Type-1 OWA operators

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Type-1 OWA operators [1] [2] are a set of aggregation operators that generalise the Yager's OWA (ordered weighted averaging) operators) [3] in the interest of aggregating fuzzy sets rather than crisp values in soft decision making and data mining.

Contents

These operators provide a mathematical technique for directly aggregating uncertain information with uncertain weights via OWA mechanism in soft decision making and data mining, where these uncertain objects are modelled by fuzzy sets.

The two definitions for type-1 OWA operators are based on Zadeh's Extension Principle and -cuts of fuzzy sets. The two definitions lead to equivalent results.

Definitions

Definition 1

Let be the set of fuzzy sets with domain of discourse , a type-1 OWA operator is defined as follows: [2]

Given n linguistic weights in the form of fuzzy sets defined on the domain of discourse , a type-1 OWA operator is a mapping, ,

such that

where , and is a permutation function such that , i.e., is the th highest element in the set .

Definition 2

Using the alpha-cuts of fuzzy sets: [2]

Given the n linguistic weights in the form of fuzzy sets defined on the domain of discourse , then for each , an -level type-1 OWA operator with -level sets to aggregate the -cuts of fuzzy sets is:

where , and is a permutation function such that , i.e., is the th largest element in the set .

Representation theorem of Type-1 OWA operators

Given the n linguistic weights in the form of fuzzy sets defined on the domain of discourse , and the fuzzy sets , then we have that [2]

where is the aggregation result obtained by Definition 1, and is the result obtained by in Definition 2.

Programming problems for Type-1 OWA operators

According to the Representation Theorem of Type-1 OWA Operators, a general type-1 OWA operator can be decomposed into a series of -level type-1 OWA operators. In practice, this series of -level type-1 OWA operators is used to construct the resulting aggregation fuzzy set. So we only need to compute the left end-points and right end-points of the intervals . Then, the resulting aggregation fuzzy set is constructed with the membership function as follows:

For the left end-points, we need to solve the following programming problem:

while for the right end-points, we need to solve the following programming problem:

A fast method has been presented to solve two programming problem so that the type-1 OWA aggregation operation can be performed efficiently, for details, please see the paper. [2]

Alpha-level approach to Type-1 OWA operation

Three-step process: [2]

  • Step 2.1To calculate
  1. Let ;
  2. If , stop, is the solution; otherwise go to Step 2.1-3.
  3. , go to Step 2.1-2.
  • Step 2.2 To calculate
  1. Let ;
  2. If , stop, is the solution; otherwise go to Step 2.2-3.
  3. , go to step Step 2.2-2.

Some Examples

T1OWA 4Weights.jpg
T1OWA 4FuzzySetsAggregatedBy4Weights.jpg

Special cases

Generalizations

Type-2 OWA operators [7] have been suggested to aggregate the type-2 fuzzy sets for soft decision making.

Applications

Type-1 OWA operators have been applied to different domains for soft decision making.

Related Research Articles

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