### Learning a MR

```Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Learning the Parameters of a Multiple Criteria
Sorting Method Based on a Majority Rule
Agnes Leroy1 , Vincent Mousseau2 , Marc Pirlot1
1 MATHRO,
Faculté Polytechnique, U-Mons, Belgium
[email protected]
2 LGI,
Ecole Centrale Paris, France
[email protected]
ADT Conference, Rutgers, Oct. 26-28, 2011
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Contents
1
Introduction
2
MR-Sort: a sorting method based on a majority rule
3
Learning a MR-Sort model
4
Empirical design
Experiment 1:
Experiment 2:
Experiment 3:
5
Conclusion
and results
model retrieval
tolerance for error
idiosyncratic behavior
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Sorting problem statement
Multicriteria sorting problem
Alternatives evaluated on multiple criteria...
... to be assigned to (predefined) ordered categories
Absolute rather than comparative evaluation
Typical examples
Granting bank credits,
Evaluating research projects,
Attribute merits to students,
Evaluating objects on an ordinal scale.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
MR-Sort : Simplified Electre Tri method
1
Define categories using limit profiles B = {b1 , b2 , . . . , bp },
C1
C2
Cp−1
Cp+1
Cp
g1
g2
g3
gm−1
gm
b0
b1
bp−1
bp
bp+1
2
Compare a ∈ A to b1 , ..., bp using a majority relation ,
3
Assign a to the highest category Ch for which a bh .
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Learning an MR-Sort model sorting from examples
Inference procedure
Input = assignment examples
alternatives that should be assigned to a given category
Output = values for the parameters of the sorting model,
Inference procedure = algorithm which learns the parameters
of the sorting model from assignment examples.
Our aim
Empirical investigation of the behavior of the inference procedure
for the MR-Sort model
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experimental questions
Q1 Model retrieval: when examples are assigned by a simulated
MR-Sort, does the learning method elicit a model “close” to
the original one ? What is the size of a learning set to obtain
a “good approximation”?
Q2 Tolerance for error: when the learning set contains errors (5
to 15%), to what extent do these errors perturb the elicitation
of the assignment model?
Q3 Idiosyncrasy: we assign examples using an additive value
function, and learn an MR-Sort model. Can we detect a
change in the model with the learning procedure? Can the
models be discriminated on an empirical basis, i.e., on the sole
evidence of assignment examples?
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Contents
1
Introduction
2
MR-Sort: a sorting method based on a majority rule
3
Learning a MR-Sort model
4
Empirical design
Experiment 1:
Experiment 2:
Experiment 3:
5
Conclusion
and results
model retrieval
tolerance for error
idiosyncratic behavior
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
MR-Sort [Bouyssou, Marchant 2007]
Notation
n criteria, N = {1, . . . , n},
Xi values on criterion i ,
Q
X = ni=1 Xi ,
2 categories : ordered bipartition (X 1 ,X 2 ) of X ,
for each criterion i , there is a partition (Xi1 , Xi2 ) of Xi ,
F a family of “sufficient” coalitions of criteria (subsets of N),
x = (x1 , . . . , xi , . . . , xn ) ∈ X 2
Leroy, Mousseau, Pirlot
iff
{i ∈ N|xi ∈ Xi2 } ∈ F.
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
MR-Sort procedure
Further hypothesis
Xi ⊂ R, and the partitions (Xi1 , Xi2 ) of Xi (i ∈ N) are:
compatible with the order on R,
represented by bi the smallest element in Xi2 .
weights wiP
≥ 0, i ∈ N andPλ are defined s.t. for F ⊆ N,
F ∈ F iff i ∈N wi ≥ λ ( i ∈N wi = 1)
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Contents
1
Introduction
2
MR-Sort: a sorting method based on a majority rule
3
Learning a MR-Sort model
4
Empirical design
Experiment 1:
Experiment 2:
Experiment 3:
5
Conclusion
and results
model retrieval
tolerance for error
idiosyncratic behavior
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Learning a MR-Sort model
A∗ = {a1 , . . . , aj , . . . , ana },
Learning set: bipartitions (A∗1 , A∗2 )
Two categories separated by a frontier b = (b1 , ..., bn ),
Define δij ∈ {0, 1}, i ∈ N, aj ∈ A∗ s. t. δij = 1 ⇔ gi (aj ) ≥ bi
and δij = 0 ⇔ gi (aj ) < bi ,
M(δij − 1) ≤ gi (aj ) − bi < M · δij
δij ∈ {0, 1}
Define cij such that cij = 0 ⇔ δij = 0 and cij = wi ⇔ δij = 1,
wi weight of criterion i .
