],
                        high  => [      1500, 0, 1700, 1, 1800, 1],
                   );
    # internal variables need sets, but no membership functions
    my $saturation = $fe->new_variable( # from => to may be ommitted
                        low   => [],
                        crit  => [],
                        over  => [],
                   );
    # But output variables need membership functions for their sets:
    my $green = $fe->new_variable( -5 => 5,
                        decrease => [-5, 1, -2, 1, 0, 0            ],
                        ok       => [       -2, 0  0, 1, 2, 0      ],
                        increase => [              0, 0, 2, 1, 5, 1],
                   );

    # Reset FuzzyEngine (resets all variables)
    $fe->reset();

    # Reset a fuzzy variable directly
    $flow->reset;

    # Membership functions can be changed via the set's variable.
    # This might be useful during parameter identification algorithms
    # Changing a function resets the respective variable.
    $flow->change_set( med => [500, 0, 1000, 1, 1500, 0] );

    # Fuzzification of input variables
    $flow->fuzzify( 600 );
    $cap->fuzzify( 1000 );

    # Membership degrees of the respective sets are now available:
    my $flow_is_small = $flow->small(); # 0.8
    my $flow_is_med   = $flow->med();   # 0.2
    my $flow_is_huge  = $flow->huge();  # 0.0

    # RULES and their application

    # a) If necessary, calculate some internal variables first. 
    # They will not be defuzzified (in fact, $saturation can't)
    # Implicit application of 'and'
    # Multiple calls to a membership function
    # are similar to 'or' operations:
    $saturation->low( $flow->small(), $cap->avg()  );
    $saturation->low( $flow->small(), $cap->high() );
    $saturation->low( $flow->med(),   $cap->high() );

    # Explicite 'or', 'and' or 'not' possible:
    $saturation->crit( $fe->or( $fe->and( $flow->med(),  $cap->avg()  ),
                                $fe->and( $flow->huge(), $cap->high() ),
                       ),
                 );
    $saturation->over( $fe->not( $flow->small() ),
                       $fe->not( $flow->med()   ),
                       $flow->huge(),
                       $cap->high(),
                 );
    $saturation->over( $flow->huge(), $fe->not( $cap->high() ) );

    # b) deduce output variable(s) (here: from internal variable $saturation)
    $green->decrease( $saturation->low()  );
    $green->ok(       $saturation->crit() );
    $green->increase( $saturation->over() );

    # All sets provide their respective membership degrees: 
    my $saturation_is_over = $saturation->over(); # This is no defuzzification!
    my $green_is_ok        = $green->ok();

    # Defuzzification ( is a matter of the fuzzy variable )
    my $delta_green = $green->defuzzify(); # -5 ... 5

Using PDL and its threading capability

    use PDL;
    use AI::FuzzyEngine;

    # (Probably a stupide example)
    my $fe        = AI::FuzzyEngine->new();

    # Declare variables as usual
    my $severity  = $fe->new_variable( 0 => 10,
                          low  => [0, 1, 3, 1, 5, 0       ],
                          high => [      3, 0, 5, 1, 10, 1],
                        );

    my $threshold = $fe->new_variable( 0 => 1,
                           low  => [0, 1, 0.2, 1, 0.8, 0,     ],
                           high => [      0.2, 0, 0.8, 1, 1, 1],
                         );
    
    my $problem   = $fe->new_variable( -0.5 => 2,
                           no  => [-0.5, 0, 0, 1, 0.5, 0, 1, 0],
                           yes => [         0, 0, 0.5, 1, 1, 1, 1.5, 1, 2, 0],
                         );

    # Input data is a pdl of arbitrary dimension
    my $data = pdl( [0, 4, 6, 10] );
    $severity->fuzzify( $data );

    # Membership degrees are piddles now:
    print 'Severity is high: ', $severity->high, "\n";
    # [0 0.5 1 1]

    # Other variables might be piddles of other dimensions,
    # but all variables must be expandible to a common 'wrapping' piddle
    # ( in this case a 4x2 matrix with 4 colums and 2 rows)
    my $level = pdl( [0.6],
                     [0.2],
                   );
    $threshold->fuzzify( $level );

    print 'Threshold is low: ', $threshold->low(), "\n";
    # [
    #  [0.33333333]
    #  [         1]
    # ]

    # Apply some rules
    $problem->yes( $severity->high,  $threshold->low );
    $problem->no( $fe->not( $problem->yes )  );

    # Fuzzy results are represented by the membership degrees of sets 
    print 'Problem yes: ', $problem->yes,  "\n";
    # [
    #  [         0 0.33333333 0.33333333 0.33333333]
    #  [         0        0.5          1          1]
    # ]

    # Defuzzify the output variables
    # Caveat: This includes some non-threadable operations up to now
    my $problem_ratings = $problem->defuzzify();
    print 'Problems rated: ', $problem_ratings;
    # [
    #  [         0 0.60952381 0.60952381 0.60952381]
    #  [         0       0.75          1          1]
    # ]

EXPORT ^

Nothing is exported or exportable.

DESCRIPTION ^

This module is yet another implementation of a fuzzy inference system. The aim was to be able to code rules (no string parsing), but avoid operator overloading, and make it possible to split calculation into multiple steps. All intermediate results (memberships of sets of variables) should be available.

Beginning with v0.2.0 it is PDL aware, meaning that it can handle piddles (PDL objects) when running the fuzzy operations. More information on PDL can be found at http://pdl.perl.org/.

Credits to Ala Qumsieh and his AI::FuzzyInference, that showed me that fuzzy is no magic. I learned a lot by analyzing his code, and he provides good information and links to learn more about Fuzzy Logics.