⇒ δij − 1 + wi ≤ cij ≤ δij and 0 ≤ cij ≤ wi ,
P
i ∈N cij
=
P
i :gi (aj )≥bi
wi ,
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Learning a MR-Sort model
a → C2 ⇔
a → C1 ⇔
P
Pi ∈N
cij ≥ λ,
i ∈N cij
+ ε ≤ λ,
introduce a slack variable s,
P
a → C2 ⇔ j∈N cij = λ + α,
P
a → C1 ⇔ j∈N cij + ε + α = λ,
α ≥ 0 ⇔ conform to assignment examples
Max α s.t. previous constraints
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Learning a MR-Sort model
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α
P
Pi ∈N cij + xj + ε = λ
i ∈N cij = λ + yj
α ≤ xj , α ≤ yj
cij ≤ wi
cij ≤ δij
cij ≥ δij − 1 + wi
Mδij + ε ≥ gi (aj ) − bi
M(δ
P ij − 1) ≤ gi (aj ) − bi
i ∈N wi = 1, λ ∈ [0.5, 1]
wi ∈ [0, 1]
cij ∈ [0, 1], δij ∈ {0, 1}
xj , yj ∈ R
α∈R
Leroy, Mousseau, Pirlot
∀aj
∀aj
∀aj
∀aj
∀aj
∀aj
∀aj
∀aj
∈ A∗1
∈ A∗2
∈ A∗
∈ A∗ , ∀i ∈ N
∈ A∗ , ∀i ∈ N
∈ A∗ , ∀i ∈ N
∈ A∗ , ∀i ∈ N
∈ A∗ , ∀i ∈ N
∀i ∈ N
∀aj ∈ A∗ , ∀i ∈ N
∀aj ∈ A∗
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Infeasible learning sets
γj = 1 if alternative aj is correctly assigned, γj = 0 otherwise,
P
∗1
Pi ∈N cij < λ + M(1 − γj ), ∀aj ∈ A∗2
i ∈N cij ≥ λ − M(1 − γj ), ∀aj ∈ A
P
Objective function: Max aj ∈A∗ γj
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Contents
1
Introduction
2
MR-Sort: a sorting method based on a majority rule
3
Learning a MR-Sort model
4
Empirical design
Experiment 1:
Experiment 2:
Experiment 3:
5
Conclusion
and results
model retrieval
tolerance for error
idiosyncratic behavior
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Empirical design
We run 10 instances of each of the problems obtained by varying
the following parameters:
Two, three categories,
Three, four, five criteria,
Learning sets containing 10 to 100 alternatives.
MIPs solved with CPLEX
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Experiment 1: model retrieval, “learnability ”
Empirical questions
Does the learning method elicit a model “close” to the
original one?
What is the size of a learning set to obtain a “good
approximation”?
Varying the size of the model and the number of assignment
examples, we evaluate
the % of assignment errors on a set of 10000 alternatives,
the computing time.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
assignment errors ց when learning set size ր,
For a given learning set size, % error ր with the number of param.
To keep error<10%, we need 40 (resp. 70) examples for 2 (resp. 3)
categories, 5 criteria,
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
CPU time<10s for 2 and 3 categ., up to 4 crit., 100 examples,
In the case 3 categories, 5 criteria = 25s for 100 examples
⇒ CPU time can soon become unacceptable for larger size.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Experiment 2: Tolerance for errors
Empirical question
to what extent do assignment errors perturb the elicitation of
the assignment model?
are the corresponding elicitation programs harder to solve?
varying the size of the learning sets, with 2 categ. and 3 crit., we
evaluate
the max % of correct re-assignment of examples,
the % of assignment errors on a set of 10000 alternatives,
the computing time.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
the max % of correct re-assignment of examples ց from a high
value to reach asymptotically a minimum, as the learning set size ր
the asymptotic minimum corresponds to the % of correct
assignments.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
the % of assignment errors on a set of 10000 alternatives ց, as the
learning set size ր,
a limited number of errors does not strongly impact “learnability”,
for learning sets > 40 examples, errors slightly deteriorates the
ability of the model to restore the assignment of random
alternatives.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Computing time in Experiment 2
CPU time increases with the size of the learning set, for all
proportion of errors,
for large learning sets (>50 examples) the % of errors in the
learning set significantly ր CPU time.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
Experiment 3: idiosyncratic behavior
Empirical question
we define the learning set using an additive value function,
and learn an MR-Sort model.
Can we detect a change in the model with the learning
procedure?
Can the models be discriminated on an empirical basis, i.e.,
on the sole evidence of assignment examples?
varying the size of the learning sets, with 2 or 3 categ., we evaluate
the max % of correct re-assignment of examples,
the computing time.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
2 categories
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Experiment 1: model retrieval
Experiment 2: tolerance for error
Experiment 3: idiosyncratic behavior
3 categories
MR-Sort models are flexible enough to accommodate more than
95% (resp. 90%) of additive-Sort examples with 2 (resp. 3) categ,
it is uneasy to detect, on the sole basis of assignment examples,
which sorting model has been used to generate the learning set.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Contents
1
Introduction
2
MR-Sort: a sorting method based on a majority rule
3
Learning a MR-Sort model
4
Empirical design
Experiment 1:
Experiment 2:
Experiment 3:
5
Conclusion
and results
model retrieval
tolerance for error
idiosyncratic behavior
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
Introduction
MR-Sort: a sorting method based on a majority rule
Learning a MR-Sort model
Empirical design and results
Conclusion
Conclusion and further research
eliciting an MR-Sort model is highly demanding in terms of
information,
Parsimony in the choice of a model: the scarcity of available
information should lead the analyst to avoid models involving
many parameters,
MR-Sort expressive power is sufficient when the learning set
contains a few dozens of examples,
Selecting informative assignment examples: Developing a
methodology for efficiently eliciting sorting or ranking models
by learning,
Experimental analysis of learning methods in MCDA is a
subject that has not received enough attention sofar.
Leroy, Mousseau, Pirlot
Learning a majority rule sorting model
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