Fuzzy stuff

The AI::FuzzyEngine object defines and provides the elementary operations for fuzzy sets. All membership degrees of sets are values from 0 to 1. Up to now there is no choice with regard to how to operate on sets:

$fe->or( ... ) (Disjunction)

is Maximum of membership degrees

$fe->and( ... ) (Conjunction)

is Minimum of membership degrees

$fe->not( $var->$set ) (Negation)

is 1-degree of membership degree

Aggregation of rules (Disjunction)

is Maximum

True $fe->true() and false $fe->false()

are provided for convenience.

Defuzzification is based on

Implication

Clip membership function of a set according to membership degree, before the implicated memberships of all sets of a variable are taken for defuzzification:

Defuzzification

Centroid of aggregated (and clipped) membership functions

Public functions

Creation of an AI::FuzzyEngine object by

    my $fe = AI::FuzzyEngine->new();

This function has no parameters. It provides the fuzzy methods or, and and not, as listed above. If needed, I will introduce alternative fuzzy operations, they will be configured as arguments to new.

Once built, the engine can create fuzzy variables by new_variable:

    my $var = $fe->new_variable( $from => $to,
                        $name_of_set1 => [$x11, $y11, $x12, $y12, ... ],
                        $name_of_set2 => [$x21, $y21, $x22, $y22, ... ],
                        ...
                   );

Result is an AI::FuzzyEngine::Variable. The name_of_set strings are taken to assign corresponding methods for the respective fuzzy variables. They must be valid function identifiers. Same name_of_set can used for different variables without conflict. Take care: There is no check for conflicts with predefined class methods.

Fuzzy variables provide a method to fuzzify input values:

    $var->fuzzify( $val );

according to the defined sets and their membership functions.

The memberships of the sets of $var are accessible by the respective functions:

    my $membership_degree = $var->$name_of_set();

Membership degrees can be assigned directly (within rules for example):

    $var->$name_of_set( $membership_degree );

If multiple membership_degrees are given, they are "anded":

    $var->$name_of_set( $degree1, $degree2, ... ); # "and"

By this, simple rules can be coded directly:

    my $var_3->zzz( $var_1->xxx, $var_2->yyy, ... ); # "and"

this implements the fuzzy implication

    if $var_1->xxx and $var_2->yyy and ... then $var_3->zzz

The membership degrees of a variable's sets can be reset to undef:

    $var->reset(); # resets a variable
    $fe->reset();  # resets all variables

The fuzzy engine $fe has all variables registered that have been created by its new_variable method.

A variable can be defuzzified:

    my $out_value = $var->defuzzify();

Membership functions can be replaced via a set's variable:

    $var->change_set( $name_of_set => [$x11n, $y11n, $x12n, $y12n, ... ] );

The variable will be reset when replacing a membership function of any of its sets. Interdependencies with other variables are not checked (it might happen that the results of any rules are no longer valid, so it needs some recalculations).

Sometimes internal variables are used that need neither fuzzification nor defuzzification. They can be created by a simplified call to new_variable:

    my $var_int = $fe->new_variable( $name_of_set1 => [],
                                     $name_of_set2 => [],
                                     ...
                       );

Hence, they can not use the methods fuzzify or defuzzify.

Fuzzy operations are simple operations on floating values between 0 and 1:

    my $conjunction = $fe->and( $var1->xxx, $var2->yyy, ... );
    my $disjunction = $fe->or(  $var1->xxx, $var2->yyy, ... );
    my $negated     = $fe->not( $var1->zzz );

There is no magic.

A sequence of rules for the same set can be implemented as follows:

    $var_3->zzz( $var_1->xxx, $var_2->yyy, ... );
    $var_3->zzz( $var_4->aaa, $var_5->bbb, ... );

The subsequent application of $var_3->zzz(...) corresponds to "or" operations (aggregation of rules).

Only a reset can reset $var_3.

PDL awareness

Membership degrees of sets might be either scalars or piddles now.

    $var_a->memb_fun_a(        5  ); # degree of memb_fun_a is a scalar
    $var_a->memb_fun_b( pdl(7, 8) ); # degree of memb_fun_b is a piddle

Empty piddles are not allowed, behaviour with bad values is not tested.

Fuzzification (hence calculating degrees) accepts piddles:

    $var_b->fuzzify( pdl([1, 2], [3, 4]) );

Defuzzification returns a piddle if any of the membership degrees of the function's sets is a piddle:

    my $val = $var_a->defuzzify(); # $var_a returns a 1dim piddle with two elements

So do the fuzzy operations as provided by the fuzzy engine $fe itself.

Any operation on more then one piddle expands those to common dimensions, if possible, or throws a PDL error otherwise.

The way expansion is done is best explained by code (see AI::FuzzyEngine->_cat_array_of_piddles(@pdls)). Assuming all piddles are in @pdls, calculation goes as follows:

    # Get the common dimensions
    my $zeros = PDL->pdl(0);
    # Note: $zeros += $_->zeros() for @pdls does not work here
    $zeros = $zeros + $_->zeros() for @pdls;

    # Expand all piddles
    @pdls = map {$_ + $zeros} @pdls;

Defuzzification uses some heavy non-threading code, so there might be a performance penalty for big piddles.

Todos

Add optional alternative implementations of fuzzy operations
More checks on input arguments and allowed method calls
PDL awareness: Use threading in $variable->defuzzify
Divide tests into API tests and test of internal functions

CAVEATS / BUGS ^

This is my first module. I'm happy about feedback that helps me to learn and improve my contributions to the Perl ecosystem.

Please report any bugs or feature requests to bug-ai-fuzzyengine at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=AI-FuzzyEngine. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc AI::FuzzyEngine

AUTHOR ^

Juergen Mueck, jmueck@cpan.org

COPYRIGHT ^

Copyright (c) Juergen Mueck 2013. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